Dense St Johnswort, Hypericum densiflorum is another native St Johnswort with many small yellow flowers. This 4′ to 6′ shrub has thousands of 1/2″ bright yellow flowers from July through September. It has an upright oval form and is hardy in zones 5 to 8. This is a stunning shrub in the late summer. The yellow flowers are a great pollen source for bees and other pollinators.