Container soils and water in containers (long post)

March 19, 2005

The following is very long & will be too boring for some to wade through. Two years ago, some of my posts got people curious & they started to e-mail me about soil problems. The "Water Movement" article is an answer I gave in an e-mail. I saved it and adapted it for my bonsai club newsletter & it was subsequently picked up & used by a number of other clubs. I now give talks on container soils and the physics of water movement in containers to area clubs.

I think, as container gardeners, our first priority is to insure aeration for the life of the soil. Since aeration and drainage are inversely linked to soil particle size, it makes good sense to try to find a soil component with particles larger than peat and that will retain its structure for extended periods. Pine bark fits the bill nicely.

The following hits pretty hard against the futility of using a drainage layer in an attempt to improve drainage. It just doesn't work. All it does is reduce the soil available for root colonization. A wick will remove the saturated layer of soil. It works in reverse of the self-watering pots widely being discussed on this forum now. I have no experience with these growing containers, but understand the principle well.

There are potential problems with wick watering that can be alleviated with certain steps. Watch for yellowing leaves with these pots. If they begin to occur, you need to flush the soil well. It is the first sign of chloride damage.

One of the reasons I posted this is because of the number of soil questions I'm getting in my mail. It will be a convenient source for me to link to. I will soon be in the middle of repotting season & my time here will be reduced, unfortunately, for me. I really enjoy all the friends I've made on these forums. ;o)

Since there are many questions about soils appropriate for containers, I'll post by basic mix in case any would like to try it. It will follow the Water Movement info.

Water Movement in Soilssize>

Consider this if you will:

Soil need fill only a few needs in plant culture. Anchorage - A place for roots to extend, securing the plant and preventing it from toppling. Nutrient Sink - It must retain sufficient nutrients to sustain plant systems. Gas Exchange - It must be sufficiently porous to allow air to the root system. And finally, Water - It must retain water enough in liquid and/or vapor form to sustain plants between waterings. Most plants could be grown without soil as long as we can provide air, nutrients, and water, (witness hydroponics). Here, I will concentrate primarily on the movement of water in soil(s).

There are two forces that cause water movement through soil - one is gravity, the other capillary action. Gravity needs little explanation, but for this writing I would like to note: Gravitational flow potential (GFP) is greater for water at the top of the pot than it is for water at the bottom of the pot. I'll return to that later. Capillarity is a function of the natural forces of adhesion and cohesion. Adhesion is water's tendency to stick to solid objects like soil particles and the sides of the pot. Cohesion is the tendency for water to stick to itself. Cohesion is why we often find water in droplet form - because cohesion is at times stronger than adhesion, waters bond to itself can be stronger than the bond to the object it might be in contact with; in this condition it forms a drop. Capillary action is in evidence when we dip a paper towel in water. The water will soak into the towel and rise several inches above the surface of the water. It will not drain back into the source. It will stop rising when the GFP equals the capillary attraction of the fibers in the paper.

There is, in every pot, what is called a "perched water table" (PWT). This is water that occupies a layer of soil that is always saturated & will not drain at the bottom of the pot. It can evaporate or be used by the plant, but physical forces will not allow it to drain. It is there because the capillary pull of the soil at some point will equal the GFP; therefore, the water does not drain, it is "perched". If we fill five cylinders of varying heights and diameters with the same soil mix and provide each cylinder with a drainage hole, the PWT will be exactly the same height in each container. This is the area of the pot where roots seldom penetrate & where root problems begin due to a lack of aeration. From this we can draw the conclusion that: Tall growing containers are a superior choice over squat containers when using the same soil mix. The reason: The level of the PWT will be the same in each container, with the taller container providing more usable, air holding soil above the PWT. Physiology dictates that plants must be able to take in air at the roots in order to complete transpiration and photosynthesis.

A given volume of large soil particles have less overall surface area in comparison to the same volume of small particles and therefore less overall adhesive attraction to water. So, in soils with large particles, GFP more readily overcomes capillary attraction. They drain better. We all know this, but the reason, often unclear, is that the PWT is lower in coarse soils than in fine soils. The key to good drainage is size and uniformity of soil particles. Large particles mixed with small particles will not improve drainage because the smaller particles fit between the large, increasing surface area which increases the capillary attraction and thus the water holding potential. Water and air cannot occupy the same space at the same time. Contrary to what some hold to be true, sand does not improve drainage. Pumice (aka lava rock), or one of the hi-fired clay products like Turface are good additives which help promote drainage and porosity because of their irregular shape.

Now to the main point: When we use a coarse drainage layer under our soil, it does not improve drainage. It does conserve on the volume of soil required to fill a pot and it makes the pot lighter. When we employ this exercise in an attempt to improve drainage, what we are actually doing is moving the level of the PWT higher in the pot. This reduces available soil for roots to colonize, reduces total usable pot space, and limits potential for beneficial gas exchange. Containers with uniform soil particle size from top of container to bottom will yield better drainage and have a lower PWT than containers with drainage layers. The coarser the drainage layer, the more detrimental to drainage it is because water is more (for lack of a better scientific word) reluctant to make the downward transition because the capillary pull of the soil above the drainage layer is stronger than the GFP. The reason for this is there is far more surface area in the soil for water to be attracted to than there is in the drainage layer.

I know this goes against what most have thought to be true, but the principle is scientifically sound, and experiments have shown it as so. Many nurserymen are now employing the pot-in-pot or the pot-in-trench method of growing to capitalize on the science.

If you discover you need to increase drainage, insert a wick into the pot & allow it to extend from the PWT to several inches below the bottom of the pot. This will successfully eliminate the PWT & give your plants much more soil to grow in as well as allow more, much needed air to the roots.

Uniform size particles of fir, hemlock or pine bark 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 rapidly break down to a soup-like consistency. Bark also contains suberin, a lipid sometimes referred to as natureÂs preservative. Suberin is what slows the decomposition of bark-based soils. It contains highly varied hydrocarbon chains and the microorganisms that turn peat to soup have great difficulty cleaving these chains.

In simple terms: Plants that expire because of drainage problems either die of thirst because the roots have rotted and can no longer take up water, or they starve to death because they cannot obtain sufficient air at the root zone for the respiratory or photosynthetic processes.

