To build on Bob's comment about aeration, think again about the way Leo is growing his bulbs: in pure coarse sharp sand kept constantly damp. In those conditions I bet the roots are always moist but also always have a good supply of air (because there are pores between the grains of sand, where air can penetrate). So Makiko, I know it sounds like you're getting conflicting advice, but actually you're not. The key is to use a combination of soil and watering that keeps the roots damp, but allows good flow of air through the soil. Anyway, that's what I think. Hope that helps, Mike San Jose, CA