grrrnthumb

Homemade potting soil / soil science questions

grrrnthumb
12 years ago

Well I would sure like your critique of my homemade soil mix. Here's the recipe I've developed over the years:

5 gal TBK coarse blonde sphagnum peat moss

5 gal ground coconut coir

5 gal perlite

5 gal horticultural pumice

5 gal Cedar Grove bagged compost (least wood, most composted; brand is important)

3 cups alfalfa meal

1.5 cups kelp meal

1 cup bone meal

1 cup ground dolomite

1 cup Osmocoat slow release 14-14-14

.5 cup Scott's Starter Fertilizer 20-27-5

I mix the 5 major ingredients in an extra large wheelbarrow. Mix the minor ingredients in a small bucket and sprinkle them finely into the wheelbarrow, stopping to mix with the shovel several times.

This mix gives the water retention (peat, coir), the drainage (perlite, pumice), and the organics (compost) in a ratio of about 1:1:1/2, which works great for a wide variety of tropicals & houseplants. I will sometimes add extra pumice for succulents and the like.

What I'm most concerned about is if you think I can improve the minor ingredients. Maybe too much or not enough lime, too much fertilizer, etc.

Also on PH testing, I know that soils age and take some time to ripen the ingredients together. Is there a preferred method of testing an artificial soil for PH?

How about comprehensive testing, anyone know how much that may cost and where I can have it done? Thanks!

- Tom

Comments (59)

  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    "If a simple mix was used to grow a plant before the final consumer bought it, why would it need a complicated one later?"
    We need to look at what makes commercial production growers different from regular people:
    1) They have a short turn-around cycle and the mix doesn't need a long life. Bark mixes change even over 1 year, but drastically over 2-3 years in water retention, drainage, ph, and tannin (poison) release. They're not consistent long-term.
    2) Machine dosed nutrients capable of fully supporting growth without much help from the mix. Your friend growing thousands of tropicals in bark and sand is really growing hydroponically. It works great if you have the equipment, but most of us don't have it. We need slowly available nutrients in the mix to provide even, consistent, wide spectrum nutrient availability.
    3) Automatic watering, or employees that can maintain a perfect schedule plus water twice as often as the rest of us. Thus the air to water holding ratio of the soil is never really challenged. They can just use anything coarse because their watering is perfect. A high quality mix has enough air exchange to grow agave and aloe, but enough water holding capacity for petunias to thrive even with an irregular watering schedule.
    --
    Bboy I know you have a predisposition towards reducing ammendments. If you are talking overall volume of combined nutrients in the mix, then I'm with you. In fact that's the reason for this thread, because I think I have it too high. But if you are just against complexity (many ingredients in proper proportions), then I have to strongly disagree. These are not ammendments, but ingredients in an artificial soil that is still far less diverse and complex than natural soil. There are soooo many ways that a complex mix provides saftey from overdosing or from one nutrient making another unavailable, and many ways that ingredients work together. For instance:
    - Perlite is very light, and it's really the best at adding air to the mix while also storing some moisture and not breaking down too quickly, but it has the really annoying habit of floating to the top in mixes where it predominates. You can eliminate this by cutting it 50% with pumice and still get nearly the air capacity plus you're adding extra mineral diversity like natural soils.
    - Peat & bark mixes have too high ph naturally. Some form of lime is usually used to bring it up, but single-source lime often is either used up too fast or becomes available too slow. Multiple sources provides a more consistent availability.
    - Sphagnum peat is the best at holding lots of water while still allowing some air, but it's ph is too low and it's becoming less environmentally freindly. Cutting it 50% with coir reduces both those problems and still gives nearly the performance while providing extra chemical diversity.
    Sorry for the length, I'll stop babbling now. :^)
    - Tom

  • gardengal48 (PNW Z8/9)
    12 years ago
    last modified: 5 years ago

    I'm not sure your mix is overly complicated. The better commercially prepared potting mixes also tend to have a wide range of ingredients, many of which match pretty closely to your recipe. In fact my preferred potting mix, Gardner&Bloome Blue Ribbon Potting Soil, is darn close to your recipe. And there are quite different requirements for a long term container planting mix than there is for a growers mix, which tends to be intended for the short term. The eventual compaction that will occur with the breakdown of the components of these mixes is far less of a concern than it is for a mix intended for a long term container situation. Personally I'd be hesitant about adding any garden soil or much compost, as these both tend to be too heavy, without adequate pore space or too inclined towards continued decomposition and compaction to add much value to a long term mix. Bark fines are most often recommended or included, for the simple reason they do NOT breakdown as rapidly and add needed texture. Since container plantings are also regularly fertilized, any nitrogen tie-up they may produce is not an issue.

    I use the same mix for all planting situations - both indoor and outdoor plants as well as cacti and succulents. I do alter the mix a bit for the succulents or trough garden plants by adding additional pumice and coarse sand. I do very few seasonal container plantings for myself - most of these are permanent plantings of trees, shrubs and perennials and are intended for at least 2-3 growing seasons before requiring repotting or refreshing.

    You might want to review some of the postings on the Container Gardening forum for additional input on your container mix. There are some serious container gardening posters there and several of them can offer detailed explanations on why they opt for the mixes they do. You may find it very helpful.

    Here is a link that might be useful: Gardner&Bloome Blue Ribbon Potting Soil

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  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    Thanks for the info Gardengal. I do the same as you by adding pumice to fine-tune the mix for xerics.
    I do have to disagree with you on one small point though. Bark fines are not added mainly for texture and long life. They are not nearly as good at those two things as the other ingredients we've mentioned. The real reason they are added is cost. They are the *cheapest* filler. They do add drainage and a tiny bit of water retention. You can look at the spectrum of price across all artificial soils and see that you do get what you pay for. The best mixes have the least bark, while the cheapest mass-produced muck mixes have the most bark and the largest sticks.
    Bark does have a long life in one sense, drainage, but drainage goes hand-in-hand with moisture retention in any ingredient, and that's where bark has a problem. It has very little moisture retention at all to begin with, and then as it ages it changes quickly until it has too much. It's not a stable ingredient.
    I've grown epiphytic orchids in bark for 20 years (I have 3 kinds of bark mixes I make for them), and it just changes too much to be useable for more than a year. Many plants really slow down the second year in bark mixes.
    I appreciate that link, it looks interesting. I'll look it up. :^)
    - Tom

  • mdvaden_of_oregon
    12 years ago
    last modified: 5 years ago

    Probably depends on how "fine" that fine is with the bark.

    I've seen gardeners, and even golf course superintendents for greens, use it for a long-term reservoir of potential organic matter, since it decomposes over a long period of time, releasing substances over that long period of time.

    So the soil blends can be handled in more than one way:

    a. Very fine and decomposed.
    b. Less fine, partially decomposed.

    M. D. Vaden of Oregon

  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    You seem to be saying that "decomposed" is finished decomposing. Are you saying that the high carbon content in bark is going to stop sucking excessive nitrogen when it reaches a certain stage?
    I thought it actually sped up as it ages becuase bark decomposes faster as it gets finer (more surface area as it breaks apart).

  • gardengal48 (PNW Z8/9)
    12 years ago
    last modified: 5 years ago

    Generally the concern of nitrogen unavailability in a potting medium that incorporates a wood product is negated by the need to provide supplemental fertilization anyway. Bark fines, regardless of the degree of decomposition, do not tie up nearly as much nitrogen as does something like sawdust, with a much higher surface area per volume than even the finest grade of bark fines. Nitrogen unavailability is of far greater concern when applying this type of product to garden soils, primarily because of the existing organic matter and the plethora of soil organisms speeding up the breakdown. Because potting media for container culture is comprised primarily of inert or extremely slow to decompose organic materials with a noticeable lack of similar populations of soil microorganisms, nutrient unavailability or deficiencies will always be present unless supplemented. Leaching through frequent watering will account for a similar need. If the need for supplemental fertilizing is a given in container growing - and I think we can all agree on that - then the potential, however great or meager it may be, for nitrogen unavailability due to incorporating a wood product like bark fines is a moot issue. Just supply enough nitrogen to compensate.

