Container Soils - Water Movement and Retention 8/26/21
Hello! This post has 3 pages. Houzz's format won't allow me to post the thread in it's entirety, so the thread will continue in the 2 text boxes subsequent to my OP. It's necessary to repost the thread from time to time because after a given number of replies, part 2 and/or 3 get archived and are difficult to find. I'll try to be better about reposting as soon as the number of posts reaches that point.
I want to thank all the growers and good people who have participated and 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 is to offer information that allows you to avoid an ongoing battle with your medium for control of your plants' vitality, information that will help you increase the reward you get in return for your efforts.
I started this thread about 15 years ago, in March of '05. So far, it has reached the maximum number of posts GW allowed to a single thread twenty two times, which is much more attention than I ever imagined it would garner. Currently, there have been just over 6,200 posts to the singular topic. 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 so often stem from the subject matter are in themselves enough to make me hope the subject continues to pique interest, and the exchanges provide helpful information. Most of the motivation to post 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. 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 them. Also, you will find I use the terms medium/ media and soil/ soils interchangeably.
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 by the grower. Vitality is something you have much, perhaps nearly total control over. The visual signals we get from the parts of the plant we CAN see allow us to take measure of the condition of the roots and the plant's overall vitality. Soil choice and watering habits, have a very significant impact on root health. As you read, keep in mind that good root health and root function are an essential PREREQUISITE to a healthy plant. We 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 remediation 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's 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.
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' container medium, but also points to the fact that not all growers look at container media from the same perspective, which is why growers so often disagree on what makes a medium 'good, bad, or somewhere in between. I hope you find it thought provoking:
IS '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 X a quality or suitable medium?" How do we determine if medium A or medium B is a good one? And before we do that, we had 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 (s)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 medium 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 medium 'good' from the individual grower's perspective; but let's change our focus from the pointless to the possible. We're really only interested in the comparative degrees of 'good' and 'better' here. It would be presumptive to label any medium "best", though '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 medium 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 medium 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 should be, at a minimum, that you can water properly. This means at any time during the growth cycle you should be able to 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 due to (take your pick) an excessive volume of water or too little air in the root zone.
I think it is very reasonable to withhold the comparative adjective, 'GOOD', from media that can't be watered properly without compromising root function, or worse, suffering disease from one of the fungaluglies that cause root rot. I also think anyone wishing to make a case from the plant's perspective that a medium which can't be watered to beyond saturation w/o compromising root health can be called 'good', is fighting uphill against logic.
So I contend that 'GOOD' soils are those we can water correctly; that is to say, we can flush the medium when we water without concern we would be compromising root health/function due to long term retention of excess water. If you ask yourself, "Can I water correctly if I use this medium?" and the answer is 'NO' .... it's not a good choice .... for the reasons stated above. Can you water correctly using most of the bagged bagged potting media readily available? 'NO', not without work-arounds in place, and we can talk about those.
What about 'BETTER'? Can we determine what might make a better medium? Yes, we can. If we start with a medium which meets the minimum standard of 'good', and improve either the physical or chemical properties of it, or make it last longer structurally, 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 any medium that reduces excess water retention and increases aeration ensures better potential for optimal root health than media which only meet some one's individual and arbitrary standard of 'good'.
All the plants we grow, unless grown from seed, have the genetic potential to become beautiful specimens. It's easy to see the absolute truth in the idea that if you give a plant everything it needs to prosper it will flourish. 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 discussion, let's examine what the plant wants from its soil. It 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, 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 medium that is evenly damp, never wet or soggy. Giving a plant what it wants to flourish and grow doesn't include a medium half saturated for a week before aeration returns to the entire mass, even if we only water in small sips. Plants might do 'ok' in some water-retentive soils if the grower is highly skilled, but in order to actually flourish as plants are genetically programmed to do, they would need to be unencumbered by media which do not remain wet/ soggy for extended periods.