To confirm the existence of the PWT and the effectiveness of using a wick to remove it, try this experiment: Fill a soft drink cup nearly full of garden soil. Add enough water to fill to the top, being sure all soil is saturated. Punch a drain hole in the bottom of the cup & allow to drain. When the drainage stops, insert a wick several inches up into the drain hole . Take note of how much additional water drains. This is water that occupied the PWT before being drained by the wick. A greatly simplified explanation of what occurs is: The wick "fools" the water into thinking the pot is deeper, so water begins to move downward seeking the "new" bottom of the pot, pulling the rest of the PWT along with it.

Having applied these principles in the culture of my containerized plants, both indoors and out, for many years, the methodology I have adopted has shown to be effective and of great benefit to them. I use many amendments when building my soils, but the basic building process starts with screened bark and perlite. Peat usually plays a very minor role in my container soils because it breaks down rapidly and when it does, it impedes drainage.

My Soilsize>

I'll give two recipes. I usually make big batches.

3 parts pine bark fines

1 part sphagnum peat (not reed or sedge peat)

1-2 parts perlite

garden lime

controlled release fertilizer

micro-nutrient powder (substitute: small amount of good, composted manure

Big batch:

3 cu ft pine bark fines (1 big bag)

5 gallons peat

5 gallons perlite

1 cup lime (you can add more to small portion if needed)

2 cups CRF

1/2 cup micro-nutrient powder or 1 gal composted manure

Small batch:

3 gallons pine bark

1/2 gallon peat

1/2 gallon perlite

handful lime (careful)

1/4 cup CRF

1 tsp micro-nutrient powder or a dash of manure ;o)

I have seen advice that some highly organic soils are productive for up to 5 years. I disagree. Even if you were to substitute fir bark for pine bark in this recipe (and this recipe will far outlast any peat based soil) you should only expect a maximum of three years life before a repot is in order. Usually perennials, including trees (they're perennials too, you know ;o)) should be repotted more frequently to insure vigor closer to genetic potential. If a soil is desired that will retain structure for long periods, we need to look to inorganic amendments. Some examples are crushed granite, pea stone, coarse sand (no smaller than BB size in containers, please), Haydite, lava rock, Turface or Schultz soil conditioner.

I hope this starts a good exchange of ideas & opinions so we all can learn.


Comments (158)

  • gardengal48 (PNW Z8/9)

    Sorry for coming into this a bit late - after the deluge of the last few weeks, we have just jumped head first into spring and I got real busy real fast!!

    Denise, acknowledging that your zone 8 climate is not the same as mine, I don't think that you should feel limited by what you can include in your new planters. Anything that grows in the ground here in my zone 8 can be expected to grow as easily in containers, given a few considerations. FWIW, most of my container gardens are year round, permanent plantings in that they winter over easily - the only exceptions may be some more semi-tropical items that will need winter protection.

    Plant selection should be wide open in zone 8. Because your summers are obviously a lot hotter than mine, you might consider plants that will tolerate a lot of heat. In fact I'd consider that to be more of limiting factor than worrying about their hardiness in winter. Container soils can heat up significantly in summer and if soil temps approach 90F, you will notice significant damage to your plants despite frequent watering. I'd look first to plants that are xeric in nature - these tend to be better adapted to the heat as well as droughts. Some items to consider would be plants with Mediterranean origins - rosemary, lavenders, thymes, lots of salvias, euphorbias, most anything with gray, fuzzy foliage. You could look at hebes for smaller evergreen shrubs, a number of dwarf conifers (pines, junipers, etc). Sedums, stonecrops and other succulents should do well also. And I wouldn't hesitate to use grasses - many will thrive in these conditions and a good many are evergreen as well (fescues, blue oat grass, New Zealand sedges, even NZ flax or phormiums). In fact a lot of plants originating from the southern hemisphere would be excellent choices - Australia, New Zealand, Tasmania. These more permanent plants, which I tend to choose for foliage and year round durability, can be supplemented with more seasonal color from tough annuals or more showy perennials - you can simply plant these in their containers within your larger container and change them out as they fade or the season progresses.

    Just re-read some of Al's previous comments and see he already mentioned the heat-root factor - great minds think alike :-)) I would also add that the larger the container, the less this becomes a serious issue, as there is more soil mass to insulate the roots.

    Hope this helps and gives you some ideas on what to include in your new planters.

  • PRO

    Breasley - probably, but give me some direction. Are you referring to plasmolysis (as in fertilizer burn), the effects of chlorides (ice melting compounds), chlorine in water, etc?


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  • breasley

    Al... in your original post in the 4th paragraph, you said "yellow leaves are the first indicators of chloride damage" referencing wick watering.

  • PRO

    As water is used by plants and as it evaporates, it leaves solutes (salts, specifically) in soils in increasing concentrations. Hi concentrations of soil salts can/will make water uptake by plants difficult or impossible. Water will not pass through cell membranes when the level of solutes in soil water is higher than in water bound within cell walls. In extreme cases, water is actually pulled from cells, even though roots might be awash in water. As water is pulled from cells, plasma is torn from cell walls and cells collapse, causing tissue death. This is termed "plasmolysis" and commonly called fertilizer burn, though it can also be caused by naturally occurring metal salts dissolved in the water you supply plants. It is much less likely to occur in well aerated soils that are watered from the top as water passing through the soil dissolves and washes accumulated solutes from the drain hole as it exits container.


  • maggie1


    Thank you so much for all the wonderful suggestions. As this project has progressed, I have started worrying that planters this size, and 7 of them, it would cost a lot of money to maintain. So the ideas of evergreen grasses, and small conifers and replace the blooming flowers only, will not only look good, but save me a small fortune.
    I love the tip to look for gray, fuzzy foliage. That's not the kind of thing they put on the tags at the nursery, and will be very helpful to steer me in the right direction.
    I do plan on painting the planters. Originally, I loved the idea of having a black door, and painting the planters to match. Not to worry though, after reading these posts, I will be painting them beige. I do have a lot of trees on my property, although this area is on the west side of my house, it should be the best of both worlds, some shade to cool off the area, but enough sun to get flowers to bloom. I hope.

    Thanks again for taking the time to give such a well thought out response. I have been going back and reading all the posts on this site. I have learned so much. Denise

  • breasley

    Thanks Al... I'm starting to see things your way!

