Hi Mike, If the soil is on the heavy side like the clayish soils I have here in NY, I found road sand tends to help it to dry out and drain better. Don't know how readily available this is in Cali, its the stuff they use on the roads in winter here, minus the salt. It is smaller than gravel but bigger than beach sand, and not uniform in size, which is good. Its kind of like granite grit but mostly smaller. Of course the Cape bulbs themselves have preferences for different soils in habitat, some grow in clay that gets wet during winter while others grow in very sandy soils and since your climate roughly mimics the winter rainfall Cape region, species preferences might matter too. Organics like composted leaves will hold moisture better if you have sandy soil, but you will as you said lose it over time if its not replenished. I'm sure some of the tougher stuff would survive in whatever soil you have though. Ernie Briarcliff Manor NY Z7ish, galtonias are spiking, Tritonia disticha, Albuca shawii, Gladiolus Ruby Papilio, are blooming in the gardens, lots of summer oxalis and other stuff in pots also blooming