Verbena is a widely cultivated flowering plant, cherished by gardeners for its long blooming season and vibrant clusters of flowers that attract pollinators. The genus Verbena and the closely related Glandularia contain a variety of species, making the question of whether they are perennials surprisingly complex. The answer depends entirely on the specific plant’s genetics and the climate where it is grown, as the distinction between an annual and a perennial is often blurred by a plant’s ability to survive winter temperatures.
Classification by Lifecycle
Understanding plant lifecycles provides the foundation for determining if a Verbena will return year after year. An annual plant completes its entire life cycle—germinating, flowering, setting seed, and dying—within a single growing season. In contrast, a true perennial lives for multiple years, with its root structure surviving the winter to produce new growth in the spring.
The complexity arises with the term “tender perennial,” which describes a plant that is genetically perennial but cannot tolerate frost or freezing temperatures. These plants grow continuously in warm climates but are killed by winter in colder regions. Gardeners often treat a tender perennial as an annual, replanting it each spring. Many Verbena species fall into this category, behaving as either an annual or a perennial depending on the local environment.
Key Garden Varieties and Their Classification
Verbena species commonly found in gardens can be separated into groups based on their inherent hardiness. The popular trailing or mounding varieties sold for hanging baskets and containers are often hybrid garden verbenas (V. x hybrida or Glandularia x hybrida). These are short-lived perennials hardy only to USDA Zones 9 or 10, meaning they are grown as annuals in most of North America.
A distinct variety is the tall, airy Brazilian Verbena (V. bonariensis), which is a true herbaceous perennial in milder climates. This species is hardy in Zones 7 through 11, returning from the crown each spring. Even in cooler areas, V. bonariensis often appears perennial because it readily self-seeds, dropping seeds that sprout new plants the following season.
How Climate Dictates Hardiness
The primary factor determining a Verbena’s perennial status is the minimum temperature it can withstand. The USDA Hardiness Zone system maps geographic regions based on their average annual minimum winter temperature. A Verbena labeled a perennial is only a perennial within its specified hardiness range.
For example, a species designated as hardy to Zone 7 will reliably return in Zone 7 and all warmer zones. If that same plant is grown in a colder area, like Zone 6 or below, freezing temperatures will penetrate the soil deeply enough to kill the plant’s roots, forcing the gardener to treat it as an annual. The plant’s survival depends on the root ball staying insulated from prolonged, deep freezes. In borderline zones, a mild winter may allow survival, but a severe one will cause the plant to die back completely.
Overwintering and Care for Tender Varieties
Gardeners in colder climates can successfully keep tender Verbena varieties alive through winter with specific care practices. For those in zones slightly colder than the plant’s listed hardiness, heavy mulching can provide enough insulation. Applying a thick layer of straw or wood chips over the root zone in late autumn helps stabilize the soil temperature and prevent lethal freezing.
In much colder zones, the best method for preserving a tender Verbena is to bring it indoors. Before the first hard frost, the plant should be cut back by about one-third and either dug up or moved if already in a pot. The plant can then be kept in a cool, bright location, such as a garage or unheated sunroom, to induce semi-dormancy. Another reliable technique is taking semi-ripe cuttings in late summer, rooting them in a sterile medium, and overwintering the small new plants in a frost-free environment until spring.