Asparagus is often categorized as deer-resistant, but this does not mean it is deer-proof. Deer generally avoid it when more palatable food sources are available, but resistance depends on local conditions, including deer population density and the scarcity of other forage. When natural food is limited, such as during dry summer months or in winter, deer will expand their diet to include plants they would normally ignore.
The Palatability of Asparagus to Deer
The primary reason deer tend to bypass asparagus relates to its distinctive chemical profile and physical structure. Asparagus contains various compounds, including steroidal saponins, which are naturally bitter and give the plant an unappealing flavor to many herbivores. These compounds, along with sulfur-containing carboxylic acids like asparagusic acid, contribute to the plant’s unique odor and taste, acting as a natural deterrent.
Deer are selective browsers, preferring tender, easily digestible forage, and they are quick to reject plants with strong, unpleasant tastes. This makes asparagus a low-preference food source, placing it on most lists of deer-resistant plants. The resistance level changes significantly as the plant matures through the growing season.
The young, succulent spears harvested in the spring are technically the most appealing part of the plant, but deer usually avoid them due to the intense flavor profile. Once the spears are allowed to mature into the tall, fern-like fronds, their fibrous texture adds another layer of defense. Deer find this mature growth difficult to chew and digest, making them even less likely to browse the patch unless they are facing starvation.
A patch in a suburban area with high deer pressure and limited natural food will be at greater risk than a patch with abundant alternative forage. In times of environmental stress, such as drought, deer may ignore the natural bitterness and fibrous texture simply to obtain necessary moisture and bulk.
Recognizing Deer Damage in the Asparagus Patch
Identifying deer damage rather than that caused by other common garden pests, such as rabbits or groundhogs, requires examining the height and quality of the cut. Deer lack upper incisors, meaning they cannot make a clean bite through a stem. When a deer feeds on a spear or fern, they clamp down with their lower teeth against a hard dental pad and then rip or jerk the plant material away. This action leaves a characteristic ragged or torn edge on the remaining stem, which is the most reliable indicator of deer browsing.
In contrast, rabbits and woodchucks have sharp incisors that leave a clean, angled cut, similar to a precise snip with shears. Deer damage usually occurs between one and six feet off the ground, corresponding to their natural browsing height, while rabbit damage is typically confined to the lowest few inches of the plant.
Further evidence can be found in the immediate vicinity of the damage, particularly the presence of tracks and droppings. Deer leave distinct triangular-shaped hoof prints, and their elongated, pellet-like droppings may be scattered nearby. Since deer activity is often nocturnal, inspecting the patch early in the morning for these signs helps confirm the culprit before implementing protective measures.
Effective Strategies for Protecting Asparagus
The most reliable method for protecting an asparagus patch from persistent deer browsing is the installation of physical barriers. Because deer can clear considerable heights when motivated, an exclusion fence must be at least eight feet tall to be consistently effective. This height prevents the deer from feeling secure enough to attempt a jump over the barrier.
Where a full eight-foot fence is impractical, alternative barrier designs can be used to confuse the deer’s depth perception. A double-fence system, consisting of two parallel fences about four to five feet apart and only five feet high, can be surprisingly effective. Deer are reluctant to jump a barrier if they cannot clearly see a safe landing area on the other side.
Repellents offer a secondary defense and are categorized as either taste-based or scent-based deterrents. Scent-based products, often containing ingredients like putrescent egg solids, work by mimicking the smell of predators or decay, signaling danger to the deer. Taste-based repellents are applied directly to the foliage and make the asparagus unpalatable, reinforcing the plant’s natural bitterness.
To prevent deer from becoming accustomed to a single defense mechanism, it is important to rotate between different types of repellents every few weeks. Applying these products consistently, especially during times of highest risk such as drought or early spring growth, maximizes their effectiveness, and planting asparagus away from known deer travel corridors or near the house can also help.