Nasturtiums, known scientifically as Tropaeolum majus, are popular, easy-to-grow annuals prized by gardeners for their vibrant, funnel-shaped flowers and attractive, rounded leaves. Every part of the plant—from the flowers to the seeds and foliage—is edible for humans. However, the presence of deer often introduces a complication for gardeners hoping to incorporate these colorful plants into their landscape. The central question for many is whether these annuals can withstand the persistent browsing pressure from local deer populations. Nasturtiums are frequently listed among plants that deer tend to avoid, but this resistance is not universally guaranteed.
The Nasturtium Deer Paradox
The general resistance of nasturtiums to deer browsing is rooted in the plant’s distinct chemical defense system. Nasturtiums, like many members of the cabbage family, are rich in compounds called glucosinolates.
When a deer takes a bite, specialized enzymes are released, which rapidly convert the glucosinolates. This reaction converts the compound into a strong, volatile substance known as a mustard oil, or isothiocyanate, which creates a sharp, peppery, and unpleasant flavor. Deer tend to learn quickly and avoid plants that produce this intense taste. This defense mechanism is why nasturtiums are classified as deer-resistant.
This inherent chemical protection, however, is not absolute, creating a paradox for gardeners who still see damage. While deer generally reject the strong flavor, they are also opportunistic foragers driven by nutritional needs. A young or inexperienced deer may sample the plant out of curiosity before learning to avoid it. The plant’s internal chemistry provides a strong deterrent, but this natural defense can be overcome by external pressures.
Situational Variables Influencing Browsing
Environmental conditions and population dynamics are external factors that can override the nasturtium’s chemical defenses. When natural food sources become scarce, such as during periods of extreme drought or late winter, deer become less selective in their foraging. A deer facing starvation may choose to consume a less palatable plant like nasturtium rather than go hungry.
The density of the local deer population also plays a role in browsing behavior. In areas with high deer density, the competition for preferred forage increases, leading deer to expand their diet to include plants they would normally ignore. This competition-driven expansion can push them to consume even plants with strong deterrents. Environmental factors greatly influence the availability and quality of forage, forcing deer to browse on plants they might otherwise leave alone. Even though nasturtiums are not a favored food, the combination of a high deer population and limited alternative food can make them a target of last resort.
Practical Strategies for Plant Protection
Gardeners in areas with sustained deer pressure can implement several strategies to supplement the nasturtium’s natural resistance.
Physical Barriers
Physical barriers offer the most reliable form of protection, especially for new or vulnerable plantings. Temporary netting or small wire cages placed around newly planted nasturtiums prevent deer from getting a taste early on. This allows the plants to establish themselves.
Repellents
Repellents provide another layer of defense, working through either taste or scent to discourage browsing. Taste-based repellents contain ingredients that are unpalatable but harmless, while scent-based products use strong, unfamiliar odors to alarm the deer. The effectiveness of any repellent is dependent on consistent reapplication, particularly after rain or heavy dew, as the active ingredients wash away.
Companion Planting
Incorporating companion planting can also increase the overall deterrent effect in the garden. Placing nasturtiums adjacent to other highly aromatic, deer-resistant herbs, such as rosemary or sage, creates a combined odor barrier. This strategy uses the strong smell of the companion plants to reinforce the deterrent qualities of the nasturtiums. Some gardeners also use motion-activated sprinklers, which startle the deer with a sudden burst of water, to effectively change their grazing path.