Hi Jane: I used gypsum in my yard in San Francisco with good results, but you do have to dig it in. I used a mushroom compost mix with absolutely disastrous results on some of my bulbs (in other words, they died). I am told mushroom compost is very high in accumulated salts from the fertilizer they use, as well as being alkaline. They throw it away because it can't be used for growing any more. I would NEVER use it again on anything at all. A local native plant nursery used the same mix and lost all of their plantings of some native plants. Diana Telos Rare Bulbs