Agreed with Nhu on pumice, it has been a staple ingredient for my plants for years. However, I ran into some problems with the finer grade (Dry-stall) after using it over 1-2 seasons on a wide range of plants. The particles are finer, something like Grape Nuts cereal, and in combination with the 'fines' that are always present they formed a dense mass that was less aerated than what some of my bulbs wanted. This is in contrast to "regular" pumice with particles about 3x larger, which has never presented such problems. Some finer-rooted bulbs (Lachenalia, etc.) grew well with Dry-stall while others did not. Structurally, the key to a suitable mix is to have particles of different sizes that come together after a few waterings to provide space for air and roots and also provide a natural firmness. Soil firmness is often overlooked and is very important in keeping roots happy. Potting and watering techniques are important also, but finding the right combination of-- in my case-- pumice, sometimes perlite, sand and organics is critical to success in terms of physical structure. Dyla Hannon >