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 addressing those influences inhibiting the plant from reaching its genetic potential. Even if we are able to provide every other factor that influences plant growth/ vitality perfectly, it could not make up for a substandard medium. For a plant to realize its full genetic potential, every factor has to be perfect, including the medium. Of course, we'll never manage to get to that point, but the good news is, as we get closer and closer, our plants get better and better; and almost certainly, we'll find our growing experience more rewarding.
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 has a future full of potential, where a $10 plant in a 2-bit has only a future filled with limitations. ~ Al
CONTAINER MEDIA – and WATER RETENTION
This is where we get to the meat of the subject. As container gardeners, our first priority should be to ensure the media we use provide adequate aeration for the intended life of the planting, or in the case of perennial material (trees, shrubs, garden perennials), from repot to repot. Aeration/drainage is arguably the most important consideration in any container planting. The soil is the foundation 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 (or make, in the case of 'media/ soils') soils or primary components with particles larger than peat/ compost/ coir/sand/ top or other traditionally 'fine' ingredients.. 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 will also hit heavily against the futility in using a “drainage layer” of coarse materials in attempt to improve drainage. It just doesn't work. All drainage layers do is reduce the total volume of medium available for root colonization. A wick can be employed to remove water from the saturated layer of medium at the container bottom, but a drainage layer is not effective. A wick can be made to work in reverse of 'self-watering' pots.
CONSIDER THIS IF YOU WILL:
If we agree we should avoid ingredients that are phytotoxic (toxic to plants) our primary consideration when building/buying a container medium should be the medium's structure and its structural stability. Size of the particles that make up a medium, the ratio at which they are combined, and the long term durability (resistance to breaking down into smaller and smaller particles) plays a primary role in determining whether a medium is suited or unsuited to the application. The medium 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, which are a 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 media are so limiting. 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/ retention of water in container media.
There are two forces that cause water to remain in or move through soils – one is gravity, the other capillary action. Gravity needs little explanation because all things are pulled toward the center of the earth. For this writing I would like to note: Capillarity is a function of the natural forces of adhesion and cohesion. Adhesion is water's tendency to stick to solid objects like particles and the sides of the pot; it is the reason water can stick to the inside of your vertical shower door. 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. Capillary action is adhesion + cohesion, forces 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 force of gravity is equal to the capillary attraction of the fibers in the paper.
There will be a naturally occurring "perched water table" (PWT), also referred to as a 'perched water column' in containers when soil particle size is under about .100 (a little smaller than 1/8) inch. It is created whenever the capillary pull of the medium (remember how the water climbed up the paper towel and defied gravity) surpasses the Gravitational Flow Potential GFP (weight of the water column in the pot); therefore, the water does not drain, it is said to be 'perched'. The smaller the size of the particles in a medium, the more surface area there is for water to 'stick to', so the greater the capillarity and 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 medium on top of a coarse drainage layer, where again it will not drain. It is water that resists gravity whenever the force of capillarity is stronger (when particle size is too small) and will not allow the PW to drain from the portion of the pot it occupies. It can evaporate or be used by the plant, but ambient physical forces will not allow it to drain naturally.
Imagine we have five cylinders of varying heights, shapes, and diameters, each with drain holes. If we fill them all with the same medium mixture, then saturate the medium, the PWT will be exactly the same height in all the containers.
This saturated area of the container is where roots initially seldom penetrate and where root problems frequently begin due to a lack of aeration and the production of noxious gasses which cannot escape waterlogged media. Water and nutrient uptake are also compromised by lack of air in the rhizosphere (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 medium that supports perched water, taller growing containers will always have a higher percentage of unsaturated than squat containers when using the same medium. The reason: The level of the PWT will be the same in each container, with the taller container providing more usable, air holding above the PWT. From this, we could make a good case that taller containers are easier to grow in.