  • nathanr

    Hi Al,
    You are such a great mentor to us I am going to reward you with more questions. These questions are mostly directed towards your Turface: turkey grit: pine bark (1:1:1) soil less tree mix that I plan to use for growing Ficus carica (edible fig) trees in large pots. 1) Im still not clear on the function of the turkey grit in this mix. Since the Turface is irregularly shaped and has lots of porosity and the grit has no pore space, why not just use 2/3 Turface and 1/3 pine bark and get the benefit of the greater surface area and lighter weight of Turface? 2) I have read a great number of your very insightful posts in various discussions and I still need clarification on the use of the terms pine bark, pine bark fines and composted pine bark. You mention that the composted bark is used in mixes for plants growing in it for 1 yr or less and uncomposted bark is used for longer term growth mixes. Do I understand correctly that bark fines are composted bark? 3) Is the pine bark (or fir bark) mentioned in your Turface, turkey grit, pine bark mix uncomposted? 4) Is there ever any toxicity problems when using uncomposted pine bark or has this only been attributed to cypress bark and cedar? 5) When using uncomposted bark you mentioned that it takes 2 times as much nitrogen to balance the nitrogen sequestered by microbial decomposition of part of the bark components. How much Osmocote (14/14/14) do you use per cu ft do you add to the mix containing uncomposted bark? 6) With the use of uncomposted pine bark, do you water with a fertilizer containing a higher proportion of nitrogen than is usually used in container gardening situations? 7) At what point in the life cycle of the soil do you no longer need to over compensate for the nitrogen? 8) What kind of wood do you use for making your grow boxes and do you treat it with anything? 9) How long do they usually last? 10) If I may ask, from what business in Chicago does your friend get you the fir bark? 11) Is there a practical way that I can measure total porosity and air porosity of potting mixes?

    Thanks so much for your help Al!


  • PRO

    Hi, Nathan. I saw this before I left for work & thought "No way can I answer this in a few minutes".

    The Turface is a great product for use in most soils, but few want to pay $8-9 for 50 lbs. One reason I use granite is, it's about half the price. The main reason is I like soils that require frequent watering. Soils that are watered daily or every other day, get a fresh charge of air each time you water - something that roots really appreciate. The granite provides about as much aeration and drainage as Turface, but holds insignificant amounts of water. I probably said that my basic soil for woody plants is 1:1:1 - bark:Turface:granite, but I regularly change that mix to suit individual plants. E.g., if I was potting an Acer, I would probably add an extra pint of Turface and a quart of bark to a gallon of that mix. For Juniperus, I would probably add a quart of granite to a gallon of mix. If you start adding larger quantities of Turface, you'll need to be sure fines are screened out. Even Turface that's too fine can turn Macro-pores to micro-pores, just like sand or compost.


    I use terms "pine fines" and "partially composted pine bark" (at top) interchangeably. Pine bark (at left) might look like what's in the photo. This is about as large a product as I use - a little finer is better if you can get it. Either product will work well in container soils, so long as you recognize that the fines will tend to hold more water and less air, and the uncomposted product will require more frequent fertilization. I do usually use an uncomposted bark, fir (at right in photo) or pine in woody plant soils. I prefer the partially composted bark in soils for herbaceous plantings & veggies, but again - either will work.

    I'm not trying to get anyone to grow in exactly what I use. I often say, "This is what I do" or "This is what has worked well for me." When I get specific questions like yours, others might get confused because I direct answers to an individual. I often point out disadvantages of using particular soils or components, but always expect that many will reject what I offer & continue about their business. I'm most interested in talking with those that are dissatisfied with their medium(s) or are already convinced that there is something better out there. ;o)

    I have never encountered what I even considered might be toxicity problems from plant metabolism by-products in conifer bark, but my growing experience has only included pine, fir, and hemlock. I was recently on a question/answer panel for a garden group. and one of the other participants revealed info from a just-completed study that indicated that those plants grown under cypress mulch fared poorly in trials. Because of probable phytotoxicity issues, I would not consider using it in soils (in fact, I'm finished with using it as a mulch as well).

    I'm guessing at using twice as much N in soils that have uncomposted bark vs. partially composted, but I'm close. I use a high N controlled release similar to Osmocote to get plants started, but don't rely on it. I think I am using a German brand of controlled release fertilizer I buy in 50 lb. bags. The formula is 19-5-8 with minors. While plants are active, I usually fertilize with a full strength solution of a balanced blend (20-20-20, e.g.) plus a full strength solution of 5-1-1 fish emulsion in the same water at same time. This varies by plant, but at least 75% of the woody stuff I'm growing get something like this. The flowery stuff gets a different program with more P. Can't answer the question about when soils stop needing extra N. Too many variables. You can get a rhythm in your fertilizer program by using the balanced blend as long as older leaves are nice & green. If you notice a lightening in older leaves, or a move to yellow, more N is required. After awhile, you'll know intuitively.


    Here are some grow boxes I use for small trees for bonsai. They're made from scraps & crating lumber we get various things in at my business. They're untreated & last about 5 years.

    I'll be seeing my friend at a bonsai meeting tomorrow night. I'll ask where he gets the fir bark & get back to you. On the bag, it says Vita-Bark - Fir bark for Orchids. It's packaged by Shasta Forest Products, Inc. in CA. Size is 1/8-1/4. I pay about 13.00 for 3 cu ft.

    To measure soil porosities - I left this as an answer to a question on another forum:
    "Your questions: Let's start with a dry media. It has two kinds of pores. It has the very tiny pores that are in the material itself. Some are microscopic and some are a little larger. We have to include the tiny spaces that are formed between soil particles in this category as well. These tiny pores are called micro-pores and hold water so tightly it is largely unaffected by gravity. Then, there are large pores, formed in the spaces between larger particles and particles that don't fit together well. These are macro-pores. The sum of these two types of pore space is the Total Porosity of the soil and it is measurable. Total soil porosity in container soils should never be less than 50% if plants are to grow to best potential - 75% is much better. If we wish to know the Air Porosity of the soil (how much air it holds), we can measure that as well. Air porosity in containers should be at least 25%, with 30 - 40% being better.

    To measure porosity: It can be done by weight or volume - I'll use volume here. A) Close/cover drain hole and measure the volume of the container - record. B) Dry enough soil to fill container, + a little extra in oven until completely dry. Fill container to rim & lightly tap on counter or ground to settle. Refill to rim with soil) C) Fill soil-filled container with water, being sure all particles are completely saturated. It might take an hour or more when soil is completely dry. Measure & record how much water it took. This measurement is total pore volume. You should see water glistening at the top of soil. D) Remove the drain hole cover & catch all water that drains. Measure & record.

