Hydrangeas are one of the most popular shrubs in home gardens, but the presence of flies gathering around the large, colorful blooms often leads gardeners to wonder if the plant is a direct attractant. While some flowers are specifically designed to lure flies for pollination, the presence of these insects on a hydrangea is usually an indirect result of other conditions within the garden ecosystem. Understanding the true cause allows for targeted and effective management, ensuring the plant remains healthy and the area stays comfortable.
The Relationship Between Hydrangeas and Common Flies
Hydrangeas are not generally considered “fly-attracting” plants in the same way that plants relying on strong, decaying scents are. The flowers of many common hydrangea varieties, particularly the large, sterile florets found in mophead types, offer little accessible nectar or pollen for insects like house flies. Their primary function is visual appeal, and they often lack the powerful, sweet fragrance that draws many other pollinators.
However, some types of hydrangeas, especially the lacecap varieties and certain panicle hydrangeas, do contain small, fertile florets that produce nectar and pollen. These can attract various insects, including flies, bees, and butterflies. Flies belong to the order Diptera, and those that visit the fertile flowers are generally seeking a minor food source, not a dedicated breeding site. If a large swarm of common house flies or other nuisance flies is present, the plant’s inherent floral biology is likely not the main issue.
Identifying Secondary Attractants
The primary reasons flies gather around hydrangeas stem from environmental factors or the presence of other pests, often referred to as secondary attractants.
Honeydew
One of the most significant factors is the presence of honeydew, a sticky, sugary residue excreted by sap-sucking insects like aphids, scale, or whiteflies. These pests feed on the plant’s phloem, which is rich in sugar, and then expel the excess as a clear liquid that coats the leaves and stems beneath them. Honeydew is a highly concentrated food source that is extremely appealing to common house flies and yellow jackets. The flies are drawn to this sweet substance, treating the hydrangea as a feeding station rather than a host plant. The presence of these small, sugar-feeding insects should be investigated if a persistent fly problem exists, especially if the leaves feel sticky or appear shiny.
Decaying Material and Moisture
Another common cause involves decaying organic material, which attracts flies looking for moisture and breeding grounds. Hydrangeas are often grown in mulched beds, and if spent blooms, fallen leaves, or old mulch are allowed to accumulate at the base of the shrub, they create an ideal environment for nuisance flies. Furthermore, hydrangeas prefer consistent moisture, and overly wet or poorly draining soil can contribute to the proliferation of fungus gnats. This small fly species thrives in damp, fungal-rich conditions and is a sign of excess soil moisture.
Practical Strategies for Fly Management
Management of flies around hydrangeas should focus on eliminating the secondary attractants, which are the root causes of the problem.
Sanitation is a straightforward and effective first step, involving the removal of any decaying organic matter from the plant’s base. Prune off spent or dead blooms promptly, and clear away leaf litter and old mulch to deny flies potential breeding and feeding sites.
If honeydew is the identified attractant, the focus must shift to controlling the sap-sucking pests producing it. These insects can often be managed with targeted, low-impact treatments such as insecticidal soap or horticultural oil, which work by suffocating the pests upon contact. It is important to apply these products thoroughly, ensuring coverage of the undersides of the leaves where aphids and whiteflies often hide.
Adjusting watering practices can also help mitigate issues with fungus gnats and decay-attracted flies. Ensure the hydrangea has proper soil drainage, as consistently soggy soil is an invitation for fungus and moisture-loving pests. Allowing the top inch or two of soil to dry slightly between waterings discourages the environment preferred by fungus gnat larvae. For a non-chemical method against honeydew, a strong jet of water can be used to periodically wash the leaves, physically dislodging pests and rinsing away the sticky sugar residue before it attracts flies.