Verbena officinalis, the common vervain or common verbena, is a perennial herb native to Europe. It grows up to 70 cm high, with an upright habitus. The lobed leaves are toothed, and the delicate spikes hold clusters of two-lipped mauve flowers.
During their blooming period, give them a thorough watering once a week if they do not receive an inch of rain that week. Avoid overhead watering. If bloom slows during the summer, trim the whole plant back by about one fourth of its height and spread, water thoroughly and fertilize lightly
Verbenas are not heavy feeders, but they do appreciate a monthly application of balanced, slow-release flower fertilizer to help them keep up the flower show, which can last from spring until frost
In cold conditions Verbena bonariensis can suffer dieback if cut back in autumn, so it's best to leave the plant until spring and cut back the old growth when you see the new shoots emerging at the base.
Lower temperatures can be used as a way to tone and slow growth; however, low temperatures also delay flowering, especially if under low light conditions.
