Welcome Luis, First, I commend you for starting your planning in March for growing next Fall. I wish I had such foresight when I began. Having everything in pots can be an advantage. Many on this list grow primarily in pots. It looks like you have done some research already, as you knew to tell us where you live (coastal California), and you recognize the type of bulb grown (winter growing) affects choice of potting mix. (The book 'Grow Bulbs' by G. Duncan says winter growing bulbs have lower nutrient needs.) I am experimenting with several recipes for potting mix but it is too soon to know which works best. I got started by reading this page: http://pacificbulbsociety.org/pbswiki/index.php/… As Kathleen mentioned, searching the archives can dig up a lot of information. The equivalent to typing "potting mix" in the search box is this google search: "potting mix" site:///http://www.pacificbulbsociety.org which finds 604 results! You see PBS members do write often on this important topic. Jane is an expert and I take notes whenever she writes. But given my limited skills I cannot grow a Lily in the same potting mix as a Lachenalia. (The Lily needs more nutrients and water whereas the Lachenalia would rot in a mix that takes half the summer to dry out.) It may be a matter of scale. My garden is small and I spend a lot of time with each plant. If I were a real "grower" on a large scale it would be too complicated to adjust soil, type of pot, feeding and watering to each species. The general advice I read is "you can easily add water but it is difficult to remove water." (I forgot the source.) That is one of the ideas of a rapid-draining, porous potting mix. Today it is raining, so everything gets watered, whether or not the leaves have begun to turn brown (a signal to cease irrigation). The plan is for the bulbs which need a dry dormancy to be in a soil that drains and dries. Thanks for the Lachenalia sand tip Dell. I'll try that, as soon as I get replacements for my lovely Lachenalia that rotted because I had not realized how a mix with too much coir takes months to dry out here. - Gastil Coastal California