[agavemonger]

I have to agree with you on the calcium part Matt. Most agaves prefer a higher calcium level in the soil. Amending with calcium at different concentrations would make for a most interesting study. Perhaps at certain levels we could obtain cross-banding and pink coloration in plants such as A.colorata, A. marmorata and A. zebra. It would also be fun to tinker with different formulations of fertilizer in different concentration levels of Nitrogen, Potassium, Phosphorus. I find that in outdoor growing that the 20-20-20 combination gives the maximum balanced concentration possible for a general purpose fertilizer that can be used safely on all plants save for acid lovers. I prefer liquid feed because there is no need to worry about overfertilization due to pelletized fertilizer buildup in the soil. You cannot leach out pelletized fertilizer, so there is the ongoing problem of fertilizer buildup and resulting high toxicity levels. The only way to leach out pelletized fertilizers is by completely repotting the plant in new soil. Certainly a scientifically controlled blind-testing would offer most interesting results on these plants. However, most afficianados simply don't have the number of plants necessary to undergo these type of studies. In the meantime, I'm finding that soils with high organic levels tend to balance out most conditions that would normally be detrimental as far as toxicity. These organically amended soils have a myriad array of biological checks and balances and constantly are adding plant-usable trace elements, hormones, complex vitamin trains, etc, as well as the more generic fertilizer constituants to boot. Very controlled amounts of supplemental "chemical" fertilizer at low concentrations in soluble form is very helpful and aid the plant in building up resistance to the plethora of bacteria, viruses and other bad guys inherrent in organic soils. Greenhouse growing exacerbates the bad effects of these little monsters, sometimes horrifically fast. Phytophora, Rhizoctonia, spider mites, etc., can all literally explode in growth in a greenhouse environment, so I advocate sterile, soil-less growing with pasteurized potting mixes for the high heat and humidities inherrent in a greenhouse environment. Certainly a large part of the joy in growing rare plants in a unique garden setting is the constant fun with "experimenting". But when it comes to fertilizers one must be extremely cautious not to overdo it. It is all to easy to ascribe a plants renewed vigor to the trace element, hormone, or vitamin you just overdosed it with; this is very seldom a logical conclusion and is usually due to other factors such as the onset of spring, a lower toxicity level due to rainwater leeching, a better concentration of auxins in the nuclear makeup or what-have-you. Without large blind-testing experimentation most conclusions reached are really only assumptions and we all know what a little hyphenation can do to assume. An amateur would be far better off by concentrating on efforts to improve water quality by investing in rain-water capturing efforts or water purification technologies. When used with pure water, fertilizer concentrations can be doubled as compared with our standard, salty, Southern California water which generally measures out at .5 -.8 mmhos. This is roughly half the maximum allowable concentration of salt that most plants can tolerate without root damage. It's a wonder our plants don't drop dead from heart attacks! Happy growing! the monger