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CONTAINER SOILS - WATER MOVEMENT and RETENTION XXII

tapla
February 15, 2015
last modified: February 15, 2015

Hello! Houzz's new format has presented some challenges, but it
looks like there has been some changes that will allow me to repost the thread
in its entirety. Hopefully you'll view that as a GOOD thing. I need to
thank all the growers and good people who have been so supportive of the thread
over the years. Their contributions are one of the main reasons viewers
continue to find interest in it, so thank you very much! If you find value
in the information I have set down in this post and feel there is anything
pertaining to the topic that should be added or explored in more detail, please
contribute your suggestions. My goal was to offer soil-related information with
the potential to help you increase the reward you get in return for your
efforts. What might I do to increase the value of this offering?

As you eye the length of this post, one thing you might ask
yourself is, "Why the interest and all this talk about soils and water
retention?" In all honesty, soils obscure the reason we talk about them -
they hide the roots and the roots' state of vitality. Vitality is not the same
as vigor. Vigor is a genetic factor, something the plant is endowed with because
of how it was programmed by Mother Nature.
It is also something we have no sway over. Vitality, on the other hand,
is dynamic and variable, essentially a measure of how well a plant is/ has been
able to deal with the cultural hand it has been dealt. Vitality is something
you have much control over. It is the visual signals we get from the parts of
the plant we CAN see that allow us to take measure of the condition of the
roots, their vitality. Soil choice, combined with watering habits, have a very
significant impact on root health. As you read, keep in mind that good root
health and root function is an essential PREREQUISITE to a healthy plant.
You cannot expect to grow healthy plants w/o a healthy root system - it is
impossible; which brings us full circle to why we discuss soils.

Poor root health is responsible for a very high percentage of the
ills that befall plants, and the reasons people flock to the forums seeking
help for widely varying issues. Poor root health means a reduction in vitality,
which leaves the plant looking shabby while compromising its ability to defend
itself against insects and diseases.

So let us talk about some things we can implement that should go a
very long way toward providing you with the ability to consistently keep the
root systems of your plants happy.

I started this
thread about 10 years ago, in March of '05. So far, it has reached the maximum
number of posts GW allows to a single thread twenty times, which is much more
attention than I ever imagined it would garner. I have reposted it in no small
part because it has been great fun, and a wonderful catalyst in the forging of
new friendships and in increasing my list of acquaintances with similar growing
interests. The forum and email exchanges that stem so often from the subject
are in themselves enough to make me hope the subject continues to pique
interest, and the exchanges provide helpful information. Most of the motivation
for posting this thread another time comes from the reinforcement of hundreds
of participants over the years that strongly suggests the information provided
in good-spirited collective exchange has made a significant difference in the
quality of their growing experience. I'll provide links to some of the more
recent of the previous dozen threads and more than 3,000 posts at the end of
what I have written - just in case you have interest in reviewing them. Thank
you for taking the time to examine this topic - I hope that any/all who read it
take at least something interesting and helpful from it. I know it's long, and
grows a little longer each time it's reposted. My hope is that you find it
worth the read, and the time you invest results in a significantly improved
growing experience. Since there are many questions about soils appropriate for
use in containers, I'll post basic mix recipes later, in case any would like to
try the soil. It will follow the information.

Before we get started, I'd like to mention that I wrote a reply
and posted it to a thread some time ago, and I think it is well worth
considering. It not only sets a minimum standard for what constitutes a 'GOOD'
soil, but also points to the fact that not all growers look at container soils
from the same perspective, which is why growers so often disagree on what makes
a 'good' soil. I hope you find it thought provoking:

IS SOIL 'X' A GOOD SOIL?

I think any discussion on this topic must largely center around
the word "GOOD", and we can broaden the term 'good' so it also
includes 'quality' or 'suitable', as in "Is soil X a quality or suitable
soil?"

How do we determine if soil A or soil B is a good soil? and before we do
that, we'd better decide if we are going to look at it from the plant's
perspective or from the grower's perspective, because often there is a
considerable amount of conflict to be found in the overlap - so much so that
one can often be mutually exclusive of the other.

We can imagine that grower A might not be happy or satisfied
unless knows he is squeezing every bit of potential from his plants, and grower
Z might not be happy or content unless he can water his plants before leaving
on a 2-week jaunt, and still have a weeks worth of not having to water when he
returns. Everyone else is somewhere between A and Z; with B, D, F, H, J, L, N,
P, R, T, V, X, and Y either unaware of how much difference soil choice can
make, or they understand but don't care.

I said all that to illustrate the large measure of futility in
trying to establish any sort of standard as to what makes a good soil from the
individual grower's perspective; but let's change our focus from the pointless
to the possible.

We're only interested in the comparative degrees of 'good' and
'better' here. It would be presumptive to label any soil "best".
'Best I've found' or 'best I've used' CAN sometimes be useful for comparative
purposes, but that's a very subjective judgment. Let's tackle 'good', then move
on to 'better', and finally see what we can do about qualifying these
descriptors so they can apply to all growers.

I would like to think that everyone would prefer to use a soil that can
be described as 'good' from the plant's perspective. How do we determine what a
plant wants? Surprisingly, we can use %s established by truly scientific
studies that are widely accepted in the greenhouse and nursery trades to
determine if a soil is good or not good - from the plant's perspective, that
is. Rather than use confusing numbers that mean nothing to the hobby grower, I
can suggest that our standard for a good soil should be, at a minimum, that you
can water that soil properly. That means, that at any time during the growth
cycle, you can water your plantings to beyond the point of saturation (so
excess water is draining from the pot) without the fear of root rot or
compromised root function or metabolism due to (take your pick) too much water
or too little air in the root zone.

