Last year I planted crimson clover and had great success plus beautiful flowers. It attracted so many lady bugs and bee's it was amazing. I don't use pesticides so any beneficial bug was welcomed with open arms.
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I did it one year, but had trouble getting the stuff to decompose. It took so long I lost a growing season. So warm/dry here, things don't rot as fast as in more extreme parts of the country. Now I just add compost and let it sit for a couple of months.

I don't know whether it would work in your area but here in Bakersfield they plant alfalfa in the fields as a cover crop.

Here is a link that might be useful: My pond

I used all sorts of things for cover crops when I had a big vegetable garden on Point Loma. Right now, you are a little limited by the cold and what will germinate. I'd try barley or one of the other cereals, mustard family, favas or field peas. There's no reason why you can't plant a mixture. The grasses will give twining legumes some support. Peaceful Valley sells a big selection. For small amounts of less expensive cover crop seed, I'm fond of cruising the bulk bins at Whole Foods, too. In the warm weather, buckwheat is your very best friend.

Go ahead and plant something. Even if growth is limited, it will do your soil some good. I've never had trouble with turning anything under.

Thanks for the tips everyone. Todancewithwolves, that pic is amazing. I'm thinking about growing that stuff just for the show. That looks great.

I just ordered some barley/mustard concoction from Peaceful Valley. I guess I'll see what happens with it. It should be an interesting experiment.

My next question is about turning it under. Assuming I get the stuff planted shortly, I'd like to turn it under around Mar 1 because I usually plant my summer stuff around the 20th of March. Obviously, it probably won't decompose in three weeks. When I'm preparing my beds in early March, do I need to add a lot more nitrogen to the soil to compensate for the decomposition?

No, just turn it under. No need for nitrogen, it will be fine.

I mowed mine as the flowers died and tilled it into the ground in April. I added the clipping to the compost pile. I have no irrigation system and clover helped keep the ground moist. Clover and sweetpeas are one of the best plants in adding nitrogen's to the soil. I also had worms galore which helped loosen the soil.

Here's my sweetpeas in March.
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Edna

Just wanted to post an update and thank everyone for their responses. I took jxbrown's advice and planted barley. Despite the horribly cold conditions this Jan-Feb, it got to about 10" high before I took a weed whacker to it in mid-March after about two months of growing. It was also incredibly thick and lush. After I mowed, I turned it over.

While I'd been planning to put in my warm season stuff a couple of weeks ago, I've held off because of the wacky weather. However, they're going in the ground tomorrow. This afternoon, I did some more soil amending and digging and was absolutely floored by how well the barley had decomposed--it was nearly impossible to find.

Hopefully, it'll lead to great results this summer. Thanks again for the input.

That's great! Maybe I'll try barley. Thanks for the update.

I would be grateful to any SoCal gardener who is experienced enough to make a cover crop calendar for zone 9-10 here in SoCal.

Something like:
August - sow BUCKWHEAT - toss it under everything
September - turn BUCKWHEAT - sow x,y and z
November - turn....A ; Sow... B

There are some wonderful articles on cover crops out there, but I cannot imagine that the timing advice fits warm SoCal correctly.

Btw, those two gorgeous photos alone should be enough to encourage anyone thinking about cover crops to jump in and do it! Wow guys. Please post cover-crop-beauty-shots!

Here is a link that might be useful: Article: Use Cover Crops to Improve Soil (B. Pleasant/Mother Earth News)

This post was edited by babyg on Fri, Aug 15, 14 at 16:27

Oh... I also think this CHART is pretty phenomenal. It lists cover crops and their specific uses. The article I posted above is pretty detailed.
For example the Barbara Pleasant (Mother Earth) article linked above, she suggests "biodrilling" into clay soil with the sharp roots of daikon radishes and canola rape. Then you can turn to the chart I like here and find out that diakon attracts beneficial insects and loosens heavy soil, but it doesn't fix Nitrogen or add much organic matter. However, Canola will add organic matter, keep out weeds and tolerate the heavy soil. Used together its a pretty good pair, but still doesn't fix any Nitrogen.

I think these two resources together are great as tools for selecting the best cover crops (together with zone info, etc) but they don't give me a good idea of when to plant what in zone 10 California. Hence....I'm still begging for a good calender of which common cover crops can be planted/turned in which months.

I'd like to see: buckwheat, clover, barley, peas/beans, oats, radish (esp daikon), rape, rye, vetch.

Here is a link that might be useful: Cover Crop Chart - Functions of various plants