Hypericum prolificum, or shrubby St. John's wort, is a medium-sized shrub with minimal maintenance needs. It does, however, warrant pruning annually in the spring. If left to its own devices, the shrub may reach 4 feet or more in height. Unless you want a small tree on your hands, it must be cut back annually. Pruning is also a way to clean Hypericum prolificum, which means getting rid of any old, dead or diseased tissue that may otherwise lead to fungal growth and other infections.
Cut Hypericum prolificum's overgrown stems back to just a little shorter (no more than an inch or two) than the height and width you want the shrub to reach. Use a pair of sharp bypass pruning shears. Cut at a 45-degree angle, just above the nearest bud or node, which is the swollen bump on the branch that will grow into new plant material.
Remove any dead branches. If a branch is dead, it is likely brittle, may snap if you attempt to bend it slightly and will not have produced any growth last season. Prune dead branches with your pruning shears, back to their point of origin.
Prune diseased branches as soon as you notice them. Do not wait until spring. Diseased branches may have soft spots or fungal or other abnormal growth. Prune behind diseased portions, 2 inches into healthy plant tissue. Discard pruned material far away from the Hypericum.