Hypericum is commonly known as St John's wort. Most varieties are deciduous or semi evergreen and summer flowering with lovely bright yellow flowers and followed in autumn by attractive berries. There are many varieties but those commonly sold and grown in gardens are H.x hidcoteense 'Hidcote' and H. calycinum 'Brigadoon'.
Hypericum is easy to grow being tolerant of most growing conditions and it is vigorous with a tendency to self seed. It is very tolerant, 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 also dwarf varieties suitable for front of the border or rock gardens such as Pallens.
Another plus point of Hypericum is that it is ideal to have as a cut flower both the blooms and later the berries are attractive and frequently used in flower arrangements.
Between 2015-2018 the RHS undertook a trial of Hypericum assessing varieties for shrub shape, flower quality and length of flowering, autumn fruits and disease resistance. If you are looking for a variety to grow these are a good starting point,
New AGMs were awarded to H. beanii 'Precious Sun' which grows up to 1.5m; H.x dummereri 'Peter Drummer' a ground cover variety growing to 45cms, H. Henryi subsp hancockii ' September Sun' a taller variety growing to 2m; H. lancasteri growing up to 1.2m; H. oxyphyllum 'Golden -Ness' which is compact with coppery new growth up to 1.2m and H.pseudohenryi up to 1.8m. Flowering times vary a little starting the earliest in June to late flowering on October all with yellow flowers.
Those which retained their AGM are H.forrestii, H.x hidcoteense 'Hidcote' and H. Kouytchense.
Hypericum Hidcote image top left is a popular variety readily available which grows up to around 1.2m so suitable for the back of the border and even for hedging.
Also H. x moserianum is a dwarf variety growing up to .5m with reddish stems and very hardy H5.
Hypericum kouytchense is another short variety up to .5m with large flowers and good autumn berries. Most of these varieties are readily available.
For an explanation about frost hardy