I have found that each ingredient used in a more gritty medium retains a different or slightly different amount of moisture, depending on various factors. Numbers are not my thing, so without bringing math or percentages into the discussion, I begin by soaking the pine bark fines, akadama, or any other moisture retentive ingredient I'm using overnight in a covered container before mixing my medium. I then get rid of any extra water that hasn't soaked in. For all intents and purposes, the coarse perlite I use doesn't retain enough moisture to make note of, in my opinion. But beginning with moistened pine bark and akadama, I can ensure that the roots of any freshly potted plants will not dry out too quickly, but also won't have too much moisture to deal with. When I water, especially when using the addition of fertilizer, I use deep saucers to catch the excess, then reuse that a second time to make sure the plant has been adequately watered. Once I'm sure the plant is sufficiently watered, I dump the saucers. I never want to leave them soaking when the process is done. Using a more porous mix means watching moisture content more closely, and most likely watering more often than if one were to use what passes as potting soil sold in bags. But the extra effort is very worth it! I continually read tags, instructions, and hear people say things like "water once a week" or things of a similar nature... when the truth is, I only water my plants as they need it. I only drink liquids when I'm thirsty... why would a plant be much different? :-) There are many substitutions as ingredients go... turface, cherry stone, lava rock, perlite, pine bark, akadama, etc... some can retain moisture, others not... and at differing rates. I sort of tailor make my medium based on factors such as pot and plant size, plant type and needs, the climate or micro-environment it will be kept in, etc. Happy Gardening!

To be honest, I have some measure of curiosity about what you discover, but I don't know how applicable the information will be to the soils others might make (because of variability). As you can see, I use screened Turface and pre-screened granite, along with pre-screened fir bark to make my soils, so I can almost perfectly replicate the basic soils from batch to batch - all my variables are insignificant. Most of those making the soil will be using unscreened Turface and bark. The fines included in either/both will often substantially impact porosity and increase water retention. In practicality and in most cases, I would expect the figures describing total porosity and air porosity at container capacity to cover a fairly wide range, depending on what others used to make the soil, from person to person and even batch to batch by the same person. Of course, any graph of the water retention curve would reflect this variation from soil to soil as well. Part of the reason I would be a little less interested in the hard data than I would be in your empirical assessment(s), is that the soil is formulated with a focus on plenteous aeration, which we know has an inverse relationship w/water retention. It takes advantage of particles, the size of which are at or just under the size that would guarantee the soil retains no perched water. It's not a soil for the indifferent, who wish for long irrigation intervals; it's a soil for those willing to put forth a little extra effort - first to make the soil, then, to water a little more often. I suppose I might have shortened my reply by saying: IOW - grow in it too - don't just test it - and tell me/us what you think. ;o) Take care. Al

