The dahlia, a tuberous perennial native to Mexico and Central America, is a popular garden flower known for its incredible diversity in size, shape, and color. These plants are members of the Asteraceae family, and their blooms are technically composite flower heads. The question of whether these vibrant flowers attract pollinators has a nuanced answer that depends almost entirely on the specific variety grown. While some modern, heavily cultivated dahlias offer little reward, others provide an accessible and abundant source of sustenance for garden insects.
Why Dahlia Structure Determines Attraction
The ability of a dahlia to attract and feed pollinators is governed by its flower structure, which is a result of horticultural breeding. A dahlia flower head is composed of two main parts: the outer, showy petals known as ray florets, and the central, reproductive structures called disk florets. Only the small, tubular disk florets produce the pollen and nectar that pollinators seek.
The original, wild dahlia species had open centers, exposing the disk florets to visiting insects. However, breeders have selected for “double” blooms, where the disk florets have genetically transformed into extra petal-like ray florets. This structural change results in the large, dense, “fluffy” flowers often seen in gardens, but it effectively seals off the pollen and nectar sources, making them inaccessible to most bees and butterflies. For a pollinator to benefit, the dahlia must have an open center where the disk florets are clearly visible and reachable.
Identifying Pollinator-Friendly Varieties
Gardeners looking to support pollinators should focus on dahlia varieties that retain the open-centered structure of the wild species. These types are easily identifiable because their reproductive parts are plainly visible in the center of the bloom. Single-flowered dahlias are excellent choices, featuring a single, uniform row of ray florets surrounding a large, exposed disk of pollen-rich tubular flowers. Their open nature makes the pollen and nectar readily available, especially to bees and hoverflies.
Mignon dahlias are a smaller, compact subgroup of the single-flowered type, typically featuring blooms under two inches in diameter on shorter plants. They share the same beneficial open center structure and are ideal for containers or the front of a border. Collarette dahlias also provide easy access, distinguished by a ring of small, petal-like structures (petaloids) that sit between the outer ray florets and the central disk, creating a distinct two-layered look. These open-faced forms, such as the Anemone-flowered types, are favored by a variety of pollinators because they offer a clear landing pad and a visible, abundant food source.
Gardening Practices to Increase Pollinator Activity
Planting the correct dahlia varieties is the first step, but specific gardening practices can further enhance their attractiveness to local insect populations. To create a highly visible target, dahlias should be planted in large groups or drifts of the same type and color. Grouping plants makes the floral display more visually dense, helping foraging insects locate the food source more efficiently. Avoiding the use of systemic pesticides is necessary, as these chemicals can harm the beneficial insects that visit the flowers.
Gardeners should also ensure a continuous food supply by companion planting their open-centered dahlias with other high-nectar sources that bloom at different times. Maintaining a continuous cycle of blooms, from mid-summer until the first frost, allows dahlias to function as an important late-season food source for bees and butterflies preparing for winter. Regular deadheading of spent blooms encourages the plant to produce more flowers, extending the availability of pollen and nectar.