    If bark was such a problem, there'd be a lot of orchid growers in trouble :-)

  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    " Generally the concern of nitrogen unavailability in a potting medium that incorporates a wood product is negated by the need to provide supplemental fertilization anyway."
    - I'd have to disagree with that one. Excessive nitrogen use and also the need for excessive supplemental fertilization is a defect, not an inevitability, of potting soils. That's one of the reasons that I like my mix.
    - " Because potting media for container culture is comprised primarily of inert or extremely slow to decompose organic materials with a noticeable lack of similar populations of soil microorganisms, nutrient unavailability or deficiencies will always be present unless supplemented."
    -
    I can sure agree that mostly inert (dead) mixes are mostly devoid of soil microorganisms. Not all mixes are that way though; mine isn't. Those microorganisms are essential for a smooth even and full uptake of nutrients in the soil. You can have lots of nutrients in the soil that our plants just can't get to fast enough without those microorganisms.
    If you don't have a professional dosing system tied into automatic watering, Then your elements are coming at the plants in a herky-jerky, too-much-then-too-little fashion. Plants are much more prone to disease and deficencies. A mix containing organic nutrients with live microorganisms will dose those nutrients naturally, evenly, and without the up-and-down spikes of manually fertilizing dead mixes.
    I won't say I want 100% fertilization just through the potting soil (becuase many plants I grow require less than others), but I will say that the soil should provide a nice basic set of nutrients for average simple plant growth as a starting point.
    Orchid fertilizers are a good example. They most commonly are high in nitrogen, such as 30-10-10, to get an eventual balanced dose after the bark has had it's fill. When you pump up the chemicals so high to make up for the bark, then you're mass killing the microorganisms and you're going back to the irregular ups & downs of elemental fertilization. Hence you'll very often see orchid quotes like this one: "Smaller doses on a regular basis produce more consistent growth and healthier plants." It's tough to grow them non-organically, but I do the bark mixes for orchids too because I don't know any other way that will work. Not true with regular potting soil. :^)
    - Tom

  • mdvaden_of_oregon
    12 years ago
    last modified: 5 years ago

    I think what gardengal shared would be more comparable to how all soils have not the same water needs, and different amounts of water would be required by different soils.

    It's outside the realm of "excessive" and in the realm of what does it need.

    Likewise with fertilizer. "Extra" may not equal "excessive" if a gardener is adding just enough more for the microorganisms, but not enough for waste.

  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    MDvaden when I say that bark mixes require excessive nitrogen, I don't really mean in the sense that it's wasted down the drain. Even if you were to add only exactly what is used by the bark and the plant, it is still excessive because you need so much nitrogen that it's no longer practical to get most of it from organic components in the mix. It's also excessive because even if you get the exact right amount, you still have to kill a large percentage of your microorganisms with all those chemical fertilizers necessary to get proper nitrogen levels, which then requires even more chemical fertilizers.

  • gardengal48 (PNW Z8/9)
    12 years ago
    last modified: 5 years ago

    grrrnthumb, I think you have different understanding of container culture than I do and perhaps that's where we differ. Many folks think that just replicating an inground growing condition will work for a container planting as well. And to be honest, it will - for a relatively short period of time. But container culture is an extremely artificial growing condition and for any long term success, one has to make concessions for the requirements this situation demands.

    Containers need to be watered frequently; in summer, daily or more often. Every time they are watered, nutrients are leached out from the potting soil. As a container is a closed environment with a limited supply of nutrients at the outset, the constant leaching of what may be available requires that the supply be refreshed. And often.

    Because of the need for a container potting medium to be freely draining demands a high proportion of inert ingredients, organic matter tends to be limited and what there is, slow to decompose. This presents some habitat issues for typical soil microorganisms. They are simply not present in high enough numbers to be of significant value nor is the container environment particularly conducive to their proliferation. So that limits what they can contribute to the natural conversion of what OM might be present or any granular (insoluble) organic fertilizers into a soluble nutrient form the plant roots can access. Again, to keep long term planted containers happy and thriving, soluble or immediately available nutrients are provided in the form of fertilizer.

    you need so much nitrogen that it's no longer practical to get most of it from organic components in the mix. No and yes. No, it's not that much nitrogen - you are overcompensating if you think the nitrogen depletion/unavailability in a typical container that uses a wood product in the mix is going to be that severe. It's just not. And yes, it's NOT practical to expect all the nitrogen requirements will be obtained from organic components in the mix, nor the rest of the other required plant nutrients. If the mix were entirely OM, you'd still not generate sufficient nitrogen or other nutrients to satisfy the plants' requirements long term. You DO need to supplement. And if you are serious about maintaining an completely organic container growing situation, these nutrients can be supplemented with a liquid (soluble) organic fertilizer formulation, like fish emulsion, liquid kelp or several others, that does not require the activities of high populations of microorganisms to digest and make available.

  • mdvaden_of_oregon
    12 years ago
    last modified: 5 years ago

    Microorganisms live on their own in the wild. And not by using nothing.

    They use something, even if minor and inconsequential. And whatever that small amount is, it's essential to them.

    Whether composted material or bark is in the pot, or in the forest, microorganisms can be present and will require some elements in excess of the exact amount required by any plants in the area.

  • ian_wa
    12 years ago
    last modified: 5 years ago

    I think on a more philosophical level.... container gardening is fundamentally unnatural vs. growing plants in the ground in real soil. I think we would agree that soil from the ground is generally unsuitable for growing healthy plants in containers. So as long as we're doing something un-natural to begin with, we each need to just figure out what works best for our individual purposes.

    The wholesale grower whose plants deteriorate quickly at the retailer because they require too much maintenance relative to plants from other wholesalers will either figure out how to change or face extinction as a business. I've noticed more than one retailer no longer purchasing from a certain mega-wholesale nursery whose name begins with "H" for this reason.

  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    Ian I can sure agree with that. I don't mean to say that bark is wrong for all situations, in fact I do use it myself for orchid mixes. I took a look at your web site (great site!) and it looks like you focus more towards Australian & South African type plants, especially eucalyptus. That seems to work well with bark mixes because of their native soils commonly being higher in carbon & lower in organics than other tropicals on average.
    -
    Mdvaden I do apologize for saying so, but that is not correct. The organisms that break down organic matter (both the compost & the bark you mentioned), use mainly carbon and nitrogen in a ratio of about 20:1. In organic matter that has that ratio of 20 carbon to 1 nitrogen, there is a balance where decomposition does not use more nitrogen than is produced by their waste. At about a 30:1 ratio the bacteria begin "stealing" nitrogen, or using up more than they produce; getting it from sources such as applied fertilizers before it is available to the plants. Fir bark is the most common bark ammendment in this area. It's carbon to nitrogen ratio is 500:1! Compost is lower than the 30:1 tipping point, and so it does not rob nitrogen.
    -
    Gardengal yes I think we differ in how we grow in containers. It looks like you water much more than I do, so I imagine you're using a super free-draining bark type mix with some of the mechanical dosing & watering advantages that make this method work great commercially.
    Normal people are very poor at regular fertilization, and the plants suffer from that irregularity in dead mixes.
    Let me clarify that I didn't say you should get all nutrients from the mix, just a basic minimum that can keep the plant going modestly and keep the mycorrhiza in the soil alive. It is fairly bold of you to say it is not possible. I have done it and I have proved it. I am showing you a mix that will do just that, for 3 years or more. Here is a picture of an epiphylum that's been in the same mix, unchanged, for 6 years now.




    The mix is the same as above but with less volume of minor ingredients added. I quit fertilizing it after year 2 as an experiment. I get 2 bloom flushes a year from it reliably, but I think I'll repot this year because the soil is all gone; it's pure roots. I have many more tropicals in the same kind of mix for 3 years or more that are also doing well. I fertilize very little except the brugmansia, which are real pigs.
    Leaching is more a concern for your mix because you are using only elemental nutrients. The 3 kinds of meal and especially the compost provide long term dosing of nutrients from a coarse structure that isn't all washed out like liquid fertilizers.
    If you get a good portion of your nutrients from slow release organics, and don't kill your mycorrhiza with lots of bark & lots of elemental fertilizers, then the mix will feed your plants long term in a controlled, dosed way that provides a big margin of error for our imperfections. :^)
    - Tom

  • nwnatural
    12 years ago
    last modified: 5 years ago

    That is a beautiful Epiphyllum, but as you stated in your post, they hardly need any soil to grow in. In their native habitat, Epiphyllums grow in tree crotches getting most of their nutrients from the tropical air.

    I think your soil can grow more than cacti, it sounds like a pretty good mix.

    Here is a link that might be useful: Epiphyllum

  • greenelephant
    12 years ago
    last modified: 5 years ago

    Dear Tom,

    Excellent topic. Your mix is exquisite, if not a bit complicated.

    A friend of mine uses an electric cement mixer to make his batches. He uses 1 part ground peat, 1 part well-rotted compost, 1 part Tagro (this is a sawdust/lime/boisolids mix from Tacoma's sewage treatment) 1 part sawdust, and a cup of lime.

    His mix is super cheap, featherlight, and his plants grow like a house afire.