The post you linked to that had the recipe for gritty mix with vermiculite was for someone growing in the hot windy desert. I'd skip the vermiculite and play with the screened Tureface:grit ratio to up water retention. Freezing Commonly, each species of plant has a general range of cold-hardiness. Within species and cultivar, cold-hardiness is genetically determined. That is to say that a plant that is propagated from cuttings or tissue culture will have the same ability to resist cold as the parent plant. Plants cannot "develop" a greater degree of cold-hardiness by repeated or prolonged exposure to cold, even after 100 years (trees). If we pick any plant at random, it may or may not be able to withstand freezing temperatures. The determining factor is the plants ability to prevent freezing of bound water. Bound water is the water inside of cells. There are actually three kinds of water to consider when we discuss "freezing". The water held in soil - When this water freezes, and it can freeze the soil mass solid, it doesn't necessarily kill the plant or tissues. Then there is free or unbound water, also called inter-cellular water. This is water that is found in plant tissues, but is outside of living cells cells. This water can also freeze solid and not kill the plant. The final type of water is bound water or intra-cellular water. If temperatures drop low enough to freeze this water, the cell/tissue/plant dies. This is the freeze damage that kills plants. Fortunately, nature has an antifreeze. Even though temperatures drop well below freezing, all plants don't die. In hardy plants, physiological changes occur as temperatures drop. The plant moves solutes (sugars, salts, starches) into cells and moves water out of cells to inter-cellular spaces in tissues. These solutes act as antifreeze, allowing water in cells to remain liquid to sometimes extremely low temperatures. The above is a description of super-cooling in plants. Some plants even take advantage of another process to withstand very low temps called intra-cellular dehydration. The roots of your trees can stay frozen for extended periods or go through multiple freeze/thaw cycles w/o damage, so long as the temperature does not fall below that required to freeze intra-cellular water. If roots remain frozen, but temperatures remain above killing lows, dessication is the primary concern. If the tree is able to take up water, but temperatures are too low for the tree to grow and make food, stored energy becomes the critical issue. Dormant and quiescent trees are still using energy from their reserves (like a drain on a battery). If those reserves are depleted before the tree can produce photosynthesizing mass, the organism dies. There are a number of factors that have some affect on the cold-hardiness of individual plants, some of which are length of exposure to seasonal cold, water availability (drought stressed plants are more cold tolerant), how recently planted/repotted, etc No one can give a definitive answer that even comes close to accurately assessing the temperature at which bound water will freeze that covers the whole species. Unbound water is of little concern & will usually freeze somewhere around 28*. Some material will be able to withstand little cold & roots could freeze/die at (actual) root temperatures as warm as 25-27*. Other plants may tolerate much colder actual root temperatures - as low as 10*. There's just no way of knowing unless you have a feeling for how cold-tolerant the genetic material the plant was derived from might be, and finding out is expensive (from the plant's perspective). ;o) Another example of this genetic variance is that trees found growing and fruiting well closer to the equator need no chill time, while other trees, derived of genetic stock from a more northerly provenance may need a period of chill to grow with optimum vitality in the subsequent growth period/cycle. It's wise to remember that root death isn't instantaneous at one particular temperature. Roots succumb to cold over a range of chill with cultural conditions affecting the process. The finest roots will die first, and the slightly thicker and more lignified roots will follow, with the last of the roots to succumb being the more perennial and thickest roots. Since any root death is a setback from an energy allocation perspective, and root regeneration takes valuable time, it's probably best to keep actual root temperatures in the 25-40* range as long as we can when the tree is resting, even though the organism as a whole could tolerate much lower temperatures. Even well established trees become very much like cuttings if all but the roots essential to keep the tree viable are lost to cold. Regeneration of roots is an expensive energy outlay and causes the trees to leaf out later than they normally would and shortens the natural growth period and reduces the potential increase in biomass for the next growth cycle and perhaps beyond. And We know that when trees are exposed to freezing, the finest hair roots - the ones that do the lions share of the work are the first to die. In many woody plants, these roots begin to die as soil temperatures drop below 30-32*. As temperatures drop further, larger and larger roots succumb to killing low temperatures. The point is - that many trees that SURVIVE are left with only the largest roots to support them because much of the rootage has frozen. These trees are slow to respond in the spring because they need to utilize stored energy to regenerate lost rootage before they can move sufficient water and the nutrients dissolved in water to support either growth or the flush of foliage that makes the food that allows the tree to grow (this, in the case of deciduous material). So, while trees might survive exposure to borderline killing low temperatures unprotected, we KNOW it is better for the tree, especially from an energy management perspective, if we give them protection that ensures actual root temperatures don't drop low enough to kill even the finest roots. For most temperate trees, that means we should strive to keep low root temperatures in the upper 20s at their lowest, and below 42* to keep them from growing until spring when we can get them into good light w/o worrying about frost/freeze. Al

Sure! I can certainly post back once I have some results to report. I have a tendency to dive much deeper than necessary into details of any hobby I take on...in the end I'm sure a lot of these details aren't critical. I'm in a detail-oriented profession so I think it's just a natural mindset for me to fall into. In this case though, the more I think about the whole coco media buffering, the more I realize that most people who have to worry about it are growing in 100% coco-based media or are utilizing hydroponics. Any of the negative effects I would experience from unbuffered coco (if there would actually be any such negative effect in practice) should be largely offset by the fact that the coco is only 1/3 of my mix. Also I'm applying a fertilizer with every watering that has calcium and magnesium in it so the cation exchange issue should theoretically only be temporary as the media should balance over time. Some of the research I've read indicates that it is more important for the coco to be properly washed to a low electrical conductivity than it is for the cation exchange complex to be buffered. This is because seedlings and young plants are substantially more sensitive to the negative effects of high sodium exposure than they are to a temporary deficient quantity of available calcium/magnesium. The good news is that most of the high quality sources of coco products are washed to a very low electrical conductivity, it's just hit or miss whether a particular manufacturer buffers or not. Since I'm going to be growing a few plants each of some of my aji limon peppers and purple jalapenos, I think I might try buffering some coco and not buffering the other coco and see if there is a noticeable performance difference between the two if the rest of the mix is the same. It would obviously only be anecdotal, but it would still be an interesting thing to see!