The term “butterfly tree” suggests a plant that serves as a powerful magnet for these winged insects. The plant most commonly associated with this name is the genus Buddleja, specifically Buddleja davidii, often called the butterfly bush. This popular ornamental shrub is celebrated for its prolific, showy flowers and its ability to draw numerous butterflies, leading many gardeners to seek it out for creating pollinator habitats.
Defining the Butterfly Tree
The plant known as the butterfly tree is scientifically classified as Buddleja davidii, a species native to China and Japan. Although frequently called a “tree,” it is technically a deciduous, multi-stemmed shrub. It typically reaches heights of 6 to 12 feet and is characterized by arching stems and a vigorous, bushy growth habit.
The leaves are lance-shaped, growing up to 10 inches long, and are sage-green on top with a distinctive white, woolly underside. The shrub’s most recognizable feature is its flowers, which are densely clustered in long, spike-like terminal panicles measuring 6 to 18 inches in length. These clusters of tiny, tubular flowers originally appeared in shades of lilac or purple with an orange throat.
Extensive cultivation has led to numerous named varieties, expanding the flower color palette to include pinks, whites, deep purples, and yellows. The size and density of the inflorescence, combined with its long bloom time from summer into fall, make it a visually striking addition. While it does not achieve the trunk size of a true tree, its impressive stature contributes to the common, though botanically inaccurate, name.
The Attractant: Why Butterflies Love It
The primary reason Buddleja davidii is effective at attracting butterflies lies in the quality and quantity of the nectar it produces. The flowers offer a copious supply of nectar with a notably high sucrose content, providing a rich, easily accessible energy source for adult butterflies.
The structure of the individual flowers is also suited to long-tongued insects like butterflies. Each small, tubular flower possesses a corolla tube, perfectly shaped for a butterfly’s proboscis to reach the nectar deep inside. The flowers also emit a mild, musky fragrance that, along with their bright colors, acts as a beacon for pollinators.
Studies suggest that the scent, which contains chemical compounds like oxoisophorones, may be more attractive to some butterflies than the visual cues of the blooms. It is important to note a distinction: Buddleja davidii serves only as a nectar source for adult butterflies, not as a host plant. The leaves do not support the development of butterfly or moth larvae (caterpillars), which require specific native plants to complete their life cycle.
Cultivation and Control
The butterfly bush is easily grown in average, well-drained soil and requires full sun to thrive and produce blooms. It is known for its tolerance of poor soils and drought once established, making it a low-maintenance choice. However, it will become sparse and flower poorly in shaded or wet conditions.
Effective maintenance involves hard pruning, performed in late winter or early spring before new growth begins. Cutting the stems back close to the ground encourages vigorous new growth, which produces the best flowers. This annual pruning helps maintain a desirable shape and promotes flowering throughout the summer.
A concern with Buddleja davidii is its invasive status in many regions, including the United States and the United Kingdom. The plant produces abundant, tiny seeds housed in capsules that are easily dispersed by the wind. This allows it to rapidly colonize disturbed areas like roadsides and riverbanks. This aggressive naturalization displaces native vegetation, reducing the availability of host plants for native insects.
Responsible gardening practices are necessary to mitigate this environmental risk. Promptly removing spent flower spikes, a process called deadheading, before they can set seed is the most effective way to prevent its spread. Alternatively, gardeners should consider planting newer, sterile cultivars, such as those with “Chip” or “Miss” in their names. These varieties are specifically bred to produce little to no viable seed, allowing for butterfly attraction without the invasive potential.