    ---------
    Myself. I use 100%, 2-year-old composted leaves. Some plants fare better than others in it. (I would never use it for houseplants.) Trees grow very well in it.

    I fertilize depending on the need.

    Again, thanks for the topic.

    Jim

  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    Thank you nwnatural. I chose the epi becuase I thought it is a good test for soils. They require air exchange/porosity almost like a desert cacti, yet they need water retention almost like a typical tropical. In most soil mixes they require very good watering regularity to thrive.
    Also, it's true they get some nutrients from the air (water, carbon, and maybe some nitrogen), but these have massive, fleshy blooms in big flushes twice a year. They still must get plenty of phosphorus and most other nutrients from their roots.
    Here are a couple more:



    The first is an Alocasia that has been in that pot for just over 3 years now, and hasn't been fertilized for over a year. These are good tests for soils because they tend to throw smaller leaves as the mix wears out. The newest leaf is 23" across.
    Second is an Amorphophallus titanum. They are very finicky about their type of soil. These need to be replanted every leaf cycle, but they come from Sumatra which is without seasons. So the leaf cycle can be up to a couple years, and they are very, very sensitive to a soil mix "souring" as it ages. I use extra pumice with that one. It's about 4' high now and his been in that pot for about 2 years, it's just now starting to shed this leaf.
    -
    Jim that Tagro has intrigued me, but I'm too chicken to try it because of what it is, lol.
    - Tom

  • sissysimone
    12 years ago
    last modified: 5 years ago

    Sorry, but where do you get.

    coarse blonde sphagnum peat moss and
    Cedar Grove bagged compost ?
    Is there other stuff comparable to these products since I live in New Hampshire and highly doubt that I can fine these ingrediants locally. Thankyou!! :-)

  • grrrnthumb
    Original Author
    12 years ago
    last modified: 5 years ago

    Hi Sissy,
    For the moss, do a google search for tbk moss. It's available all over, including online. It holds more air & packs less than regular peat.
    For the compost, you're right that brand is strictly local. I'll describe it so you may find something similar. It's pure compost from shredded yard waste collected by local municipalities. It is screened to 3/8 inch and aged 18 months in huuuge piles that generate incredible heat, effectively sterilizing the weeds & nasties. It is friable, loose, airy, and yet high in moisture retention. It is very low in woody matter, which usually makes up a huge portion of most "composts".
    BTW, if you decide to do something similar, use less fertilizers than I did. I quit being lazy and did some math on my original question and I think I am too high in nutrients for many plants. I'm using up that batch on the brugmansias, which love tons of fertilzer.

  • brucestay
    9 years ago
    last modified: 5 years ago

    I came across this thread and notice there are many members in the greater Seattle area using pumice in their mix. Where do you get it? I have looked and only found small bags which are way too expensive.

  • morz8
    9 years ago
    last modified: 5 years ago

    Bruce, I'm not sure we'd have matching definitions of big or expensive :) but for my needs, I've been buying Black Magic brand and the bag I have now was 12 quarts for $6.99. Not greater Seattle where I'm sure Black Magic is available too, but I picked it up at Bark and Garden Nursery in Olympia where they carry a range of products in Black Magic and Gardner&Bloome for container culture.

  • morz8
    9 years ago
    last modified: 5 years ago

    Darn, sorry - I'm forgetting with some log in issues lately I'm having to manually enter my zone when I post or no one knows where I am.

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    I get the large bags of pumice at the Indoor Sun Shoppe in Fremont. The UW gets it by the truckload from some trucking outfit in Tacoma that delivers gravel, bark, etc.
    - Tom

  • greenman28 NorCal 7b/8a
    9 years ago
    last modified: 5 years ago

    Bark is not a sucker of nitrogen, exactly. *Sap-wood,* which breaks down rapidly, is a sucker of nitrogen.
    Bark, the outer layer of the tree, is quite durable and serviceable for 1 - 3 years in a properly made mix.
    In fact, as others have said, bark will last for a longer time than would be prudent to go between re-pots.

    I work with bark-based and mineral-based soils exclusively.


    Josh

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    Hi Josh. :)
    I sure agree that sapwood (a common ingredient in mass-produced mixes that claim "bark") can be a sucker of nitrogen. However bark is, exactly, a sucker of nitrogen right from the start, as has been show in several controlled studies. At a 500:1 carbon:nitrogen ratio there is no way it could not be.
    There is only one group that I know of that often grows exclusively in bark, not a bark mix: orchid growers. It is well known there that straight bark requires much more nitrogen to grow in, hence all the commercially available orchid fertilizers at 30-10-10 for bark-only culture.

    Your estimate of up to 3 years for a bark-included mixes does not apply to any that I know of, and I have tried many, including mixing my own. The water retention is drastically different at the end of year 2 vs. what it was on day 1. They are only good for 1 year in my experience. May I ask what brand you are using?
    Bark mixes have another condition that can often lead to over-watering: that is that they are literally the worst of all soil types at tranferring water throughout the mix. In typical plastic or glazed pots, water is exiting quickly through evaporation at the top surface, and a higher quality mix has ingredients that transfer that moisture from the bottom to the top to make it fully available and to limit that sour, rotted, anaerobic soil at the bottom of the pot. TBK peat is best I know of at transferring water within the mix. It's much easier to tell when the plant is ready for watering. :)
    - Tom

  • Embothrium
    9 years ago
    last modified: 5 years ago

    The wholesale rhododendron farm I worked on around 1980 (I guess) potted the rooted evergreen azaleas cuttings into pure fine grade bark mulch for growing on into gallon pot size plants. Regular liquid fertilization with an injector was part of the regimen after potting up.

  • greenman28 NorCal 7b/8a
    9 years ago
    last modified: 5 years ago

    Hey, Tom!
    In truth, peat moss and bark are about equally hydrophobic at first.
    However, bark will dry out sooner than peat moss, which returns oxygen to the root-zone.
    In addition, bark is durable, as opposed to the fine, pre-collapsed peat moss particles.

    I use Orchid Bark and GreenAll Micro Bark (both produced by E.B. Stone).
    The bark is Fir Bark....but Pine bark would be even more durable.

    When I make a mix, I use Bark as the base. To this, I add grit: Pumice, Perlite, Turface, quartz gravel.

    I grow Hoyas, Christmas Cacti, and Orchids in nearly pure bark, indeed;
    but I also grow Maples, Conifers, and Citrus in bark-based mixes.
    My fertilizer is a 3:1:2 ratio, and includes the minors.

    Overwatering and nitrogen-binding are never an issue, nor do my containers have perched water
    in the bottom. By screening the mix of fine particulate, I ensure open drainage/gas exchange.


    Josh

  • Embothrium
    9 years ago
    last modified: 5 years ago

    Baled fine peat is supposed to have been subjected to an intentional, serious drying process. That's why it repels water. Water will go right into bark, baled fine peat has to be soaked slowly, with some effort to get it moist again. Warming the water used has been said to improve results.

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    Josh, hydrophobicity (is that word right, lol?) in peat & bark are technically similar, yes, (bboy they are only similar because the water must actually penetrate the bark surface for storage) but that is only for the raw ingredients. Those same rates you looked up do not apply to a high quality peat-based mix, which is never really hydrophobic. They also do not apply to higher-quality, longer-fiber peat like TBK.

    I like the diversity in your mix, but if we want to compare it to peat based mixes we have to fix the apples/oranges thing so we're on the same scale. When you say that "bark will dry out sooner than peat moss, which returns oxygen to the root-zone", that is true, but a very simplistic approach that doesn't show the whole picture. You have a very xeric mix, and my base mix is more appropriate for the most thirsty tropicals in full sun. Both can be fine-tuned to hold more or less water, which then inversely affects how much air the mix can hold. I could make a nice porous wonderful-drainage mix by putting 3 rocks in a pot and calling it soil. The real trick comes in getting it to hold BOTH air and water in superior quantities.
    So if we each custom mixed our ingredients to match in either air or water holding capacity, then you would see that the peat has the ability to excel bark at any specific balance point of both, except perhaps in the case of a specialized pure-cactus mix.
    You said you grow orchids in pure bark, as have I. If you have anything similar to conditions that orchids like, and have real experience, then you do know that if you don't repot every year, and try to stretch it to 2 or 3 years in bark, then when you repot you'll see the roots in a big hollow ball around the outside, with a hollow core that is rotten out. That's why many of the commercial phal growers have switched to long-fiber sphagnum, even though it's more expensive than fir bark. It transfers the water away from the wet core to the dry surface much better.
    So drainage/air in the mix is relative to water-holding capicity, since a peat-based mix can be made as porus as you need it. Peat can hold more air and water than bark.

