I think growing a canopy would be best. Shade covers dont work as well because they can get weighed down in rain or blown over in wind (and any foliage that they touch will be burned if there is a freeze). And with a natural canopy, you never have to worry about putting it up or down depending on the low temperature.
-Alex

Thanks Alex! Yeah I was thinking that too, thats why I was thinking of tilting it somewhat. But I need something that will keep temps up a quite a bit. I seen canopy keep bananas green even on cold years. So its probably best to go with what I know works. lol

- US_Marine

You're on the coast aren't you? What type of canopy would you grow? I'd probably try a fast growing Euc, (perhaps E. Ficifolia) or a Jacaranda Mimosifolia? My Jacaranda is usually evergreen except in really cold winters (and in early summer when they drop their leaves and bloom). Embothrium coccineum also comes to mind. These trees would add a tropical look to your landscape as well :)

Nope, central valley. I was thinking that anything that gets fairly tall and wide would work, as long as its evergreen, such as pines, live oaks and many others.

- US_Marine

I can tell you that the live oak is pretty effective from my experience here. In the front of my yard, I have no overhead canopy in the form of a tree. All the grass turned brown from a fairly mild frost that we had (31F), under the tree, all green, all year.