The best time to prune this way is late winter or early in the spring when the plants are still dormant. Although this style of pruning can be carried out every year it is best to do it every other year so that you don't exhaust the plant.

Can I cut back Hypericum in autumn?

Hypericum Hidcote flowers on stems which have not produced buds in the current year and the standard advice is to prune it in early spring, some time in March. ... However, we always prune ours in late summer to early autumn when the flowers are no longer being produced.

When should I cut back Hypericum?

It is not essential to prune Hypericum but if pruning is needed spring is the time to take the shears to it. A light prune in early spring if you want to restrict size or tidy up. Some Hypericum are prone to rust and pruning in the spring is one way to remove rust tainted branches.