I think it's very reasonable to withhold the comparative basic
descriptor, 'GOOD', from soils that can't be watered properly without
compromising root function, or worse, suffering one of the fungaluglies that
cause root rot. I also think anyone wishing to make the case from the plant's
perspective that a soil that can't be watered to beyond saturation w/o
compromising root health can be called 'good', is fighting on the UP side logic
hill.

So I contend that 'GOOD' SOILS ARE SOILS WE CAN WATER CORRECTLY;
THAT IS, WE CAN FLUSH THE SOIL WHEN WE WATER WITHOUT CONCERN FOR COMPROMISING
ROOT HEALTH/ FUNCTION/ METABOLISM. If you ask yourself, "Can I water
correctly if I use this soil?" and the answer is 'NO' .... it's not a good
soil .... for the reasons stated above.

Can you water correctly using most of the bagged soils readily
available? 'NO', I don't think I need to point to a conclusion.

What about 'BETTER'? Can we determine what might make a better
soil? Yes, we can. If we start with a soil that meets the minimum standard of
'good', and improve either the physical and/or chemical properties of that soil,
or make it last longer, then we have 'better'. Even if we cannot agree on how
low we wish to set the bar for what constitutes 'good', we should be able to
agree that any soil that reduces excess water retention, increases aeration,
ensures increased potential for optimal root health, and lasts longer than
soils that only meet some one's individual and arbitrary standard of 'good', is
a 'better' soil.

All the plants we grow, unless grown from seed, have the genetic
potential to be beautiful specimens. It's easy to say, and easy to see the
absolute truth in the idea that if you give a plant everything it wants it will
flourish and grow; after all, plants are programmed to grow just that way. Our
growing skills are defined by our ability to give plants what they want. The
better we are at it, the better our plants will grow. But we all know it's not
that easy. Lifetimes are spent in careful study, trying to determine just
exactly what it is that plants want and need to make them grow best.

Since this is a soil discussion, let's see what the plant wants from its
soil. The plant wants a soil in which we have endeavored to provide in
available form, all the essential nutrients, in the ratio in at which the plant
uses them, and at a concentration high enough to prevent deficiencies yet low
enough to make it easy to take up water (and the nutrients dissolved in the
water). First and foremost, though, the plant wants a container soil that is
evenly damp, never wet or soggy. Giving a plant what it wants, to flourish and
grow, doesn't include a soil that is half saturated for a week before aeration
returns to the entire soil mass, even if you only water in small sips. Plants
might do 'ok' in some soils, but to actually flourish, like they are
genetically programmed to do, they would need to be unencumbered by wet, soggy
soils.

What defines our proficiency as growers is our ability to identify
and reduce the effects of limiting factors, or by eliminating those limiting
factors entirely; in other words, by clearing out those influences that stand
in the way of the plant reaching its genetic potential. Even if we are able to
make every other factor that influences plant growth/ vitality absolutely
perfect, it could not make up for a substandard soil. For a plant to grow to
its genetic potential, every factor has to be perfect, including the soil. Of
course, we'll never manage to get to that point, but the good news is that as
we get closer and closer, our plants get better and better; and hopefully,
we'll get more from our growing experience.

In my travels, I've discovered it almost always ends up being that
one little factor that we willingly or unwittingly overlooked that limits us in
our abilities, and our plants in their potential. MOTHER NATURE ALWAYS SIDES WITH
THE HIDDEN FLAW.

Food for thought:

'A 2-bit plant in a $10 soil has a future full of potential, where
a $10 plant in a 2-bit soil has only a future filled with limitations.' ~
Al

CONTAINER SOILS - WATER MOVEMENT and RETENTION

As container gardeners, our first priority should be to ensure the
soils we use are adequately aerated for the life of the planting, or in the
case of perennial material (trees, shrubs, garden perennials), from repot to
repot. Soil aeration/drainage is the most important consideration in any
container planting. Soils are the foundation that all container plantings are
built on, and aeration is the very cornerstone of that foundation. Since
aeration and drainage are inversely linked to soil particle size, it makes good
sense to try to find and use soils or primary components with particles larger
than peat/compost/coir. Durability and stability of soil components so they
contribute to the retention of soil structure for extended periods is also
extremely important. Pine and some other types of conifer bark fit the bill
nicely, but I'll talk more about various components later.

What I will write also hits pretty hard against the futility in using a
drainage layer of coarse materials in attempt to improve drainage. It just
doesn't work. All it does is reduce the total volume of soil available for root
colonization. A wick can be employed to remove water from the saturated layer
of soil at the container bottom, but a drainage layer is not effective. A wick
can be made to work in reverse of the self-watering pots widely being discussed
on this forum now.

CONSIDER THIS IF YOU WILL:

Container soils are all about structure, and particle size plays
the primary role in determining whether a soil is suited or unsuited to the
application. Soil fills only a few needs in container culture. Among them are:
Anchorage - a place for roots to extend, securing the plant and preventing it
from toppling. Nutrient Retention - it must retain a nutrient supply in
available form sufficient to sustain plant systems. Gas Exchange - it must be
amply porous to allow air to move through the root system and gasses that are
the by-product of decomposition to escape. Water - it must retain water enough
in liquid and/or vapor form to sustain plants between waterings. Air - it must
contain a volume of air sufficient to ensure that root
function/metabolism/growth is not impaired. This is extremely important and the
primary reason that heavy, water-retentive soils are so limiting in their affect.
Most plants can be grown without soil as long as we can provide air, nutrients,
and water, (witness hydroponics). Here, I will concentrate primarily on the
movement and retention of water in container soil(s).

