Interesting post. Thanks Some additional thoughts as they relate to SWCs. Would the water holding porosity be a good indication of the mixes wicking ability? If so then by testing the porosity, both aeration and water-holding, you could determine whether your mix will work in a bottom fed self-watering container. If you know for instance your tomato will drink 3 gallons/day in August. How could one translate water-holding porosity to wicking rates? Now I'm encouraged to mix up some of the mix I'm using this year and test it out. Then at the end of the season test out the used mix and see the difference. Then determine whether the mix would last one more year (for veggies). Wouldn't it be great if you could just get rid of the soil and just have air and water -- oh that's aeroponics, another set of totally different challenges/possibilities. Cheers

The finest-ground and thus for this purpose most useful ground bark is labeled "soil conditioner" at the garden centers. Here it is a bit less than $3 per 2-cubic-foot bag. I'll bet I have used 100 bags in the past several years and have seen no apparent problems.

Hi Laura: As Jacqueline, Tessie, and JeriJen often said: "location, location ...." Tapla's recipe of 5 parts fine mulch, 1 part peat moss, 1 part perlite is best for climate like mine: low-sun, flash flood warning and fast drainage is a must. It is recommended by Douglas Green, an owner of a large Ontario nursery of many plants in pots, including roses. If I use Al's 5-1-1, there is no need to put loose gravels or bark nuggets at the bottom for fast drainage. However, I use super-slow draining MiracleGro in green bag, and medium-slow draining Organic MiracleGro. I skipped this important process of putting loose stuff at the bottom, and regret it terribly. Now I have to dump the soil out of each pot, and start all over. I realize this after a heavy-rain simulation with a hose, with the pot flooding over and loses 1" of soil - which happens every time it rains here! Sure, Field Roebuck said it's not important, just put a paper towel at the bottom of the pot, and fill up with soil. His Texas climate doesn't have the low-sun, and 6" of rain flash flood. Each region should have its own recipe of best potting soil. Now I realize that the regular MiracleGro potting soil (green bag) might have been made for indoor pots, where one puts 1 measly cup of water per week. It's not meant for several outdoor heavy thunderstorms with 4 to 6" of rain per bout like my climate.

morpheuspa: I asked to get clarification from somebody was, well, not you (I threw you two red herrings in my latest post; you found one, you didn't find the other and it was pretty blatant. When I sent your reply off to a friend of mine who's a physics professor, he had some rather unkind things to say that I didn't, of course, post because I'm not some other posters around here. I have no idea what you are talking about. morpheuspa: When I sent your reply off to a friend of mine who's a physics professor, he had some rather unkind things to say that I didn't, of course, post because I'm not some other posters around here. Please do not hold back. I want to see a nasty response from a Physics professor. If you have the courage please name him and his university too. You know full disclosure is important. morpheuspa: To me, it's increasingly clear that you are still confused about the water retention curves above and what they mean. Remember, that's also a force retaining the water in the soil. Of course, there is a force retaining the water in the soil. That is the whole point here. If you water a medium to complete saturation to the top and let it drain and let it come to equilibrium then you will have two zones in the soil. A lower zone that is completely saturated - a zone where all air space is filled with water. And an upper zone that is not 100% saturated. The boundary is the )Kpa tension. The height of this boundary is the height of PWT. If undisturbed then this saturated zone will remain saturated for ever. Above this zone water is still present within the particles and as a film surrounding the particles. But it is not 100% saturated - meaning there is some air space also between the particles. As go up towards the surface the film of water keeps reducing and air space keeps increasing. This is what is captured in the water release curves. Depending how tightly soil particles hold on to water, the release curves are different. Peat has a higher affinity for water and so a larger (taller really) zone above the PWT that can hold substantial water but not fully saturated. Bark on the other hand has a lesser affinity for water so holds much less water at the surface and rapidly comes close to being dry as move up from the 0Kpa boundary. Water release curves, in short, describe how easy or difficult it is to extract that water from the soil particles. Below the 0Kpa boundary there is a lot of free water (unbound and bound) and above it is only bound water. Adding a wick to the bottom of the pot moves the bottom soil/air boundary lower. Water above the wick is under positive pressure to move away from the soil. The wick extends the soil bottom boundary causing a reduction in pressure in the water column above. Thus it moves the 0Kpa boundary lower. If the wick is long enough this boundary can be moved below the pot. Thus effectively removing the saturated zone in the soil medium. The water release curves do not directly address this but does so indirectly. The key is that the wick extends the bottom boundary to a lower point. Many of the subtleties of what I am saying has been presented by Dale in this thread with good diagrams and explanations. I encourage you to go through them again. I welcome and encourage you to send this entire thread including my explanation to your Physics professor friend. In many threads you have boasted about your scientific prowess. I do not doubt that. I tend not to do that but instead try to explain the best I can. But do not under estimate my background. So keep it to logical explanations and if I am wrong I will gladly admit it.