  • greenman28 NorCal 7b/8a
    9 years ago
    last modified: 5 years ago

    Ah, but you see, Turface, Pumice, and Perlite do hold moisture...but they also maintain structure.
    Instead of fine peat particulate, I increase the bark dust component in my mixes for plants such as ferns.
    Bark dust is superior to peat moss in that it isn't pre-collapsed. Bark has a longer container life.

    Peat moss is hydrophobic when dry, and hydrophilic when wet.
    In general, its use is best limited to a small fraction of the overall mix.
    Some folks use one part peat moss, one part perlite, and five parts bark to
    create the mix called the 5-1-1. This mix, truly, is best for a single season.
    It holds much more moisture, and yet it is difficult to over-water.

    Do you have experience growing in bark and grit-based mixes?
    If so, what sort of bark were you using, how much sapwood did the product include,
    and what was the average particle size of the bark? (i.e. was it screened to size?).

    Incidentally, I just re-potted my Orchid, which had been in long-strand Sphagnum.
    The Sphagnum held way too much moisture and had nearly rotted out the roots.
    It's in a proper Orchid pot now, in a mix of bark, turface, and pumice,
    with a pinch of Osmocote.


    Josh

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    "Ah, but you see, Turface, Pumice, and Perlite do hold moisture"
    I am sorry, but this is irrelevant. They do hold water, but what is relevant is how much in comparison to other media. Generally considered "drainage" components, they are literally not even in the same ballpark as peat at holding water. Turface, for instance, (I like turface as a drainage ingredient) can hold one-times it's weight in water. Regular peat can hold 20 times that, and blond peat even more.

    "Peat moss is hydrophobic when dry, and hydrophilic when wet"
    Again, I am sorry, but this is irrelevant, as we are talking about high-quality mixes that contain peat, which are not hydrophobic in normal use; and not about plain peat for a growing media.

    "...called the 5-1-1. This mix, truly, is best for a single season"
    With respect, you honestly don't have the experience to be making a blanket claim like that. I looked you up. ;)

    "It holds much more moisture"
    No, the 5-1-1 does not hold more moisture than peat mixes or mine specifically; not even close. In fact, it holds so much less that it is like comparing apples to oranges again. Even its creator, tapla Al, talked about a 'commitment to watering', which is why you will never see a mix like this, that needs water more often, capture any significant portion of the retail potting mix market. They are intentionally tuned to have less frequent watering to reflect consumer desire & ability.

    "Do you have experience growing in bark and grit-based mixes?"
    I've grown in bark & bark-based media for 25 years. I still have a few cubic feet each of 3 different sizes of pure Fir Orchid bark in my supply room that I still use in one of my orchid mixes for smaller plants (especially paphiopedilum), and also for Rhodie-family plants. I have tried almost every brand you can imagine of over-the-counter potting soil, most of which contain bark & "forest product" (lots of sapwood). I did fertilizer experiments in the early 90's that showed me it was very important to use a full-spectrum fertilizer with minors when growing in bark & mineral (low organic) media. I have mixed my own bark-based potting mixes, usually using orchid barks as the base and mineral drainage components similar to yours, mostly in the 1988 to 2000 range.

    "my Orchid... The Sphagnum held way too much moisture and had nearly rotted out the roots"
    I don't know if it was the medium. :) How about the hundreds of thousands that are grown in pure long-fiber sphagnum for mass-market sale in grocery stores all over the country? Here is one of mine in pure long-fiber sphagnum that sits all year in my living room. It hasn't been repotted for 8 years. It is sending out a second spike now:

  • Embothrium
    9 years ago
    last modified: 5 years ago

    Again we see that dissecting other posters instead of the topic contributes nothing.

  • greenman28 NorCal 7b/8a
    9 years ago
    last modified: 5 years ago

    Tom, I don't believe I attacked you or called your growing experience into question.
    So why are you laying on with the ad hominem attacks? It seems a rude introduction.
    I haven't "looked you up," so I'm not sure who you are or how seriously you take yourself.
    If you feel threatened by something I said, I do apologize.

    Secondly, mass-market potters use peat-based media for reasons of profit...not plant health or longevity.

    But I digress. I think you're missing the point. I avoid peat because it holds too much moisture.
    There's simply no need for it when superior filler ingredients are available.

    Now, I admit, in many parts of the country, good bark is not readily available;
    and so, in those regions, compromises will have to made.

    Excellent, so you're familiar with Al (Tapla)! I'm interested in sharing information,
    and so I wanted to share this (by Al):

    "Bark fines of fir, hemlock or pine, are excellent as the primary component of your soils.
    The lignin contained in bark keeps it rigid and the rigidity provides air-holding pockets
    in the root zone far longer than peat or compost mixes that too quickly break down to a soup-like
    consistency. Conifer bark also contains suberin, a lipid sometimes referred to as nature’s
    preservative. Suberin, more scarce as a presence in sapwood products and hardwood bark,
    dramatically slows the decomposition of conifer bark-based soils. It contains highly varied
    hydrocarbon chains and the microorganisms that turn peat to soup have great difficulty
    cleaving these chains."


    Josh

  • gardengal48 (PNW Z8/9)
    9 years ago
    last modified: 5 years ago

    I find it somewhat amusing that in his original post, grrrnthumb asks for a critique of his container soil mix, yet when various critiques are presented, he does his best to refute them. What's up with that? Did you really want any critique at all or were you just trying to promote a container soil recipe that you created and have found useful? Nothing at all wrong with that - we all like what we like and are comfortable with - but maybe we should leave it at that and keep the request for a critique out of it.

    FWIW, I know of a great many container gardeners whose experience and preferences have lead them to focus on a bark-based mix with a minimal amount of peat or compost as a component. Typically they have arrived at this combination because they have found that its durability and porosity are maintained better and longer than those mixes that have heavy proportions of peat or compost or other less durable components. Whether or not ALL container gardeners are inclined to follow this route and adopt watering and fertilizing regimes that support this medium is surely more of a personal choice than not and less related to the 'science' behind the medium structure, although I think the science is also pretty well -established in this regard as well. Container gardeners who do develop their own mixes tend do so simply because the vast majority of packaged retail mixes on the market simply do not offer the qualities they are looking for. And also for cost savings :-)

    As one who gardens almost exclusively in containers, my experience has lead me to the bark-based, 5-1-1 mix (with a few add-ons) as being the best for my needs. It is by far more durable than any peat based mix I have encountered and offers both the free drainage and water retention my long term container plantings require. I also opt not to use any organically sourced fertilizers for my container plantings as these tend to be rather inefficient in delivering nutrients under these conditions. Whether all container gardeners would opt to use a similar mix with a similar fertilizing and watering regime depends on their needs and plant requirements and how much effort they care to expend. YMMV.

  • Embothrium
    9 years ago
    last modified: 5 years ago

    Bark based mixes are frequent in commercial production. While I'm not saying erroneous practices are not present in large scale, for profit growing operations - prime example failure to prevent circling, kinking and binding of roots - if bark was fundamentally unsuitable it would not be used. Even bark tends to turn to muck when plants in fertilized, watered containers are left in it for sometimes not all that long of a time. Using peat instead we start out with a material that is partly decomposed right from the beginning.

    There are, of course, some crops and conditions where a retentive mix is found to be desirable. Careful irrigation management might make it possible to minimize water use by combining this with comparatively dense mixes. A down side to using a less generally familiar approach is final consumers having problems managing the plants after they get in their hands. Perhaps this comes up most often with florist pot crops.

  • tapla
    9 years ago
    last modified: 5 years ago

    Invited over to the conversation, I would offer something for your consideration. There are two ways to look at container media. One is from the grower's perspective, which is heavily laden with grower convenience, and the other is from the plant's perspective - let's consider that from the perspective of vitality and growth.

    The grower wants something easy and something he feels really good about for a variety of reasons. In the original post at the top of the thread, the poster feels really good because he's trying to cover as many bases as he can. The issue I see here is he can cover the same bases more effectively with a simple soil and a good, regular nutritional supplementation program. A quick look at the list of ingredients leaves me feeling that I could do much better concentrating on making sure the balance of water/air retention was as good as it can be and that it will stay that way for the intended life of the planting OR the interval between repots (different than potting up), then turning my attention to nutrition.

    The reason I say this is because the volume of fine ingredients in the soil ensures a considerable perched water table, which is always a negative after you exclude grower convenience. I know - sounds like a broad statement, but we can discuss it,

    You can't take a volume of fine particles and amend it with larger particles and expect either the height of the PWT or drainage characteristics to change noticeably. You CAN reduce the total volume of water the medium is capable from holding, but that doesn't erase entirely the negative effects of a PWT.