There are two forces that cause water to move 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 container than it is for water at the
bottom. 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; in other words, water's bond to
itself can be stronger than the bond to the object it might be in contact with;
cohesion is what makes water form drops. 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, and it will stop rising when the GFP equals the capillary attraction of
the fibers in the paper.

There will be a naturally occurring "perched water
table" (PWT) in containers when soil particulate size is under about .100
(just under 1/8) inch. Perched water is water that occupies a layer of soil at
the bottom of containers or above coarse drainage layers that tends to remain
saturated & will not drain from the portion of the pot it occupies. 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
surpass the GFP; therefore, the water does not drain, it is said to be
'perched'. The smaller the size of the particles in a soil, the greater the
height of the PWT. Perched water can be tightly held in heavy (comprised of
small particles) soils where it perches (think of a bird on a perch) just above
the container bottom where it will not drain; or, it can perch in a layer of
heavy soil on top of a coarse drainage layer, where it will not drain.

Imagine that we have five cylinders of varying heights, shapes, and
diameters, each with drain holes. If we fill them all with the same soil mix,
then saturate the soil, the PWT will be exactly the same height in each container.
This saturated area of the container is where roots initially seldom penetrate
& where root problems frequently begin due to a lack of aeration and the
production of noxious gasses. Water and nutrient uptake are also compromised by
lack of air in the root zone. Keeping in mind the fact that the PWT height is
dependent on soil particle size and has nothing to do with height or shape of
the container, we can draw the conclusion that: If using a soil that supports
perched water, tall growing containers will always have a higher percentage of
unsaturated soil than 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. From
this, we could make a good case that taller containers are easier to grow in.


Continued below

Comments (987)

  • tropicofcancer (6b SW-PA)

    Mblan: I wrote in another post on air layering and hopefully that may be useful for you also. I have done it on regular green JM (I think this is generally used for rootstock) and coral bark maple. I have consistently failed on "Nishiki Gawa" that I have in ground. Seems like some cultivars may be tougher to root via air layer. This year I am leaving two of the 1 yr rooted cuttings in their pots buried in soil with lots of leaves. I am hoping they will survive and be healthy in spring.

    Does the 45F side of garage stay at 45F the whole winter? I doubt it. If there is a common wall, I would pick the colder side and build a simple sheltered structure against the warm-side wall. Probably a styrofoam box or something like that.

  • mblan13

    It kinda does. The lowest it goes is 42-43 because the furnace is there. Once it gets down to that temperature it pretty much stays there. The door stays shut and one wall faces North, the other Faces East, with a garage that shades it from the morning sun. There is living space above, so no roof to warm it up. Average temps, not just daytime highs, have to go significantly above that 45 for several days for the temp in the garage to rise. Even then it will creep slowly up. It kind of works as a natural cooler.

    I was going to prune said branches in the spring for styling, so it's no loss if they don't root. I figured instead of pruning and trashing, I could make 2 more trees and get some experience with air layering.

    Thanks for the link on the air layering. I'm starting to feel a bit like a mad scientist with all this. Whooda thunk there was so much control over how, when, why and where a tree grows! I guess thats what people did before TV was invented.

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  • westes Zone 9a California SF Bay

    I understand why we filter turface and fir bark in the gritty mix, with particular emphasis on removing out the fines. But - after the fines are removed - is there any reason why the grit/gravel/stone part of the mixture cannot contain larger stones? If I wanted to use a mixed gravel that had pieces between 1/8th and 3/4 inches - instead of a gravel that is filtered 1/8th to 3/8th inches - how will that affect the gritty mix? I am assuming that you use an equal volume of each type of stone.

    Just for full disclosure, I mix my gritty mix to be a little more water retentive as:

    * 4 parts turface (fines removed)

    * 3 parts fir bark (fines removed) up to 3/8th inch

    * 2 to 3 parts stone that is 1/8th to 3/8th inch (I alter the amount of stone mainly for aesthetic reasons)

    I want to understand how using the larger 1/8th to 3/4 inch mixed size gravel would alter the characteristics of gritty mix.

  • halocline

    westes - It would effect how the water moves through the soil by disrupting it's anticipated adhesion, and cohesion properties. Larger stones would create variable sized spaces between soil particles, resulting in lower water retention in areas with larger voids; due to the lack of water adhesion. These same large gaps could also become filled with smaller soil particles; creating increased water retention, and possible soil compaction. Uniformity is key to achieving proper "WATER MOVEMENT and RETENTION".

    Additionally, the "Grit" portion of the soil mix serves as more than just a filler. Depending on what you're using, it play's a part in controlling water retention, as most materials used, hold very little to no moisture (or nutrients). A lot of people use "Chicken Grit" (Insoluble Crushed Granite); which has particularly sharp edges, so when the root's grow into them; they split, rather than simply growing around the obstruction, thus creating a denser root mass.

    If you prefer a more visually pleasing soil appearance, you can use almost any material you like, as simply a "Top Dressing".


