I'd like to endorse the entire text of Ken's last thoughtful and scientifically sound comments. and they deserve to be promulgated widely. The soilless mix ideas, (as I remember), can be traced back to University of California at Davis experiments on seed germination and control of disease in greenhousesand hydroponics back in the 30s and 40s. I would add only: Learn about the provenance of the plants you want to grow. If the plant is found in clay, or rocky clay, do not put it in a "nice bed" of enriched peat and fertilizer to give it what the "poor thing" lacked in nature--you are thereby likely to make it "go to sleep in its bed" forever. If it grows in scree--make a scree before you try to grow it. At least try to approximate similar conditions. Can't get serpentine? Try decomposed granite. Add a handful of Epsom salts to your broken concrete and sand mix. Also, re woodland plants, if the plant is known to grow in deep shade--be aware that it may well have germinated and grown in shade long before the trees became a dense canopy above it. I am finding that most arisaemas can take about twice the amount of sun that one might expect, given adequate moisture and either sharp drainage through porous soil, or clay (depending on the species) where moisture content is limited by water's draining off the surface because the surface is slanted. Cheers from Glenview, IL where the snow is melting and the high will be 44° F.