When should I plant roses in northern California?

In northern California, and with respect to bare-root roses, the best time to plant is in either January or in February. 

For container-grown roses (roses that are already established in containers when purchased) the best time to plant in northern California (or anywhere for that matter) is throughout the growing season.

It’s best to plant container-grown roses not too late in the growing season. You’ll want your roses to get established before the first frost, which in northern California will be around mid-November. 

So, ideally, you’ll want to plant container-grown roses by around early September, if not a little sooner.