Hypericum, also known as Rose of Sharon and St John's wort, is an easy to grow summer flowering shrub grown for its lovely bright yellow flowers and followed in autumn by attractive berries. It is evergreen or semi ever green depending on where it is grown, and will shed its leaves when grown in colder areas. Hypericum will tolerate most conditions and it tends to be vigorous. Hypericum will put up with drought and shade, (although flowers best in sun) but dislikes waterlogged, damp soils. Hypericum has a long flowering season and carries a profusion of blooms as the image top right illustrates. There is no need to prune other than to remove any dead wood in the spring. There are several varieties with different growing habits : Hypericum Calycinum is a low growing spreading type, only 60cms high and is good for grown cover. It will spread quickly, quite vigorously, and is bordering invasive and each plant will spread up to 1.5. Hypericum Inodorum Elstead is quite different, upright and bushy up to 1m with 1m spread.
Hypericum Hidcote image left is a very popular variety which has RHS garden merit award and grows up to around 1.2m so suitable for the back of the border and even for hedging.
There are also dwarf varieties suitable for front of the border or rock gardens such as Pallens
A light prune in early spring if you want to restrict size or tidy up. However, H. calycinum which is vigorous and can be prone to rust benefits from being cut back annually to the ground in around february /March time. Generally Hypericum flowers from July to October.
Hypericum self seed and can be prone to rust. To reduce the problems with rust the shrub can be cut down at the end of summer and all the rusty leaves removed for a fresh start in the spring. It will still flower and produce berries as Hypericum flower on the current years wood.
Another plus point of Hypericum is that it is ideal for cut flowers both the blooms and later the berries.
For explanation about frost hardy