When it comes to root health, pots with gas permeable walls carry the day. Terra cotta clay pots are better than plastic or vitrified clay pots and fabric pots are better than terra cotta clay. The reason is greater gas exchange through container walls and the fact that an increase in gas exchange comes with an increase in evaporative water loss, which can be a lifesaver when using water retentive media. There will still be a PWT in these pots, and for any given medium it will the same ht in a pot with rigid sides as in the fabric or air pots at container capacity. Container capacity is a measure of how much water the grow medium in a pot or container holds at the moment it has stopped draining after having been watered to the point of complete saturation. The ht of the PWT and how long it affects root function is usually key/critical in determining what opportunity a plant will have to realize as much of its genetic potential as possible (within the limiting effects of other cultural influences). The factor that most affects the ht of a PWT is the size of the particles from which the medium is made. So, reducing the duration of PWTs limitations increases the opportunity for plants to realize a greater measure of their genetic potential. But wait! There's a more important consideration. If you place your fabric containers directly on the ground/soil, from the perspective of hydrology it changes the fabric container to a raised bed; this, because water is free to move through the fabric between the grow medium and the earth, with the earth acting as a giant wick. This means, because of the increase in the force of adhesion in the mineral soil beneath the pot (due to a mineral soils much larger o/a surface area on a per volume basis), water in the soil will be pulled downward with enough source to overcome the capillarity holding it perched in the container. As long as you don't place the fabric container on coarse sand, peastone, or other large particles, the earth will likely pull all perched water from most media one is likely to use in a container. I've mentioned this and the fact that healing in your pots situating them directly on top of soil turns them into raised beds. the only caveat being it's essential that there is a 'soil bridge' so there is continuity of the soil column between the soil (earth) and the grow medium in the container, through the drain hole(s), so water doesn't have to jump an air gap to exit the container. This applies more to pots with rigid walls and is not a factor when discussing fabric containers. Al