    Rob

  • halocline

    How your soil aggregate materials are reduced to the convenient screenable sizes you buy as a consumer.

    https://www.youtube.com/watch?v=1CpjRMICXNM


    (Center Spine Bud Imprint on Agave colorata under L.E.D.)


    Rob

  • teener629

    I've spent the last few hours making notes from this page and others here after purchasing my first major :) house plants (FLFs). It's wonderful, thank you! I started thinking somebody here should make and sell some of this 5:1:1 soil on etsy since the components seem to be hard to find for some people! I did find some bark there, has anybody seen or tried buying this instead of sifting themselves? Would reptibark be just as good/easy? Etsy Pine Bark Fines

  • ewwmayo

    Reptibark is nice but it's just way too expensive! Hopefully you can find a much cheaper bark to use.

  • mblan13

    Teener, If you add your location to your Screen name someone near you might be able to direct you where to find some.

  • mmauenn

    Could zeolite be used as an alternative to perlite in the 5:1:1 mix?

    I was at the store to buy pumice and they were out of stock. The sales person suggested zeolite and so I thought I would try it.

    I haven’t found many articles on zeolite in potting mixes online.

  • Sergey Varlamov

    In regard of soils, one of the differences between perlite and zeolite is that the former holds no water at all, just provides aeration, while the latter holds some water (in addition to large cation exchange capacity), and it helps aeration too. So, one can in principle use zeolite in 511 mix but then they should reduce amount of peat. Same about pumice vs perlite: the former holds water.

    If I recall correctly, someone in this thread posted earlier a couple of very useful youtube links about testing of soil ingredients. Here they are:

    https://www.youtube.com/watch?time_continue=14&v=Mt_a7g6C2Ls

    https://www.youtube.com/watch?v=zJuRmunExtk

    enjoy :)

  • Sergey Varlamov

    Just checked the videos to refresh my own memory and realised they don't include zeolite! I thought they did.

    I do use zeolite (~1/3 by volume) by myself in bonsai and succulent soils as it is the easiest and cheapest to obtain here in Oz. Zeolite performs roughly as well as pumice but it is much heavier. Coz other ingredients vary, I usually do a test: fill a few smallish plastic pots with a new batch of soil mix, place them next to my plants and each day I empty one pot to check how soil dries. For acceptable soil, it should dry within a couple of days max in fine worm weather.

    Also, according to the videos, perlite does retain water too, about the same as sand, apparently as trapped between particles rather than absorbed, which means particle size matters. Here one bag can have perlite of 1-3 mm size (not marked), while another bag from the same supplier will have 2-5 mm perlite. Watch out.

    cheers

  • mmauenn

    Thanks for getting back to me. I’ll have a look at those videos you posted.

    If zeoite holds water would it be a suitable replacement for turface in the gritty mix?


  • mmauenn

    In the 5:1:1 mix, if I used zeolite in the normal ratio, does that mean I would have to water less frequently?

    Half my plants are inside and half are outside. I’m in Sydney and the outdoor pots are drying out so quickly I am now watering my 5:1:1, 2-3 times a week.

    You also said it holds the water internally, does it mean that when use a dowel test, the dowel may come out dry but may still have a lot of water in it.

    Thanks for answering my questions, I’m very new at gardening and also very interested in trying new things.


  • Sergey Varlamov

    I have no experience with turface as it is not even known here in Oz. According to this forum, turface holds a lot of water, which somewhat contradicts to the video results. But one has to bear in mind that the product varies from one supplier to another, so yours can be quite different from your neighbor :). So, without turface, I use zeolite, pumice, DE, all as turface replacements but do tests to determine their amounts in mixes. Now it comes almost like gut feeling :). Although not ideal, but I use zeolite also as a replacement to turface+granite combination in 311 mix. Works for my plants.

  • Sergey Varlamov

    Ah, overlooked your other questions.

    You water when plants need it, not after certain amount of days :).

    Frequency of watering can vary a lot depending on many factors other than soil itself. Important thing is to ensure that soil mostly dries between watering which should not take longer than 3-4 days in the worst case. Longer will hurt roots. It depends on plants too. Most succulents like staying in completely dry soil for many days if not weeks, while leafy plants may need water when soil is still a bit wet. Sure sign to water them is soggy, droopy leaves.

    I used to have a watering spreadsheet to help me remember when I watered what but now I judge by rough pot weight if there is any water left and a plant needs more. I don't find dowel test useful for coarse soils with relatively large particle size of 2-4 mm. Stick comes out dry anyway, quite possibly coz most water is stored internally as you said . I have electronic moisture meter and even right after watering it often shows "dry" in such soils.

    One interesting thing I came across recently not mentioned in this forum is what time of day to water. This webpage says because plants dont do photosynthesis at night, they do NOT use, and don't need, water at night too: http://guide.makebonsai.com/how-to-water-bonsai. 

    If it is true, then one should not water plants, no matter how dry they are, close to sunset but rather leave it till morning. It is my practice now, so far so good.

    BTW, not sure if it is appropriate to leave contact details here. I am in Sydney too, in St Peters, you can call 0422345054 with any questions but I am also a beginner, growing plants for a couple of years only.

    cheers


  • illsstep

    I would not share a personal phone number in a public online forum, period.

  • mmauenn

    @sergey I am in the same area, in Marrickville.

    I understand watering only when the plant need it and not on a set schedule. What I meant was the plants are needing to get watered 2-3 times a week depending on the weather.

    I have not been using a dowel lately as I can judge now the weight of a dry pot vs wet pot. But with new planting media, I will have to study and observe when the pot is dry.

