If your local rock dealer has a fairly inert rock source and if you don't mind the added potting soil weight I find that 1/4 minus gravel gives excellent results. It is cheap and if the fines bother you just run the gravel through a hardware cloth sieve. Here in the rainy Portland Area I find that a great mix for bulbs in pots is equal parts soil, the above gravel and coarse peat. Greig Warner Vancouver, WA