At this point, I feel like I almost have to try a sand bed, just to see what'll happen. Will the roots grow throughout the sand, dive down into the clay, or descend to the top of the clay and then spread horizontally? Only if they have a death wish. (A lot of plants seem to.) Plants adapted to growing in coarse, highly-oxygenated soils would have no reason to try sending roots into a heavier soil. They would suffocate. I made the raised beds here in order to grow a variety of plants naturally adapted to coarser soils; the clay here (which is subsoil trucked in from some other place, like hell) has the consistency of frozen ice cream when wet. Plants growing in the clay do have an opportunity to send their roots down to the native soil, which is decomposed sandstone, before they're asphyxiated by the clay above the native soil. Doesn't always work. (Unlike most gardeners, I have little interest in growing plants not suited to my rainfall. A large number of summer-rainfall South Africans are perfectly hardy here; nerines, gladiolus, crocosmias, eucomis, etc., but they require so much irrigation in summer I would have to hire an assistant to water them every day. Or invest in an irrigation system.) Matching the plant to the soil is always a good idea. This is true with rainfall patterns as well. If you were growing a lot of Cape bulbs in a soil very similar to that of the native habitat, you probably wouldn't have to do anything, except maybe gloat. I suspect that information on habitat soils is readily available. (If you come across the word "drainage" in reference to a habitat soil, what is really meant is "highly oxygenated".) Bob Nold Denver, Colorado, USA 16 percent humidity ....a little high for me