    I have read that it’s not good to be watering late in the afternoons but my schedule does not allow me to water in the mornings.

  • jodik_gw

    This article is still, after more than a decade, my go-to source for container growing knowledge, and I'll never be able to properly express my thanks to Al for sharing his knowledge with the rest of us!

    This article, among others Al wrote, really should be tacked permanently to the front page of this forum, in my opinion.

    Whether I use the recipes for mediums exactly as written, or I change them up a bit to meet my own needs, with respect to micro-environments, this is still the base of knowledge I use. The science couldn't be sounder or more logical!

    So, once again... thanks, Al! Still growing with success here in the Midwest! :-)

    tapla thanked jodik_gw
  • tapla thanked bragu_DSM 5
  • halocline

    Well, someone is finally trying to make money off the "Gritty Mix" (on Etsy), made to order no less! People have told me to do the same; but waaay too much work.

    I guess you'd have more time to make soil for other people; if you didn't have 100+ plants of your own to worry about lol.

    GOOOOOD LUCK!! (Product pics look good.:-)

    Rob


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  • Sergey Varlamov

    Hi everyone. Not long ago I posted a question about my small dying picea tree which I intend to grow into bonsai. There was no comment on that. Maybe, no one knows why it is dying, or maybe I posted the question in the wrong place: it was in water retention XVI by oversight. I am reposting my story here in hope to hear something useful to save the tree.

    I bought my picea on post Xmas sale and it was ~50cm tall, looking healthy, with very bushy top (pic 1 after cutting off the top). I repotted it without much root cleaning to keep most original soil with fungus, which I read Picea, like other pines, needs. I planted the rootball with old soil into gritty mix, mostly pine bark fines with seramice, with a bit of gravel, see in pic.2 very "gritty" indeed :); trunk is ~1/2" at the bottom). I used a biggish pot to let it grow freely for a year or two. I also cut the top to encourage lower branches growth but it never happened. Water it when the pot feels light, ~ weekly (it is early autumn here in Sydney) by bottom watering in a bucket, then drain well by keeping the pot at ~45 degrees for a while. Use diluted Nitrosol liquid plant food every two weeks. Keep it on sun for 2-3 hrs, then half shade.

    Despite all my care (or coz of it ? :), the picea never showed any new growth but started developing warning signs for last month. Those few thin branches started dying. Their stem turns from brown to greyish-green and gets soggy then dries out. See in pic 3&4, that branch in front which is dying now, with grey stem. Other branch died a few days ago. Only three normally looking branches are left. But I am afraid they are facing same fate. I am tempted to remove the tree from the pot to check the roots, trim them shorter and repot into new soil, but afraid to disturb it in late autumn and make the matter worse. Anything suggestion how to rescue my picea? Thanks and cheers

  • Joshua K

    Hi everyone!

    After thoroughly going through Al's advice on house plants and container mixtures, I've determined that almost all of my plants are dying because of my overwatering them (and Kelso, one of my kittens, taking a leak in my ficus elastica pot), and having them sit in garden soil instead of even a poor potting mixture (which is quite common where I live, in Bangalore). The perched water under all my pots was revelatory, and made me a believer in a respectable potting mix.

    So I did a bit of my own research on what plants need from soil, what makes good soil good (in the immediate context, it's 30% air-filled porosity or AFP, as also confirmed in Al's posts), how to crudely measure AFP, and what I could use as substitutes for the 5:1:1 and gritty mix. Almost everything seemed to conform to Al's advice, but it was never thoroughly explained why, which makes customisation a little hard to do, especially since most of the constituents (like perlite, coco husk chips since pine bark fines are nowhere to be found here) for the mixes are prohibitively expensive here in India. It's just coco peat and wholesale expanded clay aggregate that's relatively affordable here.

    Does anyone here know what would happen if I simply skipped one or more of the coco husk chips, granite grit, perlite from these mixes?

    I should probably tell you what I'm working with now:

    • I live in Bangalore (average temp is about 25 deg Celsius, but inter-day varies from 10-25 or 20-35 deg Celsius in winter and summer, 11-13 hour days, relative humidity of 50-75%, and with moderate to heavy rain 3-4 months yearly)
    • I have pots both indoors (moderately lit), and on my west-facing balcony (that gets quite hot and sunny by 5pm in March-May, and gets drenched during the rains)
    • I'll be gone on a six-month work trip during which a neighbour with zero plant experience will be (over) watering them once every 1-2 days (and my plants should be able to survive this time!)
    • Also, since I'll be buying constituents in bulk to make a total of about 150 litres of potting mix, keeping things simple like having a single mixture for all my plants helps me keep cost and effort reasonably low

    I have about 2-3 weeks to repot all my plants before I''m gone, and was hoping one of you kind souls here could help me :)

    Cheers and thanks a lot,

    Josh

    PS: I've originally posted here too: [https://www.houzz.com/discussions/help-needed-with-custom-potting-mix-dsvw-vd~5308077[(https://www.houzz.com/discussions/help-needed-with-custom-potting-mix-dsvw-vd~5308077)

    PPS: In terms of cost per litre of material, expanded clay aggregate and granite grit are about two-third the cost of coco husk chips here, while perlite's about 2-3 times as expensive as the clay/granite.

    Can I skip one or more of the pricier constituents of the mix while still getting a good enough soil?

    For example, I was thinking of using just the clay aggregate and a little granite grit, while skipping the organic matter entirely to maybe make re-potting easier.