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Container Soils - Water Movement & Retention XIV
Comments (164)Thanks for the kind words, B&C. In Mississippi, Memorial day would be a good target date for repotting the fig. Hibiscus need an annual repot. Do that toward the end of March, before it starts growing in earnest. Apple and most deciduous trees should be repotted just before or at the onset of spring budswell. Cactus - ask the cactus experts at the cacti/succulents forum. Desert rose - in Mississippi - June Umbrella plant - June There are ways to mechanically limit the amount of perched water a planting will hold, even if you're using a very water-retentive medium. Eliminating all or most of the perched water allows the grower to use media that would otherwise be or border on the edge of unusable. This outlines ways to cope with heavy (water-retentive) media Another effective way of dealing with media that hold too much water is through the use of ballast. You can read more about that technique here: Ballast ..... For now, checking your planting's moisture level regularly with a 'tell' will make a difference in your plant's appearance and level of vitality. Here's something I wrote about that: Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support good root health, which is a prerequisite to a healthy plant. Watering in small sips leads to a build-up of dissolved solids (salts) in the soil, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor. In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water. Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'. One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue. Al...See MoreContainer Soils - Water Movement and Retention XX
Comments (150)Yes, I stated that I'm not worried about the aluminum, all the same I won't use aluminum sulfate either. Although it may be safe, I worry about toxic levels. Just because lead is in all soils doesn't mean it's a good idea to add more. Same with aluminum. And if you mix turface without a mask, you will be exposed to it. As far as water absorption Axis noted that turface holds 95% of it's weight in water. Pumice only holds 15% and DE holds 142% Try diatomaceous earth in your tests. Optisorb is about the largest size available to home gardeners. Axis makes an excellent size, but is for commercial use only. Numerous studies document it's use as superior to most other amendments. Such as " Effects of diatomite on soil consistency limits and soil compactibility" by Ekrem Lutfi Aksakala, Ilker Anginb, , , and Taskin Oztasa Or "Effects of diatomite on soil physical properties" by the same authors. Also "Sustainable effects of diatomite on the growth criteria and phytochemical contents of Vicia faba plants." Mona M. Abdalla* Department of Botany, Faculty of Science, Ain Shams University, Cairo, Egypt. The Axis company also has great info on all amendments. As far as particle size, do a test. Fill a pot with sand, and one with gravel. Stick a pole in, and see which one gives more resistance. It seems to me gravel would. But I might be wrong? I don't know physics well enough to figure it out on paper. Ah and pumice is further dashed to the ground and called a fake, not a single user rises to defend. Well we can agree to disagree, my day job is a laboratory researcher,or was, I'm retired. If turface has various pore sizes then it is not very well made. Thanks for pointing that out. So you do not believe the manufacturer? Controlling pore size in fired clays is often accomplished with the use of polymers such as Polyethylene glycol. This process is extremely important to control how well purifiers work, or how well they hold up with the addition of salts. You are incorrect about the pore size. Yes pore sizes differs, but that process is used to make different products, and is very controlled. Turface is meant to have small pores size or it would ineffective in it's intended use. The porosity of fired clays is extremely important to have a consistent product such as fired brick used to built houses. Varying pore sizes will compromise the strength of the brick. Selling a product and manufacturing one are very different things. The pore size I reported is for calcinated clay. Range of pore sizes is from .1 -.01 microns. Median is .045 . Plants need a .2 micron minimum pore size to utilize. This info is from a study by Andreas Kalytta-Mewes, Kathrin Mattern, and Armin