    To calculate % of total porosity:
    Divide total pore volume by container volume & multiply by 100.

    To calculate total air porosity:
    Divide aeration porosity by container volume & multiply by 100.

    You can calculate the water holding porosity by subtracting aeration porosity from total porosity."

    Phew! I hope that answered most of the questions?

    Good growing.


  • nathanr

    Al; thanks thanks thanks! I'm sorry I made you repeat so much of what you have said in the past but I just needed some clarification on a few of these issues. Thanks for sharing the easy to understand soil porosity method.

    I can't wait to kick the peat habit and to try out some of your soil mixes and ideas. Well I just got my new pepper and tomato seeds in the mail and I better get my thermostats, heaters and fans checked out in my hot bed and all of this going for spring.

    Happy growing to you too.


  • PRO

    Nathan - For the fir bark:

    Oak Hill Gardens
    37W550 Binnie Rd
    West Dundee, IL 60118

    (847) 428-8500


  • nathanr

    Thanks Al.

    I live only about 45 minutes from Oak Hill Gardens and I will be giving them a visit soon. I'm curious to work with the legendary fir bark.

    Thanks again.


  • Mike Larkin

    Has anyone tried this product from ESPOMA
    I just got two bags thinking it was similat to Profile, but is was slighlty larger and gray gravel like.

    Al I mixed it with some Profile, Grit and small pine bark chips to make the conifer soil.
    The bag says it does retain moisture - not sure how much.

  • PRO

    Their (Espoma's) description could easily be describing Turface, so the products sound interchangeable. Espoma does up some beautiful packaging & puts fairly common stuff in them. Fired at 2000* is hot enough to insure it's a very stable product (won't turn to mush). I bet it's as good as or possibly better than Turface, and slightly larger is better in containers.


  • Mike Larkin

    It is larger in size that Turface -
    It is also cheaper - 27 lbs for 9.99
    The profile/turface is 40lbs for 29.99.

    I combinned the Espoma with the turface and the grit - then the mini pine bark. This should work well for the conifers-

  • PRO

    When I buy a pallet (40 bags), I get Turface delivered to my home or business for $7.97/ 50 lbs. By the 50 lb bag, it sells for about $8.50.

    I'm going to buy a bag of the Espoma stuff, just to see what it looks like. For others reading this and who might wish to make their own houseplant soil, the Espoma product Plantman is describing, like Turface, should be absolutely great in your soils, including those for cacti/succulents.


  • schusch

    Hello, Al-

    I have been busy trying to find the equivalent of chicken grit and Turface here in Europe, after the discussion of soil mixes in the maples forum - with, until now, limited results: the size of chicken grit here is smaller than BB size sand (about half), for instance, and is made of calcium carbonate. (Smaller poultry, I guess.)
    There are however a number of products that are used for soil improvement of golf courses, parks, etc. Do you have any thoughts about synthetic media? I found expanded polystyrene flakes (called Styromull) and ureaformaldehyde foams (Hygromull)- the former improves drainage, the latter holds water. They are used in pots, as well.

    Any thoughts about lava granules?

    Finally, I remember you saying that the sharp edges of chicken grit improves root ramification. In other words, that this is not harmful but beneficial. Can you elaborate?

    Thanks for all the generous info.

  • weebay

    I have tried to read all the info on this thread and others and have confused myself greatly.

    I know I shouldn't re use my old Pro Mix from last year. But may have to because of financial reasons. What can i add to it to make it more viable?

    Also I just throw the mix in the container and do not create a drainage layer. Do I really need a drainage layer? I have read that some just put a layer of styrofoam peanuts on the bottom. Will this help?

  • PRO

    Schusch - I'm sorry. I don't know how I could have missed your post. I thought the thread stagnant because it had "dropped down". It's likely that the soil improvers you can find will make good soil additives. Lava granules in 3-6 mm are very good. They will be more expensive than perlite, however. I'm not familiar the plastic foams, but as long as they are not phytotoxic, there is no reason they cannot be used as an amendment or component. I would decide based on the physical attributes.

    I grow some plants in all synthetic media - no organic component at all. I even use chemical nutrients on them with very good results.

    Fine rootage promotes finer branching - I do not know why, but bonsai practitioners are very aware of this reaction. Sharp and irregularly shaped soil particles promote root branching. First generation roots or the fine roots are the container work horses. They do all the important work and will even provide adequate anchorage for the relatively small plants we grow in pots. May I answer your question with a question? Does it make good sense to have your container full of fine, beautiful, useful, efficient rootage or with fat, ugly, lazy, useless roots. (I bet you hardly noticed how I tried to influence the answer). ;o) This is also why proper root pruning when repotting woody plants is key to vitality and longevity (another day).

    Weebay - If you find you need to reuse your mix from last year, it's not a crisis. I don't think it's best, but lots of people argue with me & think it's fine. If you can find some fine pine bark, you can mix it 50/50 with your old soil. Add an appropriate amount of perlite, and you should come up with a very usable soil.

    You do not need a drainage layer for good drainage. They do not promote drainage, only do they raise the level of saturated soil in containers. If you think your soil is holding more water than you wish, use a wick to drain the excess until your plant requires water at least every two days. Soils that remain saturated for too long kill roots and sap energy when roots rejuvenate. There is much mention of this throughout the thread.


  • schusch

    Thanks, Al-
    I remember you mentioning that irregular but also sharp edges encourage finer rooting. It made sense, then I read about roots on carniverous plants that sharp edges could hurt the roots. Which is why I asked.

    I recently discussed - via email - adequate soil mixes with two of the main maple growers here in Europe. When I told them I'd use bark piece sizes of 5-15mm (1/4 - 3/4 inch) they both encouraged even bigger sizes, one mentioning at least an inch. One of them mixes pine bark half with perlite and (unspecified) loam. Why the bigger size? When do the sizes get too big? I got the impression that they seem worried about keeping the mix cool in the summer, as much as good drainage.
    They also discouraged peat, as you have, in containers with bottoms. In Europe peat is still used a lot in commercial soil mixes - one needs to find ecologically sound gardening brands to find non peat mixes. I talked to a representative of one of the more serious 'alternative' soilmix business in Germany (by serious I mean that trying to get away from peat is only starting, and sometimes the material used encourages disease and other problems, if of inferior quality). He recommended a special mix they do that has composted bark, wood chaff, cocofiber and cocopeat. This seems typical for 'alternative' mixes. Do you have any experience with those? The person (himself a grower, not only an employee) also mentioned having to add more nitrogen, since cocofiber/peat fixes it more. Any thoughts?


