As a rule of thumb, your hypericum plant should be pruned in March to mid-April, as needed. You wouldn't want to wait too long or you will run the risk of cutting off the flower buds, consequently missing out on spring blooms. It's a compact plant and probably won't need pruning at all. However, if a broken branch is driving you crazy, there's no harm in snipping it off any time of the year. Be sure to enjoy some cut branches of berries in the fall; they will last over a week when placed in a vase.