Reller University of Augsburg, Chair of Solid Body Chemistry Georg Armbruster Soil Laboratory. The pore analysis in the study was conducted by Quantachrome,Bavarian Institute of Applied Environmental Research and Applied Technology. Of course it appears none of these sources trump Al. Who has not provided any data at all to back his claims. Please prove to me that pore size is bigger, thinking Al is right because you sell clay products is not proof. After saying all this will turface work? Yes, it will. Works pretty good! Is it ideal? No, it's not, but what is? It's still worth trying for sure. It didn't work for me, but that means nothing. it has worked well for others. It would be nice if it allowed easier access to stored water, but it does store water, and air, and it lasts a long time, maybe 20 years. That's decent. It's a decent product, or appears to be. It would not be on the market if it didn't work. I know it's not meant for potted plants, but it is meant for grass. DE seems a better product, it has it's own problems. it is marketed though for plants more than ball fields, although it is marketed for that too. It's marketed for large commercial gardens. I use it in my garden. I use turface too for my grass, works well. Just not that well in pots for me. All i said that it didn't work for me. Sorry blame me, it's what you usually do when the mixes fail, you blame the poster. Many have said DE doesn't work for them. I actually believe them. All gardening is local. This post was edited by Drew51 on Mon, Dec 29, 14 at 15:33...See MoreContainer Soils - Water Movement and Retention XVI
Comments (164)Hi Al and others, I would appreciate advice on saving sick/dying Picea glauca, in pic.1, please. I bought it on post Xmas sale and it was ~50cm tall, looking healthy, with very bushy 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 2-3 weeks. Those few thin branches started dying. Their stem turns from brown to greyish-green and gets soggy before dying. 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. Anything I can do to rescue my future picea bonsai at all? Thanks and cheers, Sergey...See MoreCONTAINER SOILS - WATER MOVEMENT and RETENTION XXII
Comments (1044)Over the years, I've saved a ton of word documents that answer common questions. One of those documents is about particle size: Particle Sizes (ideal) In a perfect world, the mineral fraction for use in the gritty mix would range in size from 1/10 - 5/32" (.100 - .156", or 2.5 - 4.0mm). The bark fraction would be slightly larger to allow for some breakdown over the life of the planting ........ from 1/8 - 1/4 is about ideal (.125 - .250" or 3.25 - 6.25mm). For the 5:1:1 mix, particle size should be from dust to 3/8". (0 - .375", or 0 - 4mm), with most of the bark ranging in size from 3/16 - 3/8" ( .188 - .375", or 4.8 - 9.5mm). The perlite should be on the coarse side - something like the all purpose or super coarse shown below. If you read the size gradation next to the images, you'll see the images are misleading as the product appears to be much larger than the size listed in print. starter: 1/16 - 3/32 inch (1.6 - 2.4mm) you can sub #1 cherrystone/quartzite if available grower: 3/32 - 3/16 inch (2.4 - 4.8mm) you can sub #2 cherrystone/quartzite if available developer: 3/16 - 5/16 (4.8 - 8.0mm) you can sub #3 cherrystone/quartzite if available turkey: 5/16 - 7/16 inch (8.0 - 11.0mm) turkey finisher: 7/16 - 5/8 inch (11.0 - 16mm) The last 2 sizes of grit can be used as ballast in the bottom of shallow pots by mixing 3 parts of grit to 1 part of your soil; this, to avoid water perching above the layer. The layer should be as tall/deep as the PWT your soil supports. Skip this if using a properly made gritty mix. Al...See Moretapla
10 months ago
chamaegardener (Z5) Northeast Illinois
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Gregório Miranda
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9 months agochamaegardener (Z5) Northeast Illinois
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9 months agoDom
8 months agoMy plants have been thriving after a year of using 511 and gritty mix. Thanks @tapla and to the other members of this forum. Here is my philo collection in gritty mix
Since it's mostly dry and warm here in Sydney, im using pine bark fine, diatomaceous earth (DE) and pumice for my gritty mix. Watering every week even during winter and I never had issues with overwatering.