I was invited to discuss nutrient supplementation on another popular gardening forum very recently. The reply I left is rather appropriate to your wonderings, so I'll post what I left there: If what I leave you with finds you with additional questions - please ask. I get asked this question frequently, or a variation like: "I want to feed my plants the best - what's best & how often should I feed?". Most people queried, would look right past the question and hand you a box or direct you to the fertilizer section of a plant store for "plant food". Actually, you cannot feed your plants. Food provides energy - fertilizer does not. Plants manufacture their own food during the process of photosynthesis when the pigment chlorophyll traps the energy of the sun in a molecule of carbon dioxide and water. The result of this miraculous reaction, without which the earth would be uninhabitable, is a molecule of glucose - sugar - a carbohydrate - photosynthate. The molecule acts just like a battery, storing energy from the sun that can be translocated to all living plant parts for immediate use, or stored in living cells - roots, leaves, and cambium for later use. In order for a plant to make and use food efficiently, certain elements need to be available to the plant. In fertile garden soil, it is likely, even probable that that the nutrients will be available in a usable concentration. In container culture, it is a virtual certainty that we will have to accept the responsibility for providing nutrients in usable concentrations for the term of the planting if we are to expect plants to grow at or near their potential genetic vigor. The three main elements or compounds that are needed for plant metabolism are nitrates, phosphates, and potassium (NPK), and they represent the bulk of ingredients in balanced fertilizers. We term these ingredients macro-nutrients, sometimes referred to as "the majors". Also included in the macro-nutrient category, but necessary in lower concentrations are magnesium, calcium and sulfur. Rounding out the list of nutrients needed to keep plants healthy are the micro-nutrients, or "the minors". These nutrients include iron, boron, zinc, copper, manganese, molybdenum, chlorine, cobalt, and nickel. Please note that some of the minor elements, or micro-nutrients are required in such minute amounts that deficiencies are rare in garden soils, but more common in container media. For that reason, it is good practice to insure that you use a fertilizer that is complete, including the minors. If the minor nutrients are not listed on the fertilizer package, and youre unsure that your soil contains an adequate supply, an excellent way of providing the minors while furnishing major nutrients is to use a granular soluble or insoluble product (e.g, STEM or Micromax). Organic fish and/or seaweed emulsions as part of your supplementation program can also be effective, but here I'll concentrate on the major elements. Now that we've have seen that fertilizer is not plant food, but a way of delivering some of the raw materials or building blocks that plants need to make their own food and keep their systems orderly, I'll briefly say that it is important that we insure the soils we use contain adequate/appropriate volumes of air and water so as to make nutrient uptake possible and efficient, but that is another subject I won't dwell on today. You can probably use a schedule or timetable to fertilize plants & have them be reasonably happy, but I use a different approach. If you do choose to fertilize on a regular schedule, it makes no sense to continue to fertilize when plants are quiescent due to chill, heat, or other unfavorable cultural conditions, Under these conditions, you might extend the preset intervals. Plants need more nutrients when robust and actively growing and less when they are "coasting". I use a two-pronged approach to my fertilizing. The first thing I do is note leaf color of older leaves. N is a very mobile nutrient in plants. When it is deficient, plants "rob" it from older leaves to use in the production of new vegetative growth. So, when I see a lightening of leaves toward a lighter green or yellow, especially older leaves, and I'm sure that other cultural conditions are what the plant requires for good vitality, it indicates to me a need for supplemental nutrients. A simplification of how I fertilize is: I attempt to get a higher percentage of N to foliage plants or those that are being grown for a reason other than blooms or fruit. Highly nitrogenous fertilizers support the plant during the growth of leaves and foliage. For flowering/fruiting plants, the phosphatic portion of fertilizers aid flower/fruit production, so I'll usually include the intermittent use of a fertilizer with higher percentage of P. Potassic compounds (K) stimulate the growth of roots and are included in adequate percentage in all complete fertilizers I use. I use both chemical and organic fertilizers. As noted, but worth repeating, I determine the need for fertilization by leaf color. When leaves lighten and fertilizer is needed, I mix a recommended full strength solution of 20-20-20 soluble granular fertilizer and add a full strength solution of 5-1-1 fish emulsion in the same mix. This mix, I'll apply to foliage plants & plantings that are not dependent on blooms for their beauty. This is pretty much my standard for these plantings. For blooming plants, I'll use the same 20-20-20 fertilizer with a 2-3-1 fish emulsion included - UNLESS leaf color is good. If leaf color is good - I'll substitute a bloom-inducing, soluble formulation like 10-52-10 or 15-30-15 and still use the 2-3-1 emulsion. In all cases, I'll apply these solutions to well-hydrated plants growing in moist or damp soil, thoroughly saturating the entire volume of soil in the container. I prefer the reliability and immediate action of the chemical soluble fertilizers for results, but understand the wont of some to remain organic. Generally speaking, organic fertilizers do release nutrients over a fairly long period, but there is a potential and considerable drawback in depending solely on them. They may very well not release enough nutrients to give the plant what it needs, when it needs it for best vitality. Organic fertilizers depend on soil organisms to break them down into elements the plant can assimilate, so most of them are effective only when soil is moist and soil temperature is warm enough for the soil organisms to be active. This soil organism population is a boom/bust proposition in container soils due to the extreme variables of temperature, moisture and pH. Nutrients in chemical form are immediately available for plant use and exhibit no dependency on soil biotic activity for availability. Plants do not care whether their elemental building blocks are provided in chemical or organic form.color> Additionally, practices that promote high population numbers of soil organisms that feed on organic particulates hastens soil structural collapse, which is certainly counter-productive to your need for an extended-life soil. When I think of soils that must last long term, I immediately consider the percentages of organic:inorganic componants. If I want a soil to last several years, I'll use something with more than 2/3 inorganic parts, like Turface, pumice, perlite, Soil Perfector, etc., and only 1/10 - 1/3 organic parts - usually fir or pine bark. For plantings of 1-2 years, I'll use a mix of primarily bark, peat, perlite. Well, I certainly never intended to go on so long; and I know I bored some into leaving before they got this far, but for those that made it to the end, I hope my thoughts were clear enough to provide some insight. Al Fassezke

Not at all, and I don't remember writing anything that should leave anyone with that impression. If I had to identify the crux of the thread, it would be that to take advantage of highly aerated media and their sharp drainage, it's essential to start with a very large volume of coarse ingredients, and there should never be enough fine material to fill all the spaces between the large particles. When you add a marble/perlite) to a jar filled to the rim with sand or peat), aeration of the medium in the jar DECREASES, and continues to decrease as you add more marbles/perlite. It is only when you have added a volume of marbles/perlite) so large there is not enough sand/peat) to fill all the desirable pores between the large particles that aeration begins to INCREASE. This is called the "threshold proportion". Al

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