The dahlia flower, native to the high elevations of Mexico and Central America, is a globally popular garden and cut flower celebrated for its spectacular, vibrant blooms and diverse forms. These tuberous perennials offer an extended display from midsummer until the first frost. Whether dahlias benefit garden biodiversity, particularly pollinators, depends almost entirely on the specific flower structure. This nuance stems from the complex history of hybridization, where human preference for visual drama often created a structural barrier for foraging insects.
The Structural Barrier: Why Some Dahlias Fall Short
The original wild dahlia species possessed a simple, single-petal structure that openly displayed its reproductive center. Modern hybridization efforts, however, have focused on increasing the petal count to create the dense, show-quality blooms often seen at flower shows. This process, known as “doubling,” causes ray florets—the showy, outer “petals”—to proliferate, often at the expense of the disc florets, which are the tiny, tubular flowers in the center that contain pollen and nectar.
In varieties like the giant Dinnerplate, Pom-pom, or Cactus dahlias, the sheer volume of petals completely conceals or physically blocks the central disk. The tightly packed layers of florets make it impossible for most insects to access the pollen and nectar beneath. These highly bred cultivars are essentially sterile from an ecological standpoint, providing little to no nutritional reward for foraging bees or butterflies.
This structural modification is the primary reason for conflicting information about the dahlia’s value to pollinators. The plant itself is capable of producing the necessary resources, but the physical architecture of many popular cultivars prevents access. Therefore, a gardener must look for varieties that retain the structure of the wild ancestors to ensure an accessible food source.
Identifying the Best Varieties for Pollinators
Gardeners looking to support local biodiversity must select dahlia types that have an easily visible and open center, known as the central disc. This disc is where the pollen and nectar are produced, making it the target for foraging insects. The most reliable options closely resemble the original single-flowered form, featuring only one or two rows of ray florets.
The most pollinator-friendly groups include Single Dahlias, which have a single ring of flat petals surrounding a prominent yellow or orange center. Mignon Dahlias are a smaller, compact version of the Single type, perfect for containers, with their petite open centers readily available. These simple forms provide a large, exposed landing pad and an obvious food source.
Other excellent choices are Collarette and Anemone-flowered dahlias, which also feature open access to the central disc. Collarette varieties have a distinct ring of smaller, often contrasting, inner petals that form a “collar” around the central disc. Anemone types have a cushion of tubular florets in the center, resembling a pincushion, which is still fully accessible to insects. These varieties provide a continuous source of food from midsummer until the first frost.
The Specific Pollinators Attracted
Open-centered dahlias attract a range of generalist pollinators, providing them with both pollen and nectar resources late in the season. Honeybees and various species of bumblebees are frequent visitors to these single and semi-double blooms. Bees are particularly drawn to the exposed central disc, where they can easily collect the protein-rich pollen.
Butterflies, including Monarchs, are also highly attracted to the large, brightly colored, open blooms, which offer a perfect landing platform. Their long proboscises allow them to reach the nectar in the central disc florets. Additionally, other beneficial insects, such as hoverflies and skippers, are commonly observed foraging on these accessible dahlia types.
While dahlias are not traditionally considered a primary food source for hummingbirds, the bright colors of single varieties can occasionally draw them in. However, the flower structure is more optimally suited for insects than for the long beaks of hummingbirds. The consistent availability of pollen and nectar in open varieties makes them a valuable addition to the garden.