Now I need to make another batch of gritty mix but DE hasn't been available for several months now. I'm thinking of replacing it with either perlite or scoria rock. Which one is better? Thankstapla thanked Domtapla
8 months agoDom
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7 months agochamaegardener (Z5) Northeast Illinois
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7 months agoIs there merit to airpots? Yes. They are designed such that when roots reach the perimeter of the soil mass they are killed by desiccation; then, just as in a branch with the growing tip (the apical meristem)removed, the root back-buds and the new branches hopefully grow outward from the center of the root mass. The added gas exchange due to the perforations in the pot sidewall(s) also helps the soil to dry down faster, which is helpful to root health. Within reason, the media or growing set-up that actually requires watering more often is going to allow the grower to provide plants with a better opportunity to realize more of their genetic potential. They seem to be based on providing more air within the root zone, similar in theory to Als Gritty Mix. They work to some degree in that fashion, but a well-aerated grow medium is the best way to increase gas exchange and ensure the medium doesn't remain saturated long enough to be a serious and cyclic limitation that robs plants of a large fraction of their potential in terms of growth rate, vitality, appearance, and yields where applicable. Thinking it through though, if regular garden soil is used then the only air introduced is when the roots reach the outside of the pot. Yes, the finer the materials used to make the medium, the less effective the air pots will be. But if the gritty mix is used, then perhaps more air would be introduced throughout the root zone? True by virtue of the fact the gritty mix doesn't just have a random macropore here and there between soil particles. The pores are so abundant they link together to form a labyrinth of channels throughout the entire soil column through which air can move ...... and a gas disperses in air more than 10,000 times faster than in water.
I foresee an issue though with overwintering, where sinking them in the garden might introduce smaller undersireable particles into the gritty mix. If the planting is established and the entire soil column is filled with roots, as one might expect the case to be as fall/winter arrives, it wouldn't be much of an issue at all. I'd just take my trusty hemp whisk broom and brush the fine particles away. It works amazingly well for brushing small soil particles and other detritus from the top of the soil.
Al
chamaegardener (Z5) Northeast Illinois
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5 months agoI'm pleased to make your acquaintance, Becca, and thank you for the kind words. All who give advice here like to think it is helping others get more from their growing experience, so it's easy to image how much we enjoy having our efforts validated.
If you have a working knowledge of the concept that drives how the media I use are put together, you might know that if all the particles that make up a medium are larger than 1/10", the medium will for all intents and purposes be incapable of holding anything more than a negligible amount of perched water. The dust or very fine material you inquire about is allowed to remain included in the mix not because it's beneficial or essential to the plant, but because it is more convenient for the grower to water every 406 days instead of every other or every third day.
The gritty mix should be carefully screened to eliminate dust and the finest of particles, and it's would be essential to do the screening if the intent is to do away with as much perched water as possible. If someone is tempted to start adding peat or coir or compost to the gritty mix "to increase water retention" because they "heard" it doesn't hold enough water, they will have eliminated the reason they made it in the first place. I don't mean to get off into the weeds by mentioning the gritty mix when you asked about the 5:1:1 mix, but the point being made is valid for either. When we're implementing the concept behind the media, we're presumably looking to offer our plants the best opportunity we can, to realize as much of their genetic potential as possible. Ideally, the level of dust and fines would be very low - only a % significant enough to provide the grower with watering intervals they can work with. The plants will still be perfectly happy if we situate them in a medium that requires watering several times per day, but we as growers need to compromise when the order of our priorities dictates that having a job is more important than watering plants every day or every other day. Personally, I prefer growing in media that requires me to water a planting about every 3rd day, even though plants might do better in a medium that holds less water.
So, when it comes to media's ability to hold water, less is almost always going to be better (but there will be a point at which too little water will lead to diminishing returns) from the plant's perspective, even if it requires extra time watering and fertilizing more frequently. If that's something the grower can't or won't deal with, it's up to the growers to determine what's right for themselves. Very often we find what is truly best for the plant and what is best for the grower ere mutually exclusive.
Why not make a small amount of 5:1:1 mix with pine bark in the 1/8-3/3 size range, and no peat or bark fines, and try a few plants in that? I guess it would then be a 5:1 mix. Mark the pots as special and see what you find about A) how often they need water, and whether or not you're willing to make the extra effort, and B) how the plants take to it. When you compare the 'experimental plants' to what you know from growing other plants in the 5:1:1 mix, you should have a very good idea about what direction you want to take.
