Cymes of the purpletop verbena are balanced upon long slender stems putting them within convenient reach of passing butterflies.
Purpletop verbena is an erect, clump-forming perennial with stiff, widely branched stems. It can reach 3-6 ft (0.9-1.8 m) in height with an open, airy spread of 1-3 ft (0.3-0.9 m). The scabrous (sandpapery) stems and branches grow in an upright pattern and are square in cross section. Most of the leaves are clustered in a mounded rosette at the base of the plant. The relatively scarce stem leaves are opposite, 3-5 in (7-13 cm) long and clasping (i.e. the leaves have no petioles and their bases wrap around the stem). The flowers are purple, a quarter-inch across, and borne in rounded clusters about 2-3 in (5-7.6 cm) across. Botanists call this type of inflorescence a cyme: a flower cluster in which the center flower opens first, and later-opening flowers are on the ends of lateral branches that arise from below the first flower. Purpletop verbena displays its showy flowers all summer long, until the first frost of autumn.
Purpletop verbena is native to Brazil and Argentina. It has escaped cultivation and become naturalized in disturbed areas in California and the southeastern US, from South Carolina to Texas, including all of Florida.
Pinch the first few shoots in spring to encourage branching. The more you cut it back, the more shrub like purpletop verbena will become. This plant often contracts powdery mildew, especially in humid summers. This causes unsightly white spots on the leaves but does not seem to have any effect on the health of the plant or on its blooming. Light: Does best in full sun but can tolerate a little bit of shade. Moisture: Purpletop verbena is fairly drought tolerant. Hardiness: This verbena is a perennial in USDA zones 7-11 and grown as an annual in cooler climates. Propagation: Purpletop verbena is easily propagated from seed and it usually volunteers to do just that, whether it's in the gardener's design plan or not! It also can be started from cuttings of young branch tips in spring or summer, or by dividing the rooted clumps of young shoots in spring.
Purpletop verbana can grow to airy heights of about 3 to 6 ft (0.9-1.8 m) although it often flops over if not supported as seen here.
The airy, see-through habit of purpletop verbena makes it a good choice for the front or middle of a mixed border. It doesn't cast much of a shadow and you can see other plants behind and under it. Weave a line of purpletop verbena through a bed or border of other butterfly flowers. It's best planted in columns or masses because it is so thin it will be overlooked all by itself.
In mild climates, purpletop verbena will self sow rather freely. However, it is easily kept under control. Although it has become established in many areas outside its native range, it is not considered a pest.
There are some 250 species of Verbena and about a half dozen are in cultivation. The most popular is the annual bedding plant, hybrid verbena (V. X hybrida), the product of artificial crossing among several wild species. Various cultivars of this annual are available at most garden centers. Moss verbena (Glandularia puchella, formerly known as Verbena tenuisecta), is a closely related vervain originally from South America that now grows prolifically in fields and along southern US road shoulders. Moss verbena often produces huge expanses of brilliant red or purple by staying close to the ground below the mowers' blades.