    A copy/paste from one of my other offerings:

    "If you start with a water-retentive medium, you cannot improve it's aeration or drainage characteristics by adding larger particulates. Sand, perlite, Turface, calcined DE ...... none of them will work. To visualize why sand and perlite can't change drainage/aeration, think of how well a pot full of BBs would drain (perlite), then think of how poorly a pot full of pudding would drain (bagged soil). Even mixing the pudding and perlite/BBs together 1:1 in a third pot yields a mix that retains the drainage characteristics and PWT height of the pudding. It's only after the perlite become the largest fraction of the mix (60-75%) that drainage & PWT height begins to improve. At that point, you're growing in perlite amended with a little potting soil.

    You cannot add coarse material to fine material and improve drainage or the ht of the PWT. Use the same example as above & replace the pudding with play sand or peat moss - same results. The benefit in adding perlite to heavy soils doesn't come from the fact that they drain better. The fine peat or pudding particles simply 'fill in' around the perlite, so drainage & the ht of the PWT remains the same. All perlite does in heavy soils is occupy space that would otherwise be full of water. Perlite simply reduces the amount of water a soil is capable of holding because it is not internally porous. IOW - all it does is take up space.

    If you want to profit from a soil that offers superior drainage and aeration, you need to build it into the soil from the start, by ensuring that the soil is primarily comprised of particles much larger than those in peat/compost/coir, which is why the recipes I suggest as starting points all direct readers to START with the foremost fraction of the soil being large particles, to ensure excellent aeration. From there, if you choose, you can add an appropriate volume of finer particles to increase water retention. You do not have that option with a soil that is already extremely water-retentive right out of the bag", or one that you build with the largest fraction being comprised of fine particulates.

    Considerable experience and success maintaining plantings in containers for both short and the very long term has left me with the conclusion that I'm better off considering container media from only the structural view. Nutritional supplementation is very easy in containers and VERY different from the way we approach it in our gardens. Container culture is much more like hydroponics than it is growing in the garden, so maintaining the attitude that it IS quite different will leave our minds open to different approaches.

    From the plant's perspective, well-aerated soils that drain well combined with frequent apps of soluble fertilizers that have ALL the essential nutrients in a ratio close to what plants use, as well as in a ratio favorable to that of the other nutrients in the fertilizer is hard to beat.

    Most arguments about these statements don't center around their efficacy insofar as producing great plants, but in how they conflict with grower convenience and grower ideology. It's important to realize what perspective you're arguing FROM if there is dissent; the reason being that ideologies are self-limiting by their nature, and grower convenience vs what's best for the plant are often mutually exclusive; the perfect example being that there is greater potential for plants to grow closer to their genetically endowed level of vigor in media that don't hold perched water than in media that does, but the trade-off it they require more frequent watering. Arguing that your plants would die because you can't water every other or every third day instead of once per week is arguing from the perspective of grower convenience.

    Growing is about compromise, but what's most important is being able to recognize potentials and to envision what we're giving up for the compromises and weighing that against the effort it takes to pay for the gains. There are a lot of variables in discussing container media, but a lot of soil science is pretty concrete and settled. It's how we combine not only the ingredients, but the various perspectives that dictate the ingredients that leaves us with what we'll ultimately grow in.

    There is probably no 'right or wrong', and even discussions about 'better or worse' can get dicey because of the various ways to view soils (convenience, ideology, plant's perspective). I think the best way to look at soils is from the plants perspective and to realize that to deviate from that perspective for whatever reason is part of the compromise I mentioned earlier.

    That's the view from here. Good discussion - if we can keep the tempers in check & keep focused on the topic. ;o)

    Al (Who's a long way from home.)


  • Embothrium
    9 years ago
    last modified: 5 years ago

    Growing plants in the ground is hydroponics also, strictly speaking roots of plants grow in the air and water between soil particles rather than actually in the soil itself. So many plants will not grow in dense, heavy soils because there just is not enough air space for their needs. In the extreme shade and highly decomposed soils of the climax tropical rain forest the majority of small plants grow on trees instead of in the ground. When attempting the smallest, highest altitude alpine plants in containers it may be necessary to have effectively no visible clay in the potting medium in order for these to thrive.

  • tapla
    9 years ago
    last modified: 5 years ago

    I'm pretty sure splitting hairs about whether or not growing in the garden is 'hydroponics' wouldn't be germane to the conversation, so I'll avoid the topic. Generally speaking, I think most people regard hydroponics as a method of growing plants, using water/mineral solutions and sometimes an inert medium. I guess my point in that regard is/was that on a scale of 1-10, with 1 being growing in the gardens and beds, and 10 being full hydroponic growing, conventional container culture rates about a 7-8 on the scale ..... quite different than growing in in situ mineral soils.

    If the rest of the offering was to illustrate that sufficient air is a critical requirement of container media, I agree and have assigned the idea near mantra status in my travels, as is amply illustrated in my post previous. I believe building adequate aeration into the medium, in such a way that the medium remains adequately aerated for the intended life of the planting or interval between repots, should be our most important consideration when building our media, next perhaps to phytotoxicity. This is, of course, from the perspective of our ability to offer the greatest potential for growth/vitality.

    Al

  • Embothrium
    9 years ago
    last modified: 5 years ago

    Would that be splitting of root hairs? All your "rebuttal" demonstrates is that you missed my point.

  • tapla
    9 years ago
    last modified: 5 years ago

    It's true, in all honesty I did miss the point. I had a lot of trouble discerning how anything you said related to what I said, other than the part about hydroponics, which I disagree with, but chose not to make an issue of. (I'll take the blame for missing the point in hope that perhaps the conversation could be steered in the direction of light rather than heat.)

    Al

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    Gardengal I'm sorry if I wasn't clear enough in my first post. I was most interested in a critique of the fertilizer and lime. As I mentioned early on, I am pretty happy with the major components. I am however very glad to hear all critiques you have of the whole mix; I just hope you don't mind me discussing them in return. :)

    Josh the last thing I want to do is personally attack you. :) I was under the impression that if you make multiple experience arguments (authoritative opinions pitched as facts, but without explanations), correcting me on things I have supported above with facts, then you have made your experience an issue yourself, but I am sorry I offended you. I do promise to try and be more polite. :)

    Bboy you mentioned that bark mixes are sometimes used without apparent problem commercially. 1) They are usually working on a turn-around of less than a year in that mix before repot or sale, and 2) they have commercial maintenance with automatic or paid watering, and automatically dosed fertilization, which we don't have, that let them reasonably grow hydroponically (in the sense that we usually mean it). If commercial use were an indicator of an effective mix, then peat of course would be king by an exponential factor. I appreciate your point about consumer problems managing plants with an unfamiliar approach.

    Al, welcome to the conversation! I am glad you are here. We may like different mixes, but I think we actually agree on many things. For instance, I also mentioned way up above that these type of bark mixes are similar to growing hydroponically. It is much more important in bark to carefully maintain your plant's nutrients through a consistent, comprehensive fertilizer regime, and not rely on the soil. We also agree on how much more watering bark takes; I'm glad you mentioned watering every second or third day (sounds crazy to me, but at least we agree how much more work is involved). We also agree here that my mix is tuned towards the needs of the grower instead of exclusively the plant (I'm not a plant, lol!).
    Regarding your revolutionary contention that perlite & pumice can not add drainage to peat (overturning a universal tenant in soil manufacture)... I do understand your theory (for instance sand added to a clay soil for lawns is worthless until it is the main component), but in actual practice it doesn't work as you've described. For instance, if you were to compare water-pour-through rates for my drainage version soil vs. plain peat, even after years of use, there is no comparison. Those extra components do add quicker drainage in real life.
    Drainage though is a bit of a false goal, or a goal based on an assumption. What we really want is to partially dry out the core of the mix at intervals between watering, which prevents that sour core-rot where roots won't live. Surely drainage helps and is good generally, but you are assuming it is the only way. Al I've seen in your other posts where you refer to capillary action of soils as a negative. I couldn't disagree more. Capillary action is the savior of a soil mix; it's the vehicle that brings wet core water & water from the perched water table you described up to the drying surface, and balances moisture throughout the pot. It eliminates the perched water table. Peat has it and bark doesn't.
    It's odd you were referring to the "perched water table" as applying to peat because of its small particle size. I believe you misinterpreted the original research on that: it was done on bark and applies to bark. Later authors quoting the research were much more vague about the fact that it referred to bark, and I could see how it would be an easy mistake. So if you are growing in medium grade or finer bark, and you don't have enough of peat or coir or similar to make a full capillary wick, then you DO have a perched water table, and the original research was about helping you work around it. (taller pots, no drainage material at the bottom, etc.). Here is a link to a page that explains a portion of that research at Oregon State University. So when Josh up above says he doesn't have a perched water table, that's a misunderstanding of the term in relation to the research you are relying on, bark in containers does have perched water because of its inferior wicking ability.