Pine bark, with it's flat particles is somewhat unique in that perlite which is quite fine can get wedged between 2 particles of bark and create a very large pore space, so the size of the perlite is less important when using pine bark than it is when someone is trying to amend peat, coir, compost, ...... with perlite.
Generally speaking, medium is fine for 5:1:1, but coarse will work fine, too. For media with large fractions of peat or other fine particulates, coarse, and lots of it, are the better choice.
Al
RoseMe SD
5 months agotapla
5 months agolast modified: 5 months agoIn science, a fluid is a liquid, gas, or other material that continuously deforms (flows) under an applied shear stress, or external force. Grow media are technically fluid and as such they can be displaced. Displacement is described as the occupation by a submerged/immersed body or part of a body of a volume which would otherwise be occupied by a fluid. When we drop a marble into a glass filled to the brim with water, the marble displaces its own volume in water, so a measure of water equal to that displaced overflows the brim of the glass. When a particle of perlite is added to a container filled with water-retentive medium, the same thing occurs, so the perlite particle reduces water retention by virtue of the fact it displaces it's own volume of medium and the moisture it is capable of holding.
To continue the discussion, I think it's important to understand A) where the perlite particle is located in the soil column changes the degree of it's usefulness, and B) what is meant by the term 'container capacity' (CP), which can be described as the measure of how much water grow medium in a container holds at the moment it has stopped draining after having been watered to the point of complete saturation.
Imagine a 10" pot filled with a medium that supports 4" of perched water at CP. The perlite particles situated in the fraction of the soil column capable of holding perched water (the bottom 4") are very useful in that they occupy space which would otherwise be filled with with medium we know will be 100% saturated with water at CP. Unfortunately, the perlite does little or nothing to increase the level of aeration within the fraction of the soil column that holds perched water; this, because water within the perched water table fills ALL air space, even those that provide small air pockets on the surface of the perlite particles. Since the top 6" of medium is incapable of holding perched water and should generally provide an adequate oxygen supply for most plants, perlite in that fraction of the soil column becomes pretty much superfluous.
Perlite does contain internal pockets of air, but these are not open pores which would add to porosity. Think of someone adding dozens of ping pong balls to a medium to increase air porosity because, after all, 'they are filled with lots of air'. Perlite is much the same. While its highly irregular surface is capable of adding some air porosity to the fraction of a soil column where no perched water is held, we must realize that the amount of air porosity it can add to media comprised of fine particles can be nowhere near the volume of air and medium displaced by the particle. So, adding a perlite particle to any given volume medium REDUCES o/a aeration and continues to do so until there is a volume of perlite so large that there is no longer enough fine material to fill all the air spaces between the perlite particles.
This brings us back full-circle to the idea that, 'if we want to build a medium which provides the benefits of higher aeration and better/more complete drainage, it's essential to start with a very large fraction of coarse material (80% or more), because trying to amend a medium deemed too water-retentive will take us the opposite direction we intended to go before it gets better'.
Notice how the images (page 3) show how adding large particles thinking we're amending media based on materials too fine actually decreases aeration until we get to the "threshold proportion", which occurs at the point there is no longer enough fine material to fill all the spaces between the coarse particles.Al
skysong4
5 months agochamaegardener (Z5) Northeast Illinois
3 months agotapla
3 months ago
trucker's hitch (knots) ^^^
String tied to wire loops, ^^^ which go through holes in the bottom of the pot.
Al
chamaegardener (Z5) Northeast Illinois
3 months agotapla thanked chamaegardener (Z5) Northeast IllinoisRoseMe SD
3 months ago- tapla thanked four (9B near 9A)
Josh
2 months agoSeth
2 months agotapla
2 months agoRose - Perlite is not internally porous in that there is no way air or water vapor can enter perlite's closed cells, which hold the same gasses they held when the perlite was first vitrified. That's why aeration decreases on a per/volume basis when perlite is added to fine material. It's impossible for perlite to provide as much aeration as it displaces because perlite's rough surface is the only part that can create aeration, and it can only be a small fraction of the air in the material it displaces.
