Sweet potatoes are perrennials in the tropics. For most of us, we grow as annuals, dig them in fall cure and store. Have choice roots sprouted in spring, and the little plants transplanted to the field or garden. They may overwinter in Southern Cal, but they would get so crowded they probably would not produce much.

How cold has it gotten? Sweet potatoes are very sensitive to the cold. You should also check the size of the potatoes. It might be time to dig them up.

They would do better planted in late spring or early summer (around may or June), I think August is too late. They like warm weather. They should be harvested in the fall after the first frost or when the vines start to die. Don't forget to cure them before cooking with them.