The genus Buddleia, commonly known as the butterfly bush, is a fast-growing, deciduous, or semi-evergreen flowering shrub popular in gardens worldwide. It is cultivated for its long, showy bloom period and its powerful ability to attract winged insects, particularly adult butterflies. This article explores the physical structure of Buddleia, its role in the garden ecosystem, and the management required for its vigorous growth.
Defining Characteristics and Appearance
The physical structure of Buddleia is characterized by rapid growth and distinct foliage. Most species, particularly Buddleia davidii, grow as large, arching shrubs that can reach heights of 5 to 10 feet in a single season if left unpruned. The leaves are typically lance-shaped and arranged in opposite pairs along the stems, often displaying a grayish-green hue on the upper surface. The undersides are frequently covered in fine, whitish hairs, giving them a slightly silvery appearance.
The flowers are the plant’s most recognizable feature, emerging in dense, elongated clusters called panicles. These conical or pyramidal spikes measure between 4 and 12 inches long and bloom continuously from mid-summer until the first frost. Each panicle is composed of numerous small, tubular florets that are deeply fragrant, emitting a sweet, honey-like scent. Flower colors span a broad spectrum, including shades of purple, pink, lilac, white, and even yellow or orange in certain cultivars.
Attraction to Butterflies and Other Pollinators
The moniker “Butterfly Bush” relates directly to the plant’s high output of nectar, a potent energy source for adult pollinators. The tubular shape of the individual flowers allows butterflies, bees, and moths easy access to the copious nectar produced inside. This nectar is rich in sucrose, a sugar that provides quick fuel for the active metabolism of adult insects.
The flowers act as a powerful attractant, drawing in numerous species of adult butterflies, such as the Red Admiral, Peacock, and Small Tortoiseshell, along with bees and hummingbirds. While the plant provides energy for adult stages, it offers no nutritional value for the larval stages of native butterflies. No North American butterfly or moth species can complete its life cycle by feeding on Buddleia leaves, meaning the plant does not serve as a host for caterpillars.
Managing Vigorous Growth and Spread
The vigorous nature of Buddleia means annual maintenance is necessary to keep the plant within bounds. In many temperate regions, the common species B. davidii is considered invasive because of its prolific self-seeding. The small seeds are easily dispersed by the wind, allowing the shrub to rapidly colonize disturbed sites, such as railway embankments and waste grounds, where it can outcompete native flora.
To manage its size and encourage robust flowering, the shrub should be hard pruned, often called the “Buddleia Hack,” in late winter or early spring. This involves cutting the previous year’s growth back significantly, typically down to a low framework of stems about one to three feet tall. Removing spent flower heads, a process called deadheading, is also necessary to prevent the formation and spread of seeds. Recognizing the invasive potential, plant breeders have developed sterile or low-fertility cultivars, such as the ‘Buzz’ or ‘Lo & Behold’ series. These hybrids offer the same visual and pollinator appeal without the risk of uncontrolled spread, providing a responsible choice for gardeners.