Perlite is more effective in bark-based media than in media based on fine materials like peat, coir, compost, sand, composted forest products, ..... . The reason is, a particle of perlite in fine material like I listed will be surrounded by that fine material, providing less aeration than in the medium it displaces; in bark, perlite gets wedged between flat pieces of bark, creating very large air pocket. Lay a playing card on a table so it covers a piece of perlite and notice how much space is created between the table and the card. It is many, many times more than the volume of perlite, perhaps as much as 100x. It's still essential though, if you want to take advantage of all that aeration, you don't shoot yourself in the foot by adding too much fine material. If there are enough fines to fill the large spaces created by the perlite, there is no sense in looking for bark.
Four - Thanks for thinking of us and providing the images!
Josh - heterogeneity isn't necessarily a plus. In fact, it's possible to have less air space in a mixture of particle sizes/shapes than it is in a medium that has a smaller particle size than the average (particle size) of the mixture, if the smaller particles are uniform in size and shape.
You might have some success growing in pine bark only, but don't forget to add the dolomite - CaMg(CO3)2 to bring the pH up to something that better favors the average plant. Once you get a plant to establish in a medium, the roots actually become part of the soil structure. I've seen ficus trees that have been kept in the same container so long that almost all the soil has gassed off and I could look into the pot and see the bottom in places. That's aeration!
As I mentioned to Rose, anything gritty (and not phytotoxic) will work as well as perlite in the 5:1:1 mix. Seramis would work, as would granite chips or formaldehyde foam beads of an appropriate size. I don't know what the parboiled rice hull situation is in France, but that could be pressed into service as a replacement for peat and or perlite when used with pine bark.
Seth asks: ..... can you confirm that in fact gritty mix is perfectly fine used in any situation you would otherwise recommend the 5:1:1? I think the gritty mix might be overkill for 1) plantings of annuals, 2) veggies other than perennial plantings, 3) naturally vigorous plants with root systems that grow so quickly they require repotting annually to keep them in top shape (hibiscus, datura, brugmansia, others. IOW, if they aren't going to be in the same soil for more than a year, and they aren't something special (sentimental value, expensive, hate wet feet), (my thought is) they can be grown in the 5:1:1 mix with little or no conspicuous difference in growth rate or vitality levels.
I grow all my woody material and all succulents in the gritty mix, which is pretty much all I grow any more. The gritty mix might also excel at keeping plants in shallow pots healthy.
If these pots are 12, 8, and 4" deep, and the soil in the pot supports 3" of perched water, the tall pot has 75% of the soil free of perched water at container capacity (see below), while the pot on the right has only 25%, and that's a problem.
I was considering transferring to a larger ceramic pot with it's roots in the gritty mix but using 5:1:1 around it to see if that helps. When you mix soil textures in the same container, it's difficult to keep the soil appropriately moist. Part of the soil column can be too dry while the rest might be too wet.
I counted the number of Ficus I have in pots and came up with 45, not counting the propagules I start out of compulsion. They are all in the gritty mix and all doing very well. I think we could figure out what's wrong if you want to try. I know for sure it's hard to beat a properly made gritty mix for woody plants.
Can you see an advantage of using a gritty mix if I keep the hole small considering they're bare root trees? None - I would try to talk you out of it unless your soil is sand or sandy loam, then it won't matter as much. Anything else will collect water in the large spaces between the gritty mix particles. It's best to use native soil to backfill the planting hole. If the bare-root plants are really small, you might grow them out in a flat or individual containers for a year so you can plant out in early spring while they are still dormant - or, you could plant out this fall. Just try to avoid planting out in full sun, even if the plants are still dormant, especially if it is already hot where you live. We've been in the upper 70s and 80s all week. Don't know about where you live, but it's a consideration.
BTW - thanks for the kind words.
Al
chamaegardener (Z5) Northeast Illinois
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