  • PRO

    Larger soil particulates means larger soil pores which means superior aeration which means a very healthy rhizosphere which means sound rootage which means a vital plant is likely. Loam is a term that varies greatly from location to location To the Japanese, loam is volcanic rock that collects on volcano sides. It is often specified by color. I'm not sure what you call loam, here, it is equal parts of sand, silt, and clay - I consider it inappropriate in containers. I believe that in the UK, loam is compost or humus, so you can see it's difficult to judge its appropriateness in containers unless we know what we're talking about. Back to the particle size. Bigger is better, but bigger is also more work. As air porosity sneaks up past 40%, your soils will really require frequent watering - maybe twice or three times daily, depending on relationship between plant/container size. I grow in soils that are even more porous than I recommend here & try to build them so each plant requires water daily in the hottest part of summer.

    You mentioned temperature - an important consideration in all container culture. High temperatures (over 90 - 95* F. or 32 - 35* C.) inhibit root metabolism and extreme temps kill roots. Neither are good, and the latter sets up conditions for rot organisms to multiply later after temperatures return to an appropriate range. Shade containers when possible & grow in white or light containers when you can. Partially burying your containers is a good strategy too. Roots will run into soil and any PWT will be eliminated by the wicking action of the soil. Pot in pot growing also can be utilized to remove the PWT.

    I just don't like peat in volumes of more than 10-15% in containers for herbaceous material (flowers/foliage display plantings) and don't use it at all in my soils for woody plants. The plants just display much better vitality in the primarily bark mixes or in the case of woody plants, a mix of 1/3 bark & 2/3 inorganic parts. It's the added air in the bark mix. Sorry - I don't buy into the non-renewable resource peat thing.

    About this: He recommended a special mix they do that has composted bark, wood chaff, cocofiber and cocopeat.
    It's not as important to choose soil components, based on structural soundness, for plantings that are to last only a season as it is for plantings you'll have for two or more seasons between repots. I left this reply on the bonsai forum in answer to a question about using Coco shell mulch is a soil. It could easily have been offered as info on the soil(s) you're trying to develop:

    "Those that grow in containers generally do not depend on the media for nutrients; rather, they look to the nutrient supplementation program they have in place. If your soil is supplying substantial amounts of nutrients, it is being attacked structurally by microbial activity - it is breaking down. The organic portion of bonsai soil components are carefully chosen to retain structure for the intended life of the planting. Conifer bark is a widely chosen and readily available soil component. It retains its structure for several reasons: It is highly lignified - decay organisms break down cellulose much more quickly than lignin, making bark a much better choice than sapwood chips e.g. Conifer bark is rich in suberin, which is a lipid that helps bark resist decay organisms by making it very difficult for them to cleave hydrocarbon chains. Suberin is often referred to as "natures water-proofing for trees", and its presence in greater abundance in conifer bark is also why we generally prefer conifer bark to that of deciduous genera.

    To determine how valuable the CSM might be as a soil component, you might research the ratio of lignin:cellulose as compared to conifer bark. It almost certainly does not contain suberin in the amounts that conifer bark does. My guess is that it will not retain structure over the long term near as well as conifer bark."

    There are many things that affect the amount of N needed in soils. Plant material, porosity, watering frequency, in what state of decomposition the soil particulates are in, and the resistance of the soil parts to biotic activity can all play a part. Generally speaking, soils made with fresh bark and those made with organic parts that contain a higher percentage of cellulose and/or a lower percentage of lignin than conifer bark will require more N in the nutrient supplementation program.


  • schusch

    Thanks again for the elaborations. I need study your response more.

    I was indeed thinking about placing the 3 or 5 gallon pots in larger pots, both to shield them from the sun, as well as aesthetic reasons. I thought about filling in with pine bark. So you are saying if I place at least the lower part of the plastic pots in more soilmix that would help even if the holes are obstructed thereby. You are saying the water would exit anyway because of the wicking action of the surrounding soil? (May be I am asking a question that has been addressed elsewhere?)

  • PRO

    It is probably referred to above, but the practice is called "pot-in-pot" or sometimes "pot-in-trench" growing. If you think about it, the extra pot with soil, or the trench makes the water in your container "think" or react as though the container is actually deeper. In the case of the PIP, the water in the PWT moves from your container down to occupy the bottom of the extended container, leaving your soil drained. In the case of the trench or just partially burying the pot, the water in the PWT would be wicked from the soil in your container to dissipate into the earth. In order for this effect to work, the capillary pull of the lower soil plus gravitational pull must be more than the capillary pull of the soil in your container. It should work for all but those soils that hold water so tightly we should not be trying to grow in them.


  • nathanr

    Hey Al,

    1)You mentioned adding liquid kelp preparations as a micronutrient source to your potting mixes, how do you feel about incorporating kelp meal as a long acting source of micronutrients? I'm reluctant to buy the regular big bag of Peter's STEM micronutient product (25 lb)and can't seem to find a smaller size anywhere.
    2)Would it be useful to try to balance the increased need for nitrogen from the use of bark products by blending in feather meal? It is supposted to be a 4-5 month slow acting nitrogen source.

    By the way, I'm not an organic fanatic. I only care about what works.


  • nilaa

    Al, Is pine bark mulch different from fine pine bark? I wanted to make a small batch of soil according to ur soil recipe.


  • PRO

    Hi, Nathan. I have to admit to being unfamiliar with the Peter's product you mentioned. I'd like to read up on it, so if you have a link or can direct me to where I can find something on it ... I looked & couldn't turn up anything interesting after about 10 minutes. Sorry.

    I use fish and seaweed emulsions along with chemical fertilizers - I'm results oriented as well. I think that it's difficult to beat chemical fertilizers in containers for fast and effective results. I still use organic fertilizers, but they require biotic activity to break them down into elemental components the plant can use. The problem is: In containers, we cannot (maybe "should not" is a better phrase) depend on the boom/bust populations of micro-organisms being there when needed. Containers are generally much less hospitable to biota than mineral soils. Wide variance in temperature, moisture, and nutrient levels all impact soil organism populations. That said, I don't think I would depend on feather meal as a source of N in containers. Applications are easy, as is controlling concentrations with any one of a # of readily available fertilizer products.



