Marigolds are often planted near vegetables hoping their pungent aroma will deter unwanted visitors. This popular gardening lore leads many to wonder if marigolds also repel beneficial insects, especially bees, which are necessary for garden success. Unraveling this common myth requires examining the plant’s chemical composition and how different insects perceive its presence. This clarifies the specific pests marigolds manage and explains the true relationship between these flowers and pollinators.
The Truth About Marigolds and Bees
The idea that marigolds drive away pollinators like honeybees and bumblebees is not supported by scientific observation. While the strong scent of the foliage may be off-putting to some humans and certain insects, it does not deter bee species from visiting the flowers. Bees possess a different sensory apparatus than many garden pests, relying on visual cues and specific chemical signals that override any general repellent effect.
Marigolds, particularly French and African varieties, are readily visited by many types of bees seeking resources. The flowers offer both nectar, a sugar-rich energy source, and pollen, which provides protein and fats essential for rearing their young. For a bee focused on foraging, these rewards are far more compelling than the volatile organic compounds given off by the plant tissue. Observations frequently show bees actively foraging on marigold blooms, confirming they are not repelled.
What Marigolds Actually Repel
The marigold’s reputation as a pest deterrent is not entirely unfounded, but its effectiveness is highly specific. The primary scientific basis for its use in companion planting concerns the control of microscopic soil pests. Marigold roots release compounds specifically toxic to plant-parasitic nematodes, which are tiny roundworms that attack the roots of many garden vegetables.
The most potent chemical responsible is alpha-terthienyl, a sulfur-containing thiophene derivative exuded by the roots. This compound is nematicidal, meaning it kills or inhibits the development of nematodes, such as the destructive root-knot species (Meloidogyne incognita). The marigold’s protective function is largely subterranean, protecting nearby plants from unseen soil damage. While the foliage contains volatile oils like linalool, which may deter certain flying pests, this effect is often minor and dependent on the specific marigold cultivar and pest species.
Why Bees Visit Marigolds
Bees are attracted to marigolds by visual and resource-based factors that counteract any mild repellent properties. The bright yellow and orange colors are highly visible to bees, which see light in the ultraviolet spectrum. These vibrant hues serve as clear signals guiding pollinators to a potential food source.
Once a bee approaches, the flower’s structure determines the accessibility of its rewards. Single-petal varieties, sometimes called open-faced marigolds, are significantly more attractive and beneficial to pollinators than highly hybridized types. These open blooms allow easy access to the central disk flowers, which are rich in pollen and nectar. In contrast, “double bloom” or “pompom” cultivars often have their reproductive parts modified into extra petals, making the nectar and pollen difficult or impossible for bees to reach.
Plants That Deter Flying Insects
Gardeners seeking plants that actively repel flying nuisance insects, such as mosquitoes and houseflies, should turn to herbs rich in strong essential oils. These plants release volatile organic compounds that disrupt the sensory organs of many pests. Rosemary, for instance, contains a distinctive oil unpleasant to many insects, making it an excellent choice near outdoor seating areas.
The familiar scent of citronella grass (Cymbopogon nardus) or lemongrass (Cymbopogon citratus) is derived from citronellal, a compound effective against mosquitoes. Similarly, basil, lavender, and mint all produce strong-smelling oils that help keep pests away. The compounds in these herbs, like menthol in mint or linalool in lavender, act as natural deterrents that confuse or repel flying insects without harming the beneficial bee population.