    Here is a graph from Organic soils and peat materials for sustainable agriculture by Parent and Ilnicki (2003) that shows a hint at what I was talking about regarding peat holding more air AND water. Look at the 2nd & 3rd lines:

    It's not fair of course to directly compare a drainage peat mix straight across to a peat mix with the most water retention, since neither bark nor peat mixes have a fixed level of water retention they must be mixed at. Both can be mixed wetter or drier, with a large overlapping range. When you do mix them to match in either air or water, you can see, as in the graph above, that peat is more efficient at any combination of both air and water holding power.
    More later. :)

    - Tom

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    Sorry, in that last paragraph a typo, meant to say it was not fair to directly compare a drainage bark mix straight across to a peat mix with the most water retention.

  • greenman28 NorCal 7b/8a
    9 years ago
    last modified: 5 years ago

    Hey, Tom, thanks for the reply.

    After I screen my bark, I am left with excess bark dust particulate.
    This dust is similar in size to peat moss. For plants that require more moisture retention -
    ferns, for example - I add a portion of the bark dust back into the final mix. This takes the
    place of peat, by bridging the gaps between particles, and regulates the moisture of the whole soil.

    When I look at the drain holes of my containers, I can see that there is no saturated
    layer at the bottom. If I tip the container 45 degrees, no excess water runs out.

    Eventually, the bark will decompose, and the particles become smaller and smaller.
    At such a point, the mix does begin to support a perched water table,
    and a re-potting is required.


    Josh

  • Embothrium
    9 years ago
    last modified: 5 years ago

    1) They are usually working on a turn-around of less than a year in that mix before repot or sale, and 2) they have commercial maintenance with automatic or paid watering, and automatically dosed fertilization

    Neither statement is true. Go look at some nursery stock at a garden center, most of which is sold to homeowners and other small scale users, for planting out under the conditions they will have.

    Bare-rooting at planting time has emerged as an often superior method due to the disparity between the textures of container media used in commercial production facilities and of the soils encountered by plants on the final planting sites. When knocking plants out of pots to plant them out I encounter bark-based container media over and over.

    In addition to the pure bark being used by the wholesale rhododendron farm I worked on decades ago a retail growing operation (more kinds of plants, in smaller numbers of each) I became involved with much later was potting in bark and sand, with fertilizer added. Dryland plants got more sand than other kinds.

  • tapla
    9 years ago
    last modified: 5 years ago

    Hi, Tom

    After I scanned your article, the first thing I did was follow the link to the OSU research you cited. As I read through it, I didn't see anything different than what is contained in an article I wrote back in '94. The wording and discussion is actually so close to what I wrote, that I tried to find out whether that article was written after mine.

    I think that initially, adding a small fraction of perlite pumice, Turface, things that you usually consider as drainage material to a large fraction of peat, increases drainage, but only until the peat compacts/nests around the 'drainage' material. Perlite is normally included in commercially packaged soils at less than 10% of the whole. Doubling its presence isn't going to increase drainage or reduce the ht of the PWT, though it will reduce the total volume of water the medium is capable of holding.

    Illustration: start with 10 parts of fine sand that supports a 4" PWT. Add 1 part of BBs. Does the flow through rate change? How about the ht of the PWT or volume of air in the medium? Technically, on a per volume basis, there is a decrease in the % of air in the sand/BB mix compared to only the sand w/o BBs. All that changes is the 'volume' of water in the PWT. Peat may be slightly different because it's interlocking fibers may not compact to the degree that sand will, but remember that the fiberosity exhibits the same properties whether or not there is drainage material present. If peat compacts when there is no drainage material, it will still compact when there is.

    In order for drainage material to improve flow-through rates, it has to affect gravitational flow potential. In order to do that, it must great pockets where water molecules can adhere to themselves, increasing their collective mass. These large droplets then depend on cohesion to keep them together as gravity acts to move them down and out of the container. If drainage material can't create 'puddles and channels' within the media, it's not going to be effective.

    I want to comment on some of the things you mentioned as though we're conversing, so I'll make your offerings bold and my reply will be in default type:

    Drainage though is a bit of a false goal, or a goal based on an assumption. What we really want is to partially dry out the core of the mix at intervals between watering, which prevents that sour core-rot where roots won't live.

    My focus has always been on aeration, though I recognize the direct/converse relationship between drainage and aeration. The soils I build and suggest are based on the assurance that they will retain ample volumes of air for extended periods - that they are structurally sound. Of course, drainage automatically comes along for the ride.

    I don't think I would say "What we really want is to partially dry out the core of the mix at intervals between watering". My view is that there is no 'core' to speak of, because water that is not tightly bound to or in media particles moves down to occupy the PWT, which is actually the bane of most commercially prepared container media. Moisture locked in and on soil particles situated above water in the PWT moves quite freely through media by diffusion, so there is never a saturated 'core', only the PWT if the medium supports one. What we really want, is for the PWT to disappear as fast as possible, so a favorable volume of air can return to the soil ASAP.

    Roots in soggy media begin to die very quickly, often within a few hours or less at temperatures above 60-65*, so PWTs are a decidedly bad thing. Remember please, that here we are looking at media from the plant's perspective. I acknowledge that a PWT can be a necessity to accommodate our ability or our prioritization in terms of how often we can water, but that doesn't change the fact that media that do not support a PWT and need more frequent watering offer greater opportunity, within the limits of other cultural factors, for plants to grow to their genetic potential. That's an important consideration, because if we knowingly use a soil that supports a PWT because it's more convenient, we are sacrificing some degree of growth and vitality on the altar of that convenience. I try to build my soils to maximize water retention and still have no (or very little) perched water.

    The cyclic death and regeneration of fine rootage exposed to the anaerobic conditions of media that support PWTs is very expensive from the perspective of energy outlay. Energy that might have gone into blooms, fruit, foliage, or just increasing biomass, must be directed to root regeneration subsequent to each time we dare allow our planting to be irrigated to container capacity.

    Surely drainage helps and is good generally, but you are assuming it is the only way.

    I think you can see from my offerings that how I approach container media is more complex than only a single narrow perspective would allow.

    Al I've seen in your other posts where you refer to capillary action of soils as a negative. I couldn't disagree more. Capillary action is the savior of a soil mix; it's the vehicle that brings wet core water & water from the perched water table you described up to the drying surface, and balances moisture throughout the pot. It eliminates the perched water table. Peat has it and bark doesn't.

    I've never referred to capillary action as a negative. It just is what it is - the product of adhesion + cohesion - no more friend or foe than gravity or diffusion, which is something you didn't consider. Plants absorb water a molecule at a time, and water readily diffuses in media of large particles due to superior gas exchange. Here again, it's kind of a personal choice. You may prefer a soil with good wicking capabilities, but along with that comes the fact that the better they wick the more perched water they support. I, on the other hand, prefer a soil with good gas exchange (diffusion) and no PWT. The price I'm willing to pay is a strengthened watering can arm. ;o) Bark and peat feel dry to the touch when they reach about 40% moisture content, but plants can still extract water from media particles down to about 30-25%, so 'feels dry' isn't necessarily dry. There's a cush there.

    I understand what's required for wicking SWCs and how water retention in wick-irrigated media varies from media watered from the top, so we can save that talk for another time.

    Water starts to perch in containers when the soil particles are something just a little larger than .1". As particle size decreases, the ht of the PWT increases inversely. Whether or not bark holds perched water depends on it's size. Obviously, bark the size of Sugar Pops will hold no perched water, but bark ground to the consistency of peat will. Peat may initially hold more air and water than composted bark, but we all know that compaction is a considerable issue for peat; and conifer bark breaks down at roughly 1/4-1/5 the rate of peat, all cultural influences equal. I point to the fact that I always suggest partially composted or uncomposted bark in the soils I use, in sizes up to 3/8" to ensure no or minimal perched water. The grower can then add finer particulates as he/she sees fit to adjust the water retention of the media. When you start with fine particulates, it's very difficult to amend them to increase drainage/aeration, though as noted above, you CAN add materials like perlite that decrease the volume of water the soil can hold.

    It just makes more sense to me to approach this from the perspective of building a soil that holds no perched water, but is capable of holding an adequate volume of water in micro-pores, leaving macro-pores largely open, than it is to adopt a soil that, at container capacity, always has a significant fraction of available macroporosity clogged with water.

    Again, it has much to do with trade offs and what we are willing to do insofar as watering frequency (convenience), but the more highly aerated soil with better gas exchange, which occurs partially because we need to irrigate more frequently, offers better potential.

