Dahlias are a popular sight in late-summer gardens, offering a stunning array of colors and forms that can extend blooms well into the cooler months. For gardeners seeking to provide sustenance for local pollinators, the question of whether bees like dahlias is complex. The answer depends entirely on the specific variety chosen. Many modern cultivars offer little benefit, while others are a powerful source of late-season food for bees, butterflies, and hoverflies.
The Physical Barrier: Why Dahlia Structure Matters
The variability in a dahlia’s value to pollinators stems from centuries of cultivation and hybridization. Wild dahlias possess a simple, open structure, but breeders have selected for complex, multi-layered flowers. This process often converts the dahlia’s reproductive parts, which hold the food resources, into extra petals.
A dahlia flower is a composite, made up of ray florets (the showy petals) and disk florets (the tiny structures in the center). Bees seek the pollen and nectar found within these central disk florets. In highly bred varieties, the stamens and pistils are replaced by petaloid formations, creating the dense, fluffy appearance of a double flower.
This modification physically obscures or completely eliminates the food source. When the central disk is buried under layers of petals, the flower provides no accessible benefit to foraging insects. The physical structure of the bloom acts as a barrier, dictating whether the flower is a source of nutrition or merely a decoration.
Varieties Bees Prefer (Accessible Pollen and Nectar)
For gardeners seeking to support local ecosystems, choosing dahlias with open centers is the most effective strategy. These varieties closely resemble the original wild species, making their pollen and nectar readily available and visible to foraging insects. By focusing on these accessible forms, you ensure that bees, including bumblebees and honey bees, can easily land and gather necessary late-season forage.
Several types are excellent choices for pollinators:
- Single-flowered dahlias are the most reliable choice, featuring a single ring of ray petals surrounding a wide, exposed central disk.
- Mignon dahlias are naturally shorter and share the same simple, open structure.
- Collarette dahlias have a distinctive, accessible center surrounded by a ring of short, often twisted petals, backed by a ring of larger outer petals. Examples like the ‘Bishop of Llandaff’ are excellent bee magnets.
- Anemone-flowering dahlias also perform well, as their centers are composed of a raised, cushion-like cluster of tube-shaped florets packed with pollen. Specific groups like the ‘Happy Single’ series are bred for their open centers and strong performance.
Highly Decorative Varieties Bees Avoid
In contrast to the open-centered varieties, many highly decorative dahlias offer little to no nutritional value to bees. These cultivars have had almost all their reproductive parts converted into layers of petals. The resulting dense structure makes it impossible for a bee to reach any resources that might remain.
Common types to avoid if supporting pollinators is the goal include Pom-Pom, Ball, Cactus, and Dinner Plate dahlias. The massive, tightly packed blooms of a Dinner Plate dahlia, for instance, result from the total conversion of stamens into petaloid formations, leaving the flower functionally sterile.
The physical density of these flowers means a bee cannot navigate the tightly packed petals to find nectar or pollen. These stylized dahlias prioritize petal count over biological function. When selecting tubers, check the classification; if the description includes terms like “double,” “fully double,” or “decorative,” it is likely an unproductive choice for pollinators.