In Santa Monica we are blessed with at least a 10 month growing season, more probably year round. Even so, some crops just won't make it through the short days of winter. They sense the sun receding and shut down. From about the middle of December to the middle of February it is hard to coax production out a garden even here in sunny Santa Monica.
The crops that do best through the winter are typical cold or cool weather crops. Radishes, lettuces, carrots, turnips, broccoli, cabbage, peas, spinach, chard, etc. Some of these such as radishes, turnips, lettuce and peas are relatively easy to grow. The others are somewhat more difficult to coax along even in our near perfect climate. If you have citrus trees you will find those most productive during winter months. I am trying an experiment with some Kentucky Wonder pole beans, but I won't demand that it work out well since beans need long days of sunshine to mature and fruit. I was told, however, that some varieties can be tricked into producing by the scattered, around the clock, ambient light of the urban environment. We'll see and I'll let you know later.
One problem I have had with cool weather crops is that sometimes the weather in Santa Monica doesn't realize that it's fall or even winter. I have had more than one crop of peas ruined by a string of 80+ degree days late in October. Sometimes it seems like it is cooler here in July than it is in the fall.
A nice aspect to the fall garden in Southern California is rain, like the inch or so we had today. From mid-April or so right on through September rain is almost unheard of here in the southwestern desert. But with the shorter days comes natural irrigation that more gently and evenly soaks the soil and provides much needed moisture to the roots of our plants.
Meanwhile, my summer tomatoes are still producing and the fruits continue to ripen. We may enjoy another month or so homegrown tomatoes before we have to give up on them.
Don't let the shortening days get you down. There is still plenty of produce to be grown right on through the winter in our ideal climate here in Santa Monica. As I suggested earlier, keep on spreading the seed and see what works for you on your soil. Then come back and share it with us so that we can all benefit from your experience.