Prune it anytime it is actively growing, and it usually looks best with a heavy pruning right at the beginning of thegrowing season--take it right down to stubs. Midseason pruning should be more artistic, pruning the longest limbs back to side branches, or to sideways facing leaves. Always leave some growing tips intact, since new growth is where the flowers form. Don't prune too close to fall--like now--since that will make it harder to overwinter, unless you are taking it into a heated greenhouse.