Physostegia is a genus of herbs belonging to the Lamiaceae family, or mint family, and it consists of 12 species. The genus name is from the Greek words physa, which means “bladder,” and and stege, which means “covering,” referring to the appearance of the calyx of the flower. Physostegia are flowering perennials native to eastern North America. The most common species is the Physostegia virginiana, commonly known as the obedient plant or false dragonhead.
The flowers bloom in upright spires in shades of pink, purple or white, and they resemble snapdragons in appearance. Physostegia flowers are referred to as obedient because they are easy to arrange in new positions on the stem. Depending on the species, physostegia will bloom from late summer through the fall and into early winter. The blooms make for long-lasting cut flowers.
Fully grown plants typically stand 1-4 feet (30.5-122 cm) in height but can be as tall as 6 feet (183 cm). The stems are non-woody and square-shaped, which are characteristics of plants in the mint family. The leaves are dark green on top and a lighter shade of green on the reverse side, and they are narrow with serrated edges. The plant overwinters as a rosette of leaves without stems or flowers.
Physostegia are a popular choice as garden perennials. They are easy to propagate by seed or division, and the blooms are an attractant for hummingbirds and butterflies. They also are a popular choice as a deer-resistant planting.
The native range of Physostegia is eastern North America, from Quebec to Manitoba in the north and south to Texas, Louisiana, Alabama and Georgia. They tend to be found growing wild in swampy areas and on other soils that are not well drained. Ideal conditions for cultivation of physostegia include moist soils in the pH range of 5-7, with sun to light shade exposure.
These plants should be fertilized frequently, covered with mulch in the fall, and divided every two to three years. One disadvantage of physostegia is that they tend to be invasive and can spread aggressively if left untended. Spreading occurs through rhizomes, which are creeping rootstalks, although roots of the plants are shallow and can be easily dug up. Spreading can either be discouraged with barriers or kept in check by division and replanting. Physostegia can also be grown as potted plants.