Just a side note of information - our temperatures are not dropping below 30. Last night 36, tonight will be 39. So, again, not really freezing the trees, but frost for sure! :)

Once established, the trees should be fine.

While small, you can make simple covers for them.

My trees are still uncovered, but I've pulled them under my deck for the night.
We've been dropping to 30F each night, with a few nights of 27F.

Josh

I once lived in a similar night time climate elsewhere in CA. Frost some/many nights into as late as April. It seldom dropped below 28F. There was little to no damage on citrus.

But if you are concerned with small trees you could cover them with light to medium weight frost blanket. It could stay in place all winter as long as it doesn't exclude more than 50% light.

Basically if your trees aren't growing in winter they will be OK. So don't push new growth with fertilizer or excess water late into fall.