Hyssop, a perennial herb valued for its aromatic foliage and attractive flower spikes, is often sought after by gardeners looking to introduce color and pollinators without attracting unwanted browsing animals. The question of whether this plant is safe from deer is a common one, especially in areas where deer populations are high and garden damage is a regular concern. Hyssop is largely considered highly resistant to deer, making it a reliable choice for planting along borders or in mixed beds, but this resistance is not absolute. Understanding the plant’s natural defenses and the environmental pressures that can affect deer behavior is the best way to utilize hyssop effectively in the landscape.
Hyssop’s Natural Defense Mechanism
Hyssop’s strong resistance to deer browsing stems from its concentration of powerful aromatic compounds. The plant’s leaves and stems are rich in essential oils, which are primarily a mixture of chemical compounds known as terpenoids. Deer rely heavily on their sense of smell to identify food, and these intense, pungent aromas are highly unappealing to them.
In Hyssopus officinalis, or true hyssop, the essential oil profile includes significant levels of ketones, such as pinocamphone. This particular compound contributes to the herb’s strong, somewhat camphorous scent, which deer find irritating and unpalatable, causing them to move on to less offensive forage. The taste of these oils is also bitter, serving as a secondary deterrent once a deer takes an initial, tentative bite.
Physical characteristics also contribute to the plant’s defense. Hyssop typically develops a somewhat woody stem and has a slightly coarse texture. These features make the plant less tender and less desirable than soft, succulent foliage, further discouraging browsing by large herbivores. The combination of strong scent, bitter taste, and textural toughness creates a highly effective natural barrier against most deer.
Variations in Resistance Among Hyssop Types
When discussing hyssop, it is important to distinguish between the two main types used in gardens, as they possess slightly different resistance profiles. True Hyssop (Hyssopus officinalis) is the classic variety, known for its intense, herbaceous, and slightly medicinal fragrance. This species is almost universally avoided by deer due to its high concentration of defensive chemical compounds.
The second common type is Anise Hyssop, which belongs to the genus Agastache and is botanically distinct from true hyssop. Agastache species are also highly deer-resistant, but their scent profile is different, often described as licorice or anise-like. This difference in scent is due to varying essential oil compositions, though both contain strong aromatic terpenoids that repel deer.
Rutgers University, which rates landscape plants for deer resistance, often places both Hyssopus and Agastache in the “Rarely Damaged” category. While both are excellent choices, some anecdotal reports suggest that in low-pressure environments, a curious deer might sample the milder, sweeter-scented Anise Hyssop more readily than the strongly camphorous True Hyssop. However, any browsing damage to either variety is usually minimal and quickly abandoned.
Environmental Factors That Override Resistance
While hyssop is highly resistant, no plant is entirely “deer-proof,” and environmental factors can override a deer’s natural aversion.
Nutritional Stress
The primary factor is extreme nutritional stress, which occurs when a deer faces a severe shortage of preferred food sources. During periods of drought, deep snow cover, or late winter when other forage is scarce, a starving deer may reluctantly browse on plants it would normally ignore.
High Deer Density
High local deer density also plays a significant role in overriding resistance. In areas where the deer population exceeds the available natural food supply, competition and hunger force the animals to expand their diet to include less palatable plants. Even a strong scent like hyssop’s may be overlooked when a deer is desperate for calories.
Plant Maturity
The maturity of the plant can also influence whether it is browsed. Young, newly planted hyssop or the fresh, tender growth that emerges early in the season often contains lower concentrations of the bitter essential oils. This softer tissue is more vulnerable to being sampled or damaged than the tough, mature foliage and woody stems of an established plant. Planting hyssop near other, more attractive plants may also lead to accidental browsing.