Lilac trees (Syringa vulgaris and related species) are common flowering shrubs valued for their fragrant blooms across North American landscapes. For homeowners in areas with high deer populations, the potential for browsing damage is a recurring concern. Lilacs are generally categorized as a species that deer tend to avoid, but this resistance is not absolute.
Lilac Resistance: Status and Mechanism
Lilacs are widely considered deer-resistant, meaning they are not a preferred food source compared to many other garden plants. This natural avoidance stems from the plant’s unique biological makeup, which includes volatile compounds in the leaves and stems. These compounds are secondary metabolites that plants produce as a natural deterrent against herbivores.
The strong, distinctive fragrance of the lilac foliage acts as a sensory repellent, making the plant less appealing to a deer’s sensitive sense of smell. If a deer attempts to browse, the leaves contain phenolic compounds and terpenes that contribute a bitter taste. This combination of undesirable scent and flavor causes deer to typically move on to forage on more palatable vegetation, resulting in lilacs being rated as “seldom severely damaged” in deer resistance scales.
Factors That Compromise Resistance
While lilacs are not a favorite food, “deer-resistant” is not synonymous with “deer-proof,” and damage can still occur under certain conditions. The primary factor that overrides a deer’s natural aversion is extreme hunger or scarcity of preferred food sources. During periods of severe drought, heavy snow cover, or overpopulation, the pressure to find nourishment can compel deer to browse on plants they would normally ignore.
The plant’s life stage also plays a significant role in its vulnerability. The tender, new shoots and buds that emerge in early spring have lower concentrations of bitter compounds and are more palatable to hungry deer. Newly planted or young shrubs are easier targets and may be browsed as deer explore new food items. Additionally, damage may not always be from feeding; male deer sometimes rub their antlers on the bark of young lilac trunks to remove velvet or mark territory, which can severely injure or girdle the plant.
Practical Protection Strategies
For gardeners who experience browsing damage, implementing practical measures can significantly reduce the risk of harm. The most reliable method involves installing a physical barrier, such as a sturdy fence that is at least seven to eight feet tall to prevent deer from jumping over it. For individual shrubs, temporary enclosures made of wire mesh or netting should be secured to the ground so deer cannot nudge underneath.
Chemical repellents offer a secondary layer of protection by making the plant less appealing to the deer’s senses. These products are categorized as either odor-based, which use a strong smell to deter approach, or taste-based, which contain ingredients like putrescent egg solids or capsaicin to create an unpleasant flavor. Repellents must be reapplied frequently, especially after heavy rain or during periods of rapid new growth in the spring, to maintain their effectiveness.
Another strategy involves using sensory deterrents, such as motion-activated sprinklers. These deliver a sudden burst of water when a deer enters the protected area, conditioning the deer to avoid the location over time. Protecting new growth is particularly important, so focus efforts in the early spring and throughout the first year after planting to help the lilac establish itself and minimize the chances of damage. Protecting the trunk of young trees with corrugated pipe or tree wrap also prevents antler rubbing damage during the fall and winter.