    The product at the top is partially composted pine fines. It is sold as mulch, soil conditioner, pine fines, aged pine bark, and under other names. I just found some in Troy (near Detroit) for a person that contacted me through GW (she doesn't know it yet, though - I still have to write her to let her know). Lots of places will have it in the spring. Pine bark mulch can be any size, but the bark on the left is probably approaching the upper limit (size) of what most of you would like to grow in. Need more help?


  • katwomn59

    Lowes has big bags of soil conditioner and/or landscapers mix. The brand is "Scotchmans". It pretty much looks like the partially composted pine bark in Al's pic. I didnt buy it because it is in big bags and I dont have room to store it on my balcony (plus I have to carry everything up 3 flights of stairs!). So you might want to check it out. That is the closest thing I have seen to the composted pine bark.

    I potted all of my perrenial herbs in Al's mix last year. When I pulled one of them out of the pot recently, it had big strong roots all the way down to the bottom of the pot. I am sold on Als potting mix!


    BTW: A big "shout out" to Al! How ya doin? I havent been posting much but I check out this thread whenever it pops up. I made it through my first growing season and am about ready to start my spring planting!

  • PRO

    I have been noticing some of your posts lately & have been wondering how you are faring. I thought that you'd forgotten me. ;o) Thanks for the vote of confidence, Lydia. You've come far in a year. Good job! Good Luck!


  • nathanr

    Hello Al and everyone else too;

    Al you know we cannot forget you. You are the godfather of container gardening and potting mixes. Whenever I am working on my container projects, I often ask myself "what would Al think of this or that?" I still haven't actually grown anything is your potting mixtures since I was a latecomer (2006) to this thread and Spring has not yet sprung here in South Wisconsin. I fact, just yesterday I finally found a local source of Gran-I-Grit. I am very curious to hear from everyone (such as katwomn59)who has contributed to this thread as to what kind of triumphs and setbacks they have had in using Al's potting mixtures.

    Al, I made a false assumption on the Peter's Professonal S.T.E.M. (soluble trace element mix). I was on a citus container discussion thread http://forums.gardenweb.com/forums/load/citrus/msg071031588697.html
    and they were using the Scott's-Sierra (Peter's) S.T.E.M.
    which is available in 1 lb quantities from First Ray's Orchids. However, in comparing the 2 trace mixtures, the Micromax that you use has 6% Calcium and 3% Magnesium whereas the S.T.E.M. does not contain any. This is probably due to the inclusion of dolomitic lime (calcium and magnesium carbonate)in the Micromax which would contribute Ca and Mg in about a 2:1 ratio. They do have all of the other trace elements in common but in different ratios. The S.T.E.M. is a water soluble product whereas I presume the Micromax is not due to it containing the dolomite.

    This leads me full circle in my quest to find Miocromax in less than Al's industrial-sized packages. Has anyone found any souces of smaller bags of this product? Maybe this is an opportunity for some enterprizing person to start buying big bags of Micromax and to cut them down to 1 lb bags for sale to us little people.

    Thank you Al.


  • zzcooper


    I have found "hardwood fines" at a local Lowes. They also have pine bark chips that appear to look like the product on the right side of your photo. Which would be best for a large container where the media is changed yearly? Most of the ready made container soils have composted forest products, peat and perlite in them ....do you recommend adding more pine bark to the mix or does this only apply to made-from-scratch media?

  • girlndocs

    I found pine bark fines at Lowe's too, but the brand wasn't Scotchman's. I suspect the issue may be one of different "house brands" in different areas. Anyway, the fines I found here in Western WA were in a green-and-white bag, 2cuft for about $3, and displayed near the other bark mulches.


  • PRO

    Nathan - I don't want to have that kind of influence. ;o) Once you guys see the importance of air in container soils, you have the important stuff to build on. The rest of what I contribute is kind of unimportant individually, but might amount to something collectively. I've made some very special friends as a result of my time spent at GW, and I appreciate every one of them. Thanks for the nice comments.

    I was unaware that the STEM product was available. It sounds intriguing. I will ask grower friends about their possible knowledge of it and report if anything turns up. Because it is soluble and can be applied frequently in small doses, it has potential to be even more effective than MM nutrients. We'll have to see. I wonder how well it stores? 25 lbs is not too much for me, but it would be for most hobby growers. I have a wholesaler in GR, MI that lists it for just under $50/25 lbs.

    If you need a small qty of Micromax, I can put you onto a source - mail me.

    ZZ - I would tend to stay away from the hardwood mulch, no matter how appealing it looks. It breaks down quickly & loses it's structure. Heat build-up (composting) can be an issue too.

    Yes, you can usually improve a prepared/bagged soil by adding a good portion of pine bark to it. Those that reuse their soil from year to year would probably also benefit from excluding the compost, sand, and peat in favor of the bark as well.

    Kristen - You already know that I think you'll do very well & be pleased with your efforts. I admire your enthusiasm, it's catching and a tremendous asset that will only help you convince your plants that they should do their best growing for you. You remind me very much of Lydia, who has posted to this thread many times. ;o)

    Thread is winding down, but it's been great fun. A very dear friend pointed out how unusual it is to see a thread go so long and be free of any strife. You guys are great. All take care.