  • Joshua K

    Okay, so I've gone through the nine hundred-odd comments here on this instance of the thread, and sort of figured most of my problem out.

    In the short term, for the next year, I'm going to try a 85-90% biochar and 10% coco peat mixture. This seems to be the best option in terms of cost and meeting aeration, drainage, and water and nutrient retention requirements. I'll of course have to break up the biochar lumps and screen them to get a size between 3-6mm.

    If all goes well, then next year I might use a mixture of 3-6mm calcined clay (screened down from 2-8mm), 2.5-4mm granite grit, and maybe a little biochar depending on how slow it is to break down, as I'd like my gritty mix to be nice and sturdy.

    Thanks to everyone here , especially Al, Rob, and those who kept pitching in with their useful questions, experience, and advice.

    Hopefully, I'll be able to get back to you all with conclusive results (good or bad).

    Cheers!

    Josh

  • westes Zone 9a California SF Bay

    @Joshua K, I think you need to tell us what kind of plants you growing. Are these water lovers or are these plants that like dry conditions like succulents?

    I think 85% biochar makes no sense. Charcoal is normally found in amounts 1% to 5% of healthy soils, and you would want to limit to that small percentage.

    Does the expanded clay you have access to retain its shape or does it break down over time? What is the size of those particles? I think the round shape of these is not ideal. I was going to suggest you contact cricket fields in your area and see what material they are using between the mounds to drain water during rain. Maybe you get lucky and find one that uses Turface or a similar product.

    Given your time limitations, you do not really have time to test things out, and you are going to be using a fairly experimental soil. I think you are going to need that neighbor to take some photos for you so you can adjust watering schedule remotely.

    I would try to keep the organic component of the soil below 30%, to prevent compaction, and given your very limited choices I might experiment with a soil that is:

    * 3 parts coconut coir

    * 4 parts expanded clay aggregate

    * 2 or 3 parts granite/grit

    The coconut coir would hopefully have good water release characteristics to the roots, and in the mix that I am using above would be never more than 33%. The expanded clay would absorb a lot of water and make it available for a long time. The clay also dramatically improves the ability of the coir to rehydrate if things become too dry. The granite would be for drainage.

    That is not the mix I would use long-term, and if you had more time I might spend time looking for substitutes. But since you are out of time my guess is that something like the above should work to at least keep the plants going during your trip.

    Also, you are going to need a fertilizer strategy, because this soil has no nutrition for the plants. If the plants are watered three times a week, I would make one of those waterings a fertilizer watering. If using FoliagePro 9-3-6, the dose might be around 1 teaspoon per gallon of water.

  • tropicofcancer (6b SW-PA)

    A few ideas for you Joshua:

    Look for a local bonsai club. They have to suffer through this soil mixture decision and they may have a good solution for ingredients and sources in your area.

    Crushed brick is commonly available (at least in Kolkata) and cheap. You will still have to sift it. My father pays someone to get it from construction sites and sift it.

    You have to be careful with coconut products since they may be high in salt and you may have to wash it several times. Hopefully if is sold for plants then it is already washed properly.

    I have heard rice-hulls or peanut shells are also used in India for increased aeration. Both breakdown slowly.

    How porous do you think is the expanded clay? Perhaps like brick. I would go for a 3 clay to 1 coco-peat. May be a bit of grit mixed in too - perhaps 3:1:1 clay, peat, grit.

  • Joshua K

    Thanks westes and ToC!

    The plan really is to get a decent gritty mix going based on Al's recommendation as I didn't want to deal with screening or cleaning out broken down material during repotting every year. Hence, peat substitutes are not an option for me, unless I'm trying to do a proper 5-1-1 mix.

    However, there've been some developments -- I decided to bite the price-bullet and buy expanded clay aggregate that I'll screen to keep only particles larger than 3mm. Since it was a bulk purchase, it's more than enough volume to fill all my pots, but I'm going to wait until I've been able to find the grit, which is turning out to be harder than expected. Aquarium shops do have gravel, but selling at 1000x times the price of bulk gravel, which again is nowhere to be found containing the right sized particles. It's probably because most construction projects here use sand that's way smaller than 2-4mm, or use crushed stone that's 10mm or larger.

    The twisted reason why I decided to use so much biochar was, other than getting desperate, I stretched Al's logic a bit too far, perhaps. He had mentioned that it'd be a good substitute for expensive perlite, and in another post mentioned than it'd be a decent substitute for the elusive pine bark fines. I guess this wasn't a situation where I could simply put two and two together and decide to use 90% biochar.

    In the meantime, though, my business trip shifted, giving me another month to figure all of this out, and I've been able to hire help to fertigate my plants when I'm gone.


  • halocline

    WOW! Lots of new names & faces here.

    Joshua - Sounds like you might use plain Biochar. I make my own "Activated" Biochar which I use as a soil additive. I first heard of it from Jericson Pastor on the Adenium Forum, then learned how to make it from Josiah Hunt; founder of "Pacific Biochar". At the time they didn't ship East of California; but now they sell 3-4 different kinds on their site: https://pacificbiochar.com/

    Small grade crushed Lava Rock is also a great alternative material for a gritty type soil mix.



    I've just read the last 4-5 posts here tonight; so I don't know where you're at, but as westes said above about fertilizing w/ FP 9-3-6, the measurement for using it every time you water is- 1.25ml/Gallon of water (I also add about 0.75ml of "Protekt"). If you're going to fertilize at every watering, you have to remember to give your soil a thorough flush every 7-10 watering's. Also, don't fertilize when the temps are really hot (above 85-90).

