Agreed with Michael's comments here, especially particle sizes. The "magic" formula always has the right proportion of particle sizes and proportion of organic to inorganic materials. I mix small batches by hand and so there are inconsistencies but these allow observations of what works over a wide range of plants. Uniformity, like efficiency, should not overshadow other important considerations. I would add that a major factor is the watering habits of the grower. I know extremely good cactus growers whose mix may be fine and silty (with bottom tray watering) or only pure, coarse pumice (particles about 7-12mm diam). For the former grower the soil becomes *very* dry between waterings while the latter, owing to vagaries of nursery staff, are watered regularly, to an extent that would induce many fatalities for most other growers. Both of these growers are in an ideal cactus growing climate. Mixes with significant % of fines should be allowed to dry more thoroughly between waterings and if carefully managed this can be a real advantage-- less labor watering. I have recently grown fond of a product called "play sand" that is quite fine (around grade 25-30) but very clean. It looks like silica sand but (one hopes) without the particulate hazards. Mixed with 2/3 or more pumice and some organics it looks like it may be a good fit for many of my plants. What goes on during dormancy is important also. I find sand to be a good insulator for dormant bulbs and those with live roots go unwatered for 4-5 months minimum, with plenty of hot daytime temps. In a too coarse mix they would suffer desiccation at the roots, unless the roots are very thick. This brings up a final point: fine textured mixes are better suited to plants with fine roots (e.g., Crassulaceae, mesembs, some irids). Coarse mixes with more large particles (and some fines!) bring better results for amaryllids. Dylan * *