Hypericums are shrubs that bloom on new growth, so pruning them actually encourages the plants to give you more of their lovely yellow flowers this summer. Although there are many varieties of hypericum -- also known as St John's Wort -- they are all generally hardy in the UK. Prune hypericum in early spring.
Inspect the stems for signs of winter damage and cut off any that you find. Cut them back to a main branch.
Prune off shoots that have bloomed, as they will not bloom again. Cut these back to where they meet a main branch.
Cut the entire shrub to within 2.5 to 5 cm (1 to 2 inches) of the ground. It may seem severe, but the shrub will quickly grow back, with more blooming stems than it had previously.
Rake up all pruning debris from around the hypericum, bag it and dispose of it.
Add a fresh layer of mulch to the soil beneath the hypericum and spread it out the same width as the shrub. Keep the mulch 7.5 cm (3 inches) away from the base of the shrub.
Water the hypericum as you normally do.