  • gardenlove

    Hello!...I am glad I ran across this thread because I am just getting prepared to put a soil mix of some kind into twenty large, deep plastic pots for outdoor container gardening(they are beautiful, Italian made relief patterned Faux Terra Cotta that I picked up very reasonably a couple years ago) I have a large amount of something called "Organic Compost" made by Soilprep at www. soilprep.com I bought it at my local Dollar treee Store for a buck a bag!(.5 Cubic Foot)...its made of "A medium/coarsely textured compost, rich in humus, and derived from various woods and forest products". I guess I am supposed to mix it 50/50 with regular topsoil, but my local soil is full of rocks and weeds and weed seeds. I am wondering how I can use this particular product in a potting mixture that will support the growth of many various types of flowers and plants? I want to grow annuals and perennials(some from seed, maybe a couple of container roses, some veggies and herbs, etc. Can I mix it with regular bagged potting soil instead of my rocky, weedy topsoil?(at what ratio?..and what else would I need to add?) I also found Blue Ribbon D.E. premium Cat Litter(made only of Diatomaceous Earth)..it says on the bag it can also be used as a "Soil Conditioner-mix with garden and potting soils to increase moisture retention".....would this be good or bad to add to my Compost/potting soil mix? I have Osmocote and can get lime if neccessary to improve my mixture. Any thoughts would be appreciated before I get started filling my TWENTY pots!....cost is an issue and because I have so many to fill, I am trying to do it smart, but without breaking the bank..thanks for any advise!...GardenLove

  • PRO

    Hi GL - I went to the website & couldn't find out much about what your bagged material is made from. I suspect it is a mix of a wide variety of wood products that includes leaves, bark, and sapwood that has composted for a year or so. If you need to use this for economic reasons, there are probably ways to work with it to give you a soil you might be happy with. Is there a way you can send a photo of a handful of the mulch so I can get an idea of the texture - maybe even the content of it? I always mention that any sapwood and non-conifer tree bark is going to make some nutrient and possibly some structure problems over the course of a grow season, but I might be wrong.

    You won't need the DE. It's much too fine for any soil use other than as a surface applied mechanically acting insecticide. Best to leave the garden/topsoil out of the mix, too. I'm thinking you might need some pine bark, some sphagnum peat, and some perlite (all pretty inexpensive components) to build a soil. You can e-mail me if you wish (if you've forgiven my errant e-mail). ;o) Or we can do it here.

    The description of your home on your member page is impressive - sounds beautiful. Others might want to have a read. Good luck.


  • nilaa

    Al, I wasn't able to find pine bark similar to the one u have showed in the photo, the pine bark mini nuggets looked like the left one in ur picture, so what else can i use? can i buy these and use it for next yr? I will look out for it in other nurseries and garden centers.

  • southernheart

    Hi Al, and everyone here...

    I'm fairly new to this forum and am enjoying learning more in preparation for this spring and summer.

    I plan on making a big batch of your soil mix this month (my son is a Turf Grass Agronomy major, so Turface should be easy to come by :). I wondered if there is anything in particular I should do to help with moisture-retention? I am in Memphis (z7), and the main problem I have in the summer is frequent/quick drying-out of my containers.

    Thanks so much for sharing your expertise!


  • anney


    Put water gels in your planting mix if you want to water less often, and try the soiless mix recipes that have been posted in this thread. Just google "plant water gels" and you'll see many descriptions and brand names of them.

  • katwomn59

    No Al of course I haven't forgotten about you! For various reasons, I have been spending less time on the internet. I still check out the various threads. But after getting through my first growing season, I am more relaxed. I have learned a lot and I dont freak out over every little thing and send panicy emails or posts like I used to LOL! I remember you telling me not to stress so much and gardening is pretty much trial and error. And I have seen for myself that you were right!

    It is finally last frost in my zone, and I am poised to start my spring planting. This year I am planting all my perennial herbs in cocopeat and coconut husk chips (CHC). Everthing did really well in the pine bark mix but as I mentioned before, I had a hard time getting the pine bark in manageable quanities. Plus most of my herbs like dry conditions so I had a problem with the rewetting issue. So I have switched to CHC (but still using your recipe!). Everything was growing just fine, but I got a spider mite infestation and trashed most of my plants towards the end of summer. I replaced the thyme and sage and potted them in the CHC and cocopeat. And they seem to be doing great. It is more expensive and not easy to find in some places, but I got the cocopeat at a hydroponics store (and was actually cheaper than regualar peat). The CHC I got from a local orchid supplier. I think it will work well for me in this hot climate. The CHC drains really well and stays pretty loose. There is no problem with rewetting and it is supposed to hold up even longer than pine bark.

    It may not be practical in large quantities. It is not cheap and probably not readily available everywhere. But for people who dont need large quantities, have a tendency to overwater (like me!) and are growing perrenials that need both dry conditions and good drainage and aeration, I think it is worth trying. The biggest hassle is the washing and rinsing necessary to get rid of the salt.

    I know you are able to get pine bark, etc in cheaply and in bulk, and you know it's properties, but if you ever decide to experiment with CHC and cocopeat, I would love to see what you think!


  • PRO

    Wow - I see this thread has shifted to high gear. The soil I make is not a guarantee that all will go perfectly. It is just a blend that has shown to reliable retain its structure for a full growing season and in most cases two. The other soils I mention incidentally that contain the Turface, Haydite, pumice, crushed granite, etc., are soils I use for woody things that may go extended times between repotting. In every case, it is the soil aeration and drainage that are my first consideration. There are too many physiological issues to contend with (root-rot aside) for me to consider growing in a mix that doesn't drain or hold air. THAT is the most important thing anyone can take from this looong thread. Lack of air in the roots is most often responsible for things even as seemingly removed as insect infestation and fungal attack - lowered defenses (energy) due to compromised vitality.

    It's not necessary to use the mix I do to have good vitality in plants. I always hope you will find a way to try the soils I use because it they make your job easier and minimize mistakes, but all are not willing to go through so much trouble to find the ingredients. Keep your eyes peeled for the bark, it's worth looking for and using, but don't worry so much if you can't find it.

    There are lots of good tips upthread from others, too. I like to water frequently, so I have no use for the polymer crystals, but I know they work to extend watering intervals - that from Anney and others (I'm sure you saw that, Andrea? Welcome to the forum, too btw). Lydia is a year into her gardening adventure and looking for ways to improve on what she was using, tailoring soil(s) for specific needs. Cheers on you, Lydia - and I will try the chc's on some plants this year.

    Good growing.


  • southernheart

    Thanks so much to both anney and Al for the advice...I will definitely use those, also!


