When you discover your beautiful hydrangea stems have been clipped, stripped, or bored into, the frustration is understandable. This damage is a common issue for gardeners, and pinpointing the culprit is the first step toward effective treatment. Stem damage on hydrangeas is generally caused by one of two categories of pests: larger mammals that leave obvious physical wounds, or smaller insects that cause localized, internal destruction. By carefully examining the type and location of the damage, you can accurately diagnose the problem and take specific action to protect your shrubs.
Large Pests That Clip and Strip Stems
Mammalian pests often leave obvious damage to woody stems. The most common culprits are deer and rabbits, whose feeding habits are distinct due to their anatomy. Deer lack upper incisor teeth, forcing them to press their lower teeth against a hard palate and tear the vegetation. This tearing action leaves a ragged, shredded edge on the remaining stem or branch, typically found above three feet.
Rabbits, conversely, have sharp incisors that allow them to make a very clean, slanted cut through the stem. This damage is usually found much closer to the ground, often only a few inches high. Rabbits also tend to gnaw the bark off the base of the stem, especially when other food sources are limited. Voles cause a different kind of damage by gnawing on the bark and roots at or just below the soil line. Their feeding leaves irregular, patchy gnaw marks that are often described as “fuzzy” due to the ragged texture.
Small Pests That Bore and Nibble
Smaller organisms often target the internal structure or new, tender growth. The hydrangea cane borer is a significant pest whose larvae tunnel through the pith, the soft tissue inside the stem. External signs include small, round entry holes, sometimes with piles of fine sawdust, known as frass. Infested canes frequently wilt or snap easily because the internal tunneling destroys the vascular system responsible for transporting water and nutrients.
Other small pests, such as black vine weevils, cause stem and root damage. Weevil larvae feed on the root system, which can cause the stem to yellow and wilt from the top down, eventually leading to plant death. Slugs and snails are soft-bodied mollusks that typically feed on leaves, leaving ragged holes and characteristic dried slime trails. While not primarily stem-eaters, they will feed on tender new stems close to the ground.
Diagnosing Damage Based on Stem Location
Identifying the pest begins with a careful examination of the damage characteristics and height. A clean, angled cut on a stem under two feet high strongly suggests a rabbit. If the stem is ragged, torn, and shredded, especially above three feet, the culprit is almost certainly a deer. This distinction in the damage pattern is a more reliable identifier than simply the height of the wound.
Damage occurring right at the soil line, or slightly below it, points toward voles. Look for horizontal, irregular gnawing patterns that strip the bark in patches. If you observe wilting or sudden dieback on a single cane, investigate the stem for a tiny, pin-sized hole accompanied by sawdust-like frass; this is the definitive sign of a cane borer. Slugs and snails are confirmed by irregular chewing on the lowest, most tender parts of the stem and the presence of silvery, dried trails.
Actionable Steps for Pest Management
Managing large mammalian pests involves using physical barriers and repellents. For deer and rabbits, erecting a temporary fence or cage around the shrub is the most effective method of exclusion. Deer fencing should be six to eight feet tall, while rabbit fencing needs to be buried a few inches into the soil and be at least two feet high. Repellent sprays or granular products applied around the base can deter them through taste and smell aversion.
Controlling voles requires sanitation and targeted barriers. Remove excessive mulch and leaf debris from the base of the plant, as this provides them with cover. Tree guards or hardware cloth mesh placed around the base of the stems, extending above the expected snow line, prevents them from gnawing the bark. For cane borers, the only effective treatment is to prune the infected cane well below the damage until you reach solid, healthy pith tissue. The removed canes must be destroyed, not composted, and new pruning cuts can be sealed with wood glue to create a physical barrier against egg-laying adults.