    Nice to meet you both.

    Good to see you as well toc. ;-)

    Rob

    (Adenium S1 w/ transplant ferts)


  • bragu_DSM 5

    just too much good info to trickle to a distant page ...

    tapla thanked bragu_DSM 5
  • TheStar

    As winter has arrived I have some plants dropping leaves. Some of the leaves land in the gritty mix. Is it okay to just let them dissolve into the mix or is it better to remove them?


    Thank you all for sharing so much information and wisdom! HAPPY HOLIDAYS!

    tapla thanked TheStar
  • tropicofcancer (6b SW-PA)

    My take is that after spending money, time and all the learning to create a better mix I would rather keep it clean off things I do not want in there. I do sometimes put another small companion plant or moss but I like to keep it clean of things that are really not supposed to be there. A few leaves here and there is not going to harm so much though. And being on the surface it will take a while for it to actually decompose enough to mix into the soil. But then I am picky - I mean literally picky :) I use bent tweezers to pick even the smallest foreign material from the surface - as far as my old eyes can see. I try to do that for all my potted plants with gritty or 511.

    tapla thanked tropicofcancer (6b SW-PA)
  • PRO
    tapla

    I think that's good practice. Anything decomposing on top of the soil serves as sustenance and a repository for fungi and fungal spores. Keeping the entire growing area clear of decomposing plant parts is good practice. Good greenhouse operations are fanatical about cleanliness.


    Al

  • Allison H

    Hi everyone! I really love all the information provided! Sorry if this is a redundant question that has already been answered in the above comments: I just don't have time to go through all 900 of them. :) Al, your recommendations on soil creation make a ton of sense but I'm a student in a small apartment, and I don't really have the time or space to create my own soil. I have a FLF that's about 6 feet tall, and I am really hoping to repot him in the spring (because I've had him for 4 years and never changed the soil). Can you recommend (albeit subpar) a store-bought mix or maybe even a mix of two different but similar ones, that way that I can buy something mostly premade to plant with?


    The local Lowes has an Orchid mix that looks kind of similar to your gritty blend, and they do have pine bark and a tree/shrub mix. Would you favor any of these over another? I posted pictures of the different soil options below (the first is the tree/shrub mix, the second is orchid, and the 3rd is the pine bark). Or should I just stick with regular potting soil and place a wick? The new pot will be 12" in diameter (I think the current one is 11" and I plan on cleaning up the roots and replacing all the soil.


    Anyway, he's been really healthy to date and I even pruned the top last spring and it did excellently. So I figured tackling a repotting would be the next step. Thanks in advance!


    Allison




  • xclumsygrdner

    Is this OK for 511

  • PRO
    tapla

    Allison - So sorry for missing your post. My younger brother passed in mid-Dec, so there wasn't much time for fun stuff like being here.

    I'd be thinking a larger pot than what you're planning. You can make most potting soils work well if you add a large fraction of perlite (preferably media grade or coarse/propagation grade) to your mix and plan ahead to include judicious use of ballast in the bottom of the pot. You can actually remove more than 90% of of perched water from soils that support as much as 6" of perched water. Ballast won't resolve issues like insufficient aeration or compaction, but perched water is the factor that robs more of your plant's potential than any other factor related to physical properties in soils most of us would still consider to be on the 'usable' scale.

    Please read this so you're up to speed, then we'll make a plan if you're up for it. I'll likely ask for some more images of the bark - spread out on white paper to get a better sense of how to best use it.

    It appears to have a lot of sapwood/heartwood in it, but it can still make a strong contribution to a medium, even if that's the case. We just wouldn't use it in the 5:1:1 ratio. Probably no need to spend the $ of the orchid mix. Pine bark, perlite, and lime, + a little peat (maybe) is going to be all you need. You can by the lime in a 50 lb bag, or - ESPOMA sells it in 10 lb bags for about the same price as 50 lb by other packagers ....... but the bag IS prettier. ;-)

    Don't know if you've read much of the other things I talk about (like FLFs), but it wouldn't take me long to convince you to make a plan you can execute around Father's Day. Hopefully, you already know why, but if you don't, I'd be happy to explain


    **********************************************************************************


    Xclumsy..... - great choice of usernames. If all the bark is that size, it's quite large, but you can still make it work. Where do you live (want to get a sense of what ingredients might be readily available near you. Look at the image I left for Allison, please. The bark at 12 o'clock is screened to 1/8-1/4", so it should give you a sense of size for the rest of the stuff on the paper. The bark at 3, 6, and 9 are all from different packagers and about ideal for the 5:1:1 mix. Note it's quite a bit finer than what you have. In the middle is the dry 5:1:1 I use. Can you also provide an image of the bark you have on a sheet of paper with something to help estimate its size gradient. An aspirin (if you figure out a way to present it so I can see it) would work really well.

    Al

  • xclumsygrdner
    I live in Lexington KY.

    The only place that sells pine bark fines sells them by the truck load. Unfortunately I'm a balcony Gardener and my land lord wouldn't approve!

    I managed to find a product called Claybreaker that is mostly composted pine sapwood with some bark mix up n. Composed black. I mixed in very generous perlite.

