Nasturtiums are popular additions to home gardens, known for their bright, funnel-shaped flowers and unique, rounded leaves. They offer both ornamental beauty in their mounding or trailing forms and culinary value, as the leaves and flowers are entirely edible. Gardeners appreciate the ease of growing these annual plants, which produce vibrant color in shades of yellow, orange, and red. A common question for anyone dealing with browsing wildlife is whether these attractive plants can withstand the appetite of deer.
The Nasturtium Resistance Verdict
Nasturtiums ( Tropaeolum majus) are widely classified as deer-resistant plants, meaning they are generally avoided by browsing deer. This aversion is primarily due to the plant’s unique chemical composition, which produces a flavor and scent deer find highly unpleasant. The plant naturally contains a high concentration of glucosinolates, which are sulfur-containing compounds. When the plant tissue is damaged, an enzyme called myrosinase converts these glucosinolates into breakdown products, most notably isothiocyanates.
These isothiocyanates are responsible for the plant’s characteristic peppery, pungent flavor and sharp aroma. This intense, mustard-like chemical defense effectively deters most deer from consuming the foliage and flowers. The resulting taste is often compared to spicy watercress or mustard greens. This flavor is simply not palatable to the majority of the deer population.
Why Deer Avoid Nasturtiums
Deer are selective foragers that rely heavily on their sense of smell to determine if a plant is worth eating. The initial, strong, and sharp odor emitted by the nasturtium acts as the primary defense mechanism, often causing the deer to pass by the plant without even tasting it. This olfactory signal essentially flags the plant as undesirable before a bite is ever taken, saving the deer from an unpleasant, peppery mouthful.
This chemical defense is distinct from physical deterrents, such as thorns or tough leaves. Nasturtiums are soft-leaved plants, making their chemical composition the sole deterrent against browsing. Deer learn through experience which plants have this strong, objectionable flavor. They typically prioritize other, less pungent food sources.
When Deer Resistance Fails
The term “deer-resistant” does not mean “deer-proof,” and there are specific circumstances where deer may overcome their natural aversion to nasturtiums. Starvation pressure is the most common factor; during periods of extreme food scarcity, such as a severe drought or harsh winter, deer will eat almost any available vegetation to survive. In these situations, the immediate need for calories outweighs the unpleasant taste of the isothiocyanates.
Newly planted or young nasturtium growth may also be more vulnerable to browsing. These tender shoots may not have developed the full concentration of defensive chemical compounds found in mature plants, making them temporarily more appealing. Local deer populations can sometimes develop different feeding habits based on the available flora in their ecosystem. If a garden offers a limited selection of food, deer may investigate the nasturtiums out of necessity.