The presence of ants on a hydrangea signals a secondary issue rather than an attraction to the plant itself. Ants do not feed on hydrangea foliage, roots, or flowers, so the shrub is not their direct target. Their appearance is a reliable indicator that a different type of insect is actively feeding on the plant. Seeing a line of ants traveling up and down the stems of a hydrangea should prompt the immediate inspection of the leaves and buds for other pests.
The Indirect Attraction
Ants are drawn to the hydrangea by honeydew, a sweet, sticky waste product. Honeydew is excreted by sap-sucking insects that feed on the plant’s vascular tissue. These pests consume large volumes of sugary sap, expelling the excess as a carbohydrate-rich liquid that coats the leaves and branches.
This honeydew is a high-energy reward for ants. Certain ant species have developed a symbiotic relationship with the honeydew producers. Ants actively “farm” these insects, protecting them from natural predators like ladybugs and parasitic wasps to ensure a continuous supply. They even use their antennae to stimulate the honeydew producers, encouraging them to release the sugary droplets.
Identifying the Real Culprits
The sap-sucking pests responsible for honeydew are typically aphids, scale insects, or mealybugs. Accurate identification is the first step, as their removal is the only effective way to deter the ants permanently. Ants will only leave the plant once their food supply is eliminated.
Aphids
Aphids are the most common culprits, appearing as small, soft-bodied, pear-shaped insects. They are often found in clusters on new growth, leaf undersides, and flower buds, ranging in color from pale green to black. Their feeding causes leaves to become distorted or yellowed.
Scale Insects
Scale insects are harder to identify because they are stationary and often look like small, oval bumps or waxy growths on the stems or leaf veins. These insects cover themselves with a protective shell that makes them difficult to treat.
Mealybugs and Damage
Mealybugs are recognized by their white, cottony or woolly appearance, often hiding in leaf axils or along the veins. All three pests pierce the plant tissue to suck out the sap, weakening the hydrangea over time. The resulting honeydew can also promote the growth of sooty mold, a black fungus that reduces the plant’s ability to photosynthesize.
Managing Pests and Ants
Eliminating the primary pests must be the focus of any management strategy, as simply killing the ants will only result in new ants arriving to claim the honeydew. A strong, targeted jet of water from a garden hose is a simple, effective method for dislodging aphids and mealybugs. This physical removal should be repeated every few days, targeting the undersides of leaves where pests often hide.
For heavier infestations, low-impact horticultural treatments are recommended. An application of insecticidal soap or neem oil is effective against soft-bodied insects like aphids and mealybugs. These products work by smothering the pests and should be applied thoroughly, covering all plant surfaces, including the stems. Horticultural oil is useful against the protective shells of scale insects, but apply it during the plant’s dormant season or on overcast days to prevent leaf burn.
Cultural controls also support the hydrangea’s natural defenses and reduce pest susceptibility. Ensuring good air circulation through proper spacing and pruning helps manage humidity, making the environment less hospitable to pests and sooty mold. Maintaining the overall health of the hydrangea through appropriate watering and soil conditions limits the stress that attracts sap-sucking insects.