    I've grown extensively in both, and if the results weren't significantly better, I'd probably still be growing in a peat or compost-based soil.

    As always, YMMV. Good talking to you Tom.

    Al

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    Al, who is Butch Ragland? Is he a friend of yours? He also takes credit for writing your article. They are basically the same with only minor wording changes. One was obviously copied from the other. I'm a little confused??
    Either way though, it is not referencing any real science. I don't think we can put it on the same level as Professor Altland's work (a world-wide leading scientist on bark in container soils) which was based on real, original scientific research. Here is one major difference in his article from what you are saying: You still aren't grasping what a perched water table is. You and Josh are expecting that since you have apparent drainage without standing water then you must not have a perched water table. That's not correct.
    Perched, in this context, does not mean a "very" wet layer of soil. It means a layer that "stays" wet. It means a significant difference in moisture from the top to the bottom. Peat's capillary action spreads the moisture around & up the pot, rotates it between wet-dry, wet-dry; so it is not "perched", even if it starts out with plenty of moisture. Bark, although it does hold less water if not part of a mix, does not have that capillary action, and it does perch water at the bottom of the pot. I'll say this very important point again: the original research was done on bark, and pointed to ALL bark pots (yours too) as having perched water, not peat. I did look hard, but if there is real research applying this also to peat, then please do show me where (not just a theory as to why). Here is a visual from the page I posted before showing the saturated bottom layer in a container using bark. These are amounts of water:


    Here is another visual from that page that shows how the research found that container height did not affect the size of the perched water table at the bottom of containers (bark):

    Below is another specific chart showing perched water in both fine & medium grade Douglas Fir bark from this article expounding more on the original research by Gabriela Buamscha (on Douglas Fir Bark), that also talks more about perched water tables for all bark in containers. These represent pots and show the higher water levels at the bottom:

    Here is a link to more original research by James Owens at Oregon State University, published in Horticultural Science, that shows the nitty gritty details regarding perched water tables in Douglas Fir bark. Here is an additional quote from their conclusions:

    "Most agree that AS [air space] should be from 10% to 30% (Yeager et al., 2006). Considering most propagation material planted into 2.7-L (#1) containers (typically 15 cm tall) will have root systems that reach 2 to 4 cm deep, AS may be too high and water retention low in the substrate accessible by these roots early in the production cycle. This can lead to difficultly in maintaining needed substrate moisture content for liners, transplants, or seedlings."

    This partially addresses your idea that it's better to grow tropicals in a cactus mix and just buck-up and water more often. It's not a normally expected reasonable level of watering commitment for non-paid hand watering in one's home. But I sure am jealous you have the time to do it! :)
    - Tom

  • tapla
    9 years ago
    last modified: 5 years ago

    I have no idea who Butch Ragland is. I wrote my article in '94, subsequent to a conversation with a geologist, during which I connected the similarities regarding the phenomenon of geologically perched water tables with what I observed happening in the heavy, peat/compost/coir-based soils I was using at the time. I did a fair amount of research to make sure I was intimately familiar with the physics, but I can assure the words are mine, and mine alone. The only thing I had help with in putting it together was borrowing some phraseology - 'gravitational flow potential' for example.

    I read all your links thoroughly, and found not a single thing that contradicts or disagrees with anything I've put forth as it relates to water movement/retention in substrates.

    If we have a semantic difference, I'll explain perched water as I understand it. Water is perched in a substrate when the capillary attraction of the soil particles and container surfaces combined are greater than the gravitational flow potential of the water column. This creates a 'puddle' at the bottom of the container that fills all air pores contained in the substrate below the line of equilibrium between the forces I mentioned (capillarity and GFT), which determines the height of the PWT. This height of the PWT is determined almost exclusively in direct relation to substrate particle size.

    You cannot say that bark does or doesn't support perched water unless you include reference to particulate size. Substrate particles can and do hold water tightly bound within intra-particulate pores, and movement of this intra-cellular water, but it is inter-cellular water that occupies potential pores between particulates that is of particular concern and what causes the anaerobic conditions that affect root function/growth/metabolism.

    You're misreading or misapplying the data you're asking me to consider. I agree with it all, and it agrees with all I've said. Sorry.

    The one point you make that is valid is one I often address. That is, in very porous substrates, the upper portion of the container often dries quickly. I didn't see you mention it, but bark actually has greater capillary attraction than peat, and the simple reason is because intra-particulate pores are smaller. The problem is, water has to move from particle to particle, and because of the larger particulate size, there is less contact between particles to provide a conduit through which the water can move between particles. Compounding that issue is the fact that high porosity also means increased gas exchange and more rapid evaporation - especially in the upper reaches on the container. The result is, even though bark has greater capillary attraction, water moves through bark so slowly and the larger bark particles increase gas exchange to the degree that the water either gets used by plants or passes out of the soil in vapor form vaster than it can be replaced.

    I said I've addressed this issue many times by suggesting more frequent irrigation until the root system is established. In my estimation, the added effort it takes to water a little more frequently that accompanies the porous soils far outweighs the negatives associated with a soggy soil.

    Al

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    Well I'm glad it was you who wrote it then. You might want give this guy a hard time about plagiarizing it, here. Says he even gets paid to give talks on it!

    I find this statement shocking:
    "I read all your links thoroughly, and found not a single thing that contradicts or disagrees with anything I've put forth as it relates to water movement/retention in substrates".
    I gave you several examples of empirical, numerical, scientific proof that your own pots of medium-and-finer grades of bark are holding perched water and you don't see anything that conflicts with what you've been saying? And those articles did specifically reference particulate size & grade of bark, read them again, it's even in that last illustration I included above.

    One way to look at the differences is to say, like you did, that you just have a "different" definition of perched water than container soil scientists. Another way to look at it is that you just don't understand perched water because your interpretation doesn't have any science to back it up. I'm flabbergasted that you still refer to peat as having perched water. Prove this. You're just working off a theory, Al. Show me the numbers like I've shown you. Perched water tables, even in geology, are "parked" "stopped" "trapped". It doesn't matter how wet peat gets if it is still able to distribute & drain the water through capillary action.

    Speaking of capillary action, that's another thing you don't understand. Your idea that bark has more capillary action than peat, even if it were true, would only apply to one "piece" of bark, not bark plural. It would be completely irrelevant since we do not pot on a single piece of bark, we use bark plural. So it is only correct to say in this context that bark has no capillary wicking ability, as is evidenced by the science I referenced proving the exact amounts of perched water in Douglas Fir bark when used in containers.
    Your third paragraph is again wrongly equating peat's wicking ability to that of bark. The puddle near the bottom of the pot is only perched, it only stays around, when the media does not have the ability to wick it away. This applies to your bark, not peat, and so a statement like "This height of the PWT is determined almost exclusively in direct relation to substrate particle size", has obviously been borrowed from a bark-only article, otherwise you would understand that it can't be true because of the massive differences in capillary ability between peat & bark.
    Btw, you are talking about capillary "attraction" of water to your bark pieces and to the pot. That should really be just adhesion & cohesion, not capillarity. Capillary is when those same forces are used to move the water uphill or sideways (peat's got it, bark don't) against the force of gravity (couldn't you just say gravity instead of Gravitational Flow Potential?).
    Anyway, Al, I know my typing doesn't often sound as friendly as it does in my head, so I hope you'll forgive me if that's true here. I really have enjoyed discussing this with you. :)
    - Tom

  • tapla
    9 years ago
    last modified: 5 years ago

    The linked you provided is without doubt my work. I cannot say it is plagiarized, because I have often given permission to use my work in books and other publishings, but it is ALWAYS with the understanding that I'm given credit. I registered at that forum and will investigate further. I'll demand that the material is removed or that I'm given credit, but I'll have to look around the forum site and see who best to approach. I'll be aggravated if I find permission wasn't sought. It IS possible that he did contact me for permission, but again, at least a couple dozen requests have been made to use the article, so I don't remember. The article was published a couple of years ago with minor modifications in The Journal of the American Bonsai Society, and not long ago in a major Texas city newspaper, though I forget which it was.

    You haven't read all I've said (over and over in other conversations), and are insinuating that I have disagreed with the fact that medium and fine grades of bark hold perched water. I NEVER said that here, or anywhere else at any time. What I DID say is that the ht of the perched water table varies directly with the size of particulates in the substrate. Please don't put words in my mouth and then be shocked at what you think you heard. The large bark that I use is large by design - so it DOESN'T hold perched water, or if it does, it holds very little.

