Fifteen distinctive dahlia forms are recognized by the American Dahlia Society. They are determined by the shape of the petals. Formal decorative denotes the archly symmetrical. Cactus varieties spike out like sparklers. Anemones have an orderly frame of tame petals surrounding a frizzy center.
Pompons look just like colored golf balls perched upon green tees.
Only blue continues to elude centuries of diligent hybridizers. Dahlias love the Bay Area climate, growing well as long as there is at least half a day of sun. To plant, dig a hole six inches deep, pound in a steak, place the tuber eye up, and cover with three inches of soil. Do not water until the green shoots are well above the rim of the hole. Gradually fill in the hole with more soil.