    The product above is what little I managed to pick out of a bag of pine bark nuggets, but I gave up on that.
  • jbclem 9b Topanga, Ca

    I've been using Earthgro Groundcover Bark for years until recently....but Home Depot no longer carries it and Orchard Supply has closed. So far the only solution I've found is to buy the bags of Earthgro Bark (medium or large chunks) and run it through an electric mulcher/shredder. But the result isn't chunks, it's shredded bark. Since that's all I have, I'd like to ask is it ok to use the shredded bark in the potting mix?

  • Allison H

    Al, thank you so much! I'm really sorry to hear about your brother, that must be incredibly tough on you and your family. Wishing you lots of healing. Just want to say it's really kind of you to take time to help all of us out, and I appreciate how much wonderful information you've shared on these forums. Just curious, does your growing knowledge come from experience alone or do you have a baseline education in plant science or botany? This is the kind of information is golden, and so hard to find! You could really have your own website with all of this advice! I remember reading one of your forums several years ago when I first brought my FLF home, and I've referred countless people towards these pages for help with their container plants. :)


    Thanks for the links to the ballast and water-retentive soils, I've never really understood that concept before but it makes a TON of sense now. In that case, I will definitely need a bigger pot so I can accommodate some ballast. I was actually able to find someone locally who thinks they can provide me with some pine bark fines in the spring, which *should be* about 1/4-1/2" or so. When I get it, I can definitely post a picture of it on a white background. And I can definitely get the perlite and lime and peat. Do you have an estimate for how much of each component I'd need to repot this guy, or what size pot would work best to include the bricks when June rolls around? I'm all ears for whatever other recommendations you have!


    Here's a picture of it from this summer after I pruned the top parts off. Since then it has grown two long branches on each stalk from the cut point, and is taller than me!




  • xclumsygrdner
    My condolences for your loss Al. :( Thank you for your hard work and continued help even at this tough time.

    I didn't end up getting pictures today because I think I might have found actual pine bark fines at Kings Gardens. This locally owned landscaping supply and Garden center has been closed until now, and is still technically closed since it's too cold to sell plants. But someone answered when I called. The lady I spoke with was pretty certain they would get pine bark fines next week. I will post pictures when I get some.
  • xclumsygrdner
    My condolences for your loss Al. :( Thank you for your hard work and continued help even at this tough time.

    I didn't end up getting pictures today because I think I might have found actual pine bark fines at Kings Gardens. This locally owned landscaping supply and Garden center has been closed until now, and is still technically closed since it's too cold to sell plants. But someone answered when I called. The lady I spoke with was pretty certain they would get pine bark fines next week. I will post pictures when I get some.
    tapla thanked xclumsygrdner
  • enz1ey
    Hey guys, I’ve been pouring over the various Al’s soil mixture posts for the last several weeks, and it’s a bit overwhelming. I think I’ve managed to learn more about soil composition and behavior than I ever thought I would, and using the materials available to me, I’ve put together what I think is hopefully a decent gritty mix. Does this look alright? It’s currently in a 5-gallon Home Depot bucket. I haven’t found a decent source for pine bark fines, so I used Repti Bark sifted with a Bonzai sieve.
  • mblan13

    Two thumbs up.

    tapla thanked mblan13
  • nycfigs

    Hi Al. Danny Gentile (NYCfigs) here. Please accept my apology for posting here but I've been trying to contact you through Houzz. Wanted to discuss an topic off-thread. I don't think the messages are going through. Could you email me at danny@nycfigs.com. Would appreciate it very much. As always, love your posts. Thank you.

  • mblan13

    Bumpity-bumpity-boo!


  • Skip1909

    Hey, I made some 511 over the winter, using Agway pine bark mulch screened over 1/4" hardware cloth. I used Kellog organic container mix for 1 part, and 1 part perlite. I added the recommended amount of pelletized dolomite lime. Things are not growing well. Seedlings in 2.5" x 5" deep cells are like frozen in time, and holly cuttings in 1 gal grow bags sitting on the ground are yellow a little pale looking. I fertilized with foliage pro at the lower rate on the bottle, 1 tsp/gal. Is it the fact that the pine bark was not composted or aged? Or the Kellog soil? What can I do? Im at the point where I am considereding dumping it, screening it over bug screen and mixing it again using a different peat for the 1 part.

  • PRO
    tapla

    More fertilizer ....... especially if the chlorosis is most severe in older foliage, or worse, older foliage is being shed. Assuming you're flushing the 5:1:1 regularly, you should be able to fertilize with 9-3-6 at at 2 tsp/gallon every 3rd time you water.

    Al

  • edweather USDA 9a, HZ 9, Sunset 28

    They should be growing well. Your mix sounds a bit fine at 1/4", but that's not the issue. I don't know much about holly. What seedlings are you growing. A pic or two might help.

  • Skip1909

    The seedlings are perennials Geranium maculatum, Verbesina alternifolia, Thermopsis caroliniana and others. All the plants are outdoors, so its certainly possible the mix isnt the issue, but I wanted to rule that part out. I have the seed trays in a low tunnel under 1 layer of 0.5oz row cover fabric and 1 layer insect screen, the ends of the tunnel are open with just screen. The floor of the tunnel is lined with nonwoven geotextile fabric. It might be too hot, too much sun, too much rain, etc, but I had some success starting seeds this way last year with a similar set up and bagged soil. The holly cuttings are in grow bags up against the north facing side of a solid fence, not in the low tunnel. They get some direct sun in the morning but otherwise only indirect light. They have dropped some leaves. I will fertilize if it ever stops raining.

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