|How do you start yams? What is the typical yam growing season? Will they grow well over the southern California winter?
|I'm afraid your mild summers won't suit sweet potatoes. You can give it a try, though, by purchasing one at the store and cutting off both ends. Prop the ends up in a tray of water and they'll grow roots and sprout vines.
Transplant into regular potting mix in a container, or try planting it directly in the garden in the sunniest spot possible. It may or may not produce tubers, but at least you've had the opportunity to try! You can increase its chances by using black plastic mulch on the soil, and placing a reflective surface behind the vines to maximize the effects of the sun. Good luck!