When to prune: around the end of winter or at the beginning of spring.
Simply keep an eye out for the first set of plump new buds, and when you find them, trim the stem so that it is just above the new growth.
If you have a vigorous plant and you want to keep it confined, you may trim it back severely — almost all the way to the ground — in the late winter, before the new growth begins.
This will allow you to restrict the plant from becoming out of hand.