    My definition of perched water is the same as that used by soil scientists and geologists alike. In geology, water can perch in clay strata above sand or gravel, but only if the particle size in the underlying substrate is larger than 2.1X the particle size up the overlying strata. The same holds true for "drainage layers" in containers. A drainage layer CAN be made to be effective if it's particles are less than 2x the size of the particles in the substrate above the drainage layer.

    If you think peat does not hold perched water, fill a clear cup with moist peat and lightly tamp it down to simulate the compaction resultant from watering from above. You will see the perched water table through the sides of the cup. If you still doubt the water is perched water, insert a toothpick through the drain hole and observe the additional water that exits the cup. The toothpick 'fools' the water into 'thinking' the cup is deeper than it is. Actually, the toothpick increases the GFP and the water moves down the toothpick in search of what it 'thinks' is the bottom of the container.

    If peat-based soils are so super and plant friendly, why is it that everyone that has tried the bark-based mixes refuses to return to peat/coir/compost-based soils? It's because they are simply incapable of offering the same potential for maximizing growth/vitality, within the limitations of other cultural factors, that soils comprised of larger particulates can.

    An EXTREMELY productive soil, and one that is VERY conducive to root health is the gritty mix. It consists of equal parts of screened (uncomposted) fir bark, screened Turface, and crushed granite. Because it is 2/3 inorganic, it is extremely long-lasting. Because the particle size is right at the point where the PWT disappears, it maximizes water retention w/o holding perched water. It also is adjustable for water retention by varying the volumes of Turface and granite.

    Just so we're on the same page, please consider my tone throughout the post as conversational too, and not adversarial, though I do get weary arguing the same points and and having my time tied up where nothing seems to get accomplished. ;o)

    I know you'll do whatever you think best, but my opinion is, and my own considerable practical experience, along with the experience of a large group of others I have helped has shown me that you can probably squeeze the best from your plants by starting with a large fraction of a soil component that is comprised of large particles (pine bark in a size range of dust to 3/8") and add some peat and perlite until you have enough water retention to satisfy yourself, keeping in mind that as water retention goes up and whatever you wish to call the puddle of water at the bottom of the container ;o) appears, your compromise begins. Couple that soil with a soluble fertilizer in a 3:1:2 RATIO, and I really think you'll be very pleased with the results. I'm not saying you can't do well with the soil you've described - I just think you can make things easier and increase your potential if you consider what I offered.

    I've tried what you're describing, Tom. I've been studying and tinkering with soils for more than 20 years, and I wouldn't even consider a peat-based soil unless pine bark was unavailable. Actually, the forums are filled with those who have turned the same page as I, and we can't ALL be wrong.

    One last note before I head out - coir is usually not used extensively in commercial media - what I mean is not as a significant fraction of the medium. It's high pH (much higher than peat) makes dolomite unsuitable as a Ca/Mg source if it is included as a significant fraction. It has a potentially VERY high K content, it's loft is less than peat and it compacts easily, so it is generally used primarily in sub-irrigation applications (top watering avoided when it's used); and I'm sure you're aware of its potential high solubles content (salts).

    Oh! Let me know if you'd like to try a bag of the gritty mix, but only if you can commit to watering daily or every other.

    Best luck on your journeys in husbandry, and Happy New Year!

    Al

    PS Not that it's important to this conversation, but I get several e-mails each month like the one below that arrived this evening. I also recently finished helping the equivalent of what would be the Parks and Recreation Dept of an American city, except this was the city of Paris, France, develop a substrate for their containerized street tree plantings from materials they had at their disposal, locally. I also get many questions from professional growers who are trying to develop substrates with specific properties.

    From today:
    Sent: Wednesday, December 29, 2010 17:36
    Subject: container gardening research in Philadelphia

    Dear Al,

    My name is Kristin Rhodes and I am a recent Architecture graduate from Philadelphia. I am currently working on an urban, contained garden project with International Design Clinic, a non-profit organization that seeks to provide creative solutions to social issues.

    I came across your research and expertise in container gardening and I would be most grateful for your time and any input in regard to our project in Philadelphia.

    The current project is located at a high school in center-city Philadelphia and the IDC is designing a canopy system from reclaimed chain-link fence that will control water run-off and channel water to contained gardens on the asphalt. The planters will undulate along with the canopy above it and will provide seating in some areas. The main goal in planting and creating a raised garden is to (1) slow down water, (2) absorb water and (3) purify/filter water.

    My primary point of research is in regards to the materiality of the planter. We will be constructing our own system, and we are interested in understanding the qualities of certain materials (wood vs. clay, vs. concrete, etc) and how that material will affect the water absorption/purification and plant growth.

    In your research on contained gardening you said that "soil is the foundation that all container planting is built on" - therefore, how much importance does the materiality of the container then bear on the success of water absorption and elimination of water run-off? If it does bear importance (perhaps in a more urban setting?) are you aware of specific data/research on container materials?

    I very much appreciate your time and expertise on this matter. Thank you very much.

    Kristin Rhodes
    International Design Clinic

  • grrrnthumb
    Original Author
    9 years ago
    last modified: 5 years ago

    Go get him Al! That is without a doubt plagiarism, since there is no permission you could give him that would allow him to incorrectly tell us it was his own work, and especially profit from saying that.

    In your clear-cup example, you are artificially forcing the water out of the peat by tamping. Stop there. Peat is unique in its ability to hold many times its weight in water and still hold air too. You've created a false situation by artificially squeezing the water out and testing quick before it has a chance to wick back away throughout the pot. It's ridiculous to liken that to a perched water table. Peat does not perch at the bottom of the pot like bark. Its capillary action, which bark doesn't have, wicks the water up and out, equalizing it throughout the pot. You would have to rush to do your little test before it wicks. So then without a parked "table", as in bark, there is no "perched water table", no point of "equilibrium" in the middle of the pot, no "gravity flow potential" to worry about.

    Regarding putting words in your mouth about your bark size, I'm just going by what you said. In your article at the link you gave me it says you use composted "bark fines", and the size you give for that is ""In geology, water can perch in clay strata above sand or gravel, but only if the particle size in the underlying substrate is larger than 2.1X the particle size up the overlying strata. The same holds true for "drainage layers" in containers."
    I'm sorry but no, the same does not hold true, because it would be ridiculous to try and equally apply such a rule to a wicking media (peat), and a non-wicking media (bark). Please state your source for such a specific claim ("2.1X") so that I can show you this research was meant for particles vastly different than potting media.

    "why is it that everyone that has tried the bark-based mixes refuses to return to peat/coir/compost-based soils"
    Really, everyone? I think yours is a fine mix Al, and I wouldn't pick on it unless you brought up these crazy absolutes, sooo, some quotes I dug up...

    "Aaaarghhh.. it seems whenever I've tried valiantly to give my container plants a fast-draining potting mix (using Al's recommends), they are wilting unless I water them sometimes even more than once a day, and this has been in only 70+ degree weather"
    -----
    "Other seedlings that were at the same growth stage that were not transplanted but in the original Pro Mix are growing and twice the size of the seedlings in the 5:1:1"
    -----
    "each affected plant (and African Violet) was started in a peat/perlite mix and was growing well but began to fail when moved to the either the gritty or the 5-1-1 mix; when removed, all had dead, brown roots"
    -----
    "They again failed; as with the prior ones, they stopped growing after 2-3 weeks, by week 4 the outer leaves were soft, but week 6 the whole plant was soft. When removed from the pot, the roots were dead with no sign of white"

    I know you'll say that's just anecdotal evidence, and they must have been doing something wrong, and I'll concede that. My point in showing them is that your anecdotal evidence is also worthless. You need real science. Not the pseudo-scientific mumbo-jumbo about capillary-equilibrium-gravitational-flow-potential that I've already shown you don't understand half of, but evidence based on real scientific experimentation as in the links I showed you.
    The way you become an "expert" is to do the empirical research & then report the numbers in a peer-reviewed publication. Second best is to compile other's real science & report on that. The third way, to report your personal interpretation of your own anecdotal experience, unfortunately does not make one an expert, only opinionated (like me!), and slightly less than forthright if we try to couch our opinions in science-speak to make them appear there is real science behind the numbers.
    I'm glad you included Kristin's letter, because she is asking for "specific data/research", just like me. So if you were to tell her "Water starts to perch in containers when the soil particles are something just a little larger than .1".", that is so numerically specific that it implies it has scientific experimentation backing it up, but doesn't; then you wouldn't really be communication honestly with her.

    Thank you for the offer of the gritty mix, but watering every day, when I have in the neighborhood of 150 pots, sounds like something I want to avoid. But thanks for the offer!

    - Tom

  • maltby
    9 years ago
    last modified: 5 years ago

    OK, so where is the best place to get pine bark fines around here to do Als mix?