  • nathanr

    Hi all,
    For those who may doubt Al's wisdom, on drainage, aeration and PWTs (you haven't forgotten PWTs from last year already have you?), I performed an experiment and was amazed by what I saw. I filled a large styrofoam cup with 1000 mL (about 1 quart)of Turface MVP which ends up being 6.25 inches deep in the cup. I saturated the Turface to it's top with water and allowed it to sit a day and then added more water to top it off again. I then poked several small holes in the bottom of the cup and allowed the water to run out until no more came out of the holes. This only took about 15 minutes since Turface is very fast draining. At this point 265 ml of water ran from the holes in the cup. I then used a pair of very pointed forceps to shove a rayon wick up into the Turface through the bottom of the cup and immediately a small stream of water ran down the wick and an additional 80 mL drained from the wick. Most of this within the first hour afterwards. This shows that Turface MVP has an air space of about 35% just as the manufacturer claims. The interesting thing though is that I calculate that the added 80 mL of water if left standing in the pot would leave the bottom 1.8 inches of the potting medium totally saturated. Most roots could not grow or survive long in this saturated zone as it would be a very unhealthy low-oxygen place for them. Turface is a highly porous and fast-draining medium. Although I haven't tried it yet I'm sure that the same experiment performed with a peat based potting media would have much worse results. With the PWT and the saturation zone being much higher in a pot filled with this much finer medium. This may just be a re-hash of what many of you already know but it is fascinating to see the physics of it operating right before your eyes.

    Good luck everyone.


  • southernheart

    Al and Nathan, I hope that you don't mind my sharing a humorous story about Turface, that really highlights your points and underscores how respected a product Turface is in the industry.

    My son is a Turf Grass Agronomy major at a large Southern university, and did an internship last spring/summer at one of the major league baseball spring training facilities in Florida. Turface is used for excess water on the fields that occurs during rainstorms, especially those "popcorn" showers (downpours) that occur frequently in Florida. It has helped prevent many a game "rainout" due to its effectiveness. It takes many bags of Turface to do this (for one game), which can become a bit pricey---so it's a protected commodity in the baseball industry.

    During one sudden torrential downpour, the Grounds Crew quickly pulled the tarp over the infield, and then took cover in the visiting team's dugout to wait out the storm. The Turface bags were kept to the side in the visiting dugout, near where the Grounds workers were standing. The visiting team's pitcher had a bad inning just prior to the rainstorm, and came into the dugout kicking and throwing things, as they sometimes do. As he looked for things to use to vent his frustration, he eyed the bags of Turface to the side, and the Grounds workers caught his glance, and could tell that he was tempted to kick them, also. They immediately, in *unison*, said "don't even think about it!". Throw your glove, knock over some bats, kick the bubblegum containers over, but don't mess with the Turface...unless you want to take on the Grounds Crew... :)

  • esthomizzy

    What a fantastic thread. Iowa Jade from the Rose forum drew my attention to it.

    I'm about to pot up a huge container and will attempt to follow the advice. Some questions if I may.

    I am generally happy to water every day but for times of going on holiday etc and having to leave my poor plants in the care of an uncaring non gardener I will also be continuing the use of water retaining gel crystals unless anyone thinks that's a definite no no. Having just done a recce of the local homebase (I guess that's like the UK version of Home Depot). I think the mini bark chips they have are about 1/2" is that ok size wise? I have some vermiculite in the back of a cupboard at home which has been sitting there for years would it be possible to use some of that along with perlite (as a part perlite replacement) to use it up or would that be a bad idea? I couldn't find any plain peat at my store would all purpose compost be ok or would that be very bad? I have previously believed (and I'm not certain entirely where my beliefs came from) that using a part compost/peat based product combined with a loam based product and manure was a good idea. Some stuff planted that way (thirds of each) seems to be just fine but I'm always on the lookout for improvements.

    I can't wait to try the wicking. I've never been particularly comfortable with the idea of drainage matter at the bottom of pots. As I grow space hungry clematis as well as roses I've always thought they would probably prefer more soil to grow in.

    Thanks for all the input everyone. It has been very illuminating.

  • jonathancox007_yahoo_com_nz

    Hi Al,a lot of interesting information here.
    I have been trying to grow dwarf citrus for ages and keep on
    drowning them in variuos potting mixes.They tend to drop their
    leaves and twig die back and then snuff it.I live in Auckland
    new Zealand and we get a lot of rain through winter.I have
    tried chc/peat at 4 to 1.I have tried chc/coir and 4 to 1
    and they have still remained too damp.I know now as well as
    staying too wet they are not getting enough air in their
    roots. I was thinking of doing one of two things
    1.potting in pure 1/2 inch chc chips in a tallish pot,i am
    concerned about shock from transplanting from a tight medium
    from the contaner mix.
    2.Transplanting into a coarse free draining orchid mix.
    It doenst go over 26 c here in summer and the mix must drain well.Any advice would be much appreciated,cheers

  • Teddy p

    Thank you so much, Al! and everyone! Although I have container gardened for years, you all really taught me A Lot!!!! Many thanks, T

    tapla thanked Teddy p
  • PRO

    You're welcome, Teddy. You stumbled on an old thread that was originally posted when Garden Web only allowed 150 posts to any thread before they closed it to further posting. Click this link to go to the most recent post(s).


  • bragu_DSM 5

    bump, because y'all should know al didn't always write long ^_^

    besides, this post made it 'clik' for me, oh so long ago

  • PRO

    It was fun to scroll through what I think was the first posting of the Water Movement thread. Hard to believe it will be 12 years old in a few days.

    Time flies like an arrow. Fruit flies like a banana.

    CLICK ME to go to the most recent (active) thread.


  • Cherry Geathers



    sorry FOR THE CPAS/

  • Cherry Geathers

    About modifying the drainage holes so the dirt doesn't wash out. I have been using the mesh that is put in window screens. It is sooo cheap and a couple of yards might supply you with hundreds of patches for your pots.

  • Cherry Geathers

    Me again. A wonderful use for wicks is to use them as a watering source rather than a drainage source with a couple of caveats. I use synthetic yarn so the wicks don't rot. Using soiless media with extra perlite for aeration is needed because the soil is constantly damp and this helps avoid root rot. For my use I find that it's effective for pots up to six inches tho' my sister suggested using a double wick which I didn't try. It is super for seedlings and once that capillary actions starts, you basically don't have to water at all. (An African violet trick). You pot the plant with the wick wound around the bottom of the pot and allow the yarn to dangle as far as your water source is deep.(. I used to have it threaded half way into the pot but it doesn't woKl any better)

    Sit the pot in water until the wick is soaked. Then suspend the pot over any water source with the wick dangling . Since I grow plants by the hundred, I use those plastic grids that are made for florescent light fixtures, Lately I am trying closet maid wire shelves because they are more sturdy than the plastic. To holdt he water , I use shallow plastic storage boxes that I try match to the size of the shelves. You can use soluble fertilizer in whatever you use to hold the water supply.

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