I'm still looking for pumice, as well as unadulterated bird grit, but I have used both foam peanuts and large solid pieces of foam in the bottom of pots to reduce weight and save potting soil. An additional disadvantage to foam peanuts is that roots grow through and into them, making it difficult to repot the plant without breaking roots. The jury is still out on the larger pieces of foam but I like being able to move large pots by myself. Kathy Stokmanis Northern California, zone 8 or 9, Eranthis, Narcissus, Iris reticulata and Crocus are starting to bloom.