Hypericum prolificum, also known botanically as St. John's Wort, is a larger herbaceous and woody shrub form of the typically low-growing St. John's Wort ground cover. The shrub version produces large numbers of yellow flowers in the late summer and fall. It can become leggy and produce fewer blooms over time, without rejuvenation pruning to urge new shoots and more flowers. This plant is such a vigorous grower that drastic rejuvenation pruning can be done every spring and the plant will still be able to restore its leafy and flower-filled form by the summer bloom time.
Prune your Hypericum prolificum in the spring, ideally in March or April, but certainly no later than May or the late-summer bloom may be disrupted or diminished.
Shear the entire shrub down to just 2 to 4 inches above the soil surface with long-blade pruning shears. This hard pruning will spur rapid development of new shoots, and the entire shrub will leaf out and flower within the same season when provided ample water and sun.
Collect all of the clippings that fall into the shrub interior and to the soil below, as these can breed disease and pests as they decay. They can also lay across new growth making the shrub look untidy.