From a botanical perspective, the primary reason peonies (genus Paeonia) are often considered deer-resistant lies in their chemical composition. Peonies contain compounds that are unpalatable and potentially toxic to deer and other herbivores. Specifically, they contain paeonol, a compound found in the bark of the peony root, which is used in traditional medicine but acts as a natural deterrent to grazing animals. Furthermore, like many plants that have evolved defenses, peonies likely contain additional secondary metabolites such as tannins and alkaloids that make their foliage and flowers taste bitter and unpleasant. When a deer samples a peony, it quickly learns that the plant is not a desirable food source. This built-in chemical defense system is the most significant factor contributing to the peony's resilience against deer browsing.
Beyond their chemical defenses, peonies possess certain physical attributes that deer find unappealing. While not as formidable as the thorns on a rose bush, the texture and structure of the peony plant play a role. The stems are sturdy and somewhat woody, and the large, leathery leaves are not the tender, succulent foliage that deer prefer. Deer typically seek out plants with soft, non-fibrous leaves that are easy to digest. The substantial, often glossy leaves of the peony do not meet this criteria. Additionally, the complex, densely-packed petals of the double-flowered varieties create a texture that is likely confusing and undesirable for a deer's palate compared to simpler, more accessible flowers or foliage.
It is crucial to understand the distinction between "deer-resistant" and "deer-proof." A peony's defenses are not an impenetrable shield; they are a deterrent. A plant's ability to repel deer is highly situational and can vary based on external pressures. During times of extreme scarcity, such as a harsh winter with deep snow cover or a prolonged drought, deer populations become desperate for any available food source. Under these conditions, a deer's survival instinct will override its aversion to bitter tastes and tough textures. A hungry deer will eat plants it would normally avoid, including peonies. Therefore, while peonies are low on the list of preferred browse, they are not immune to being eaten when alternative food is unavailable.
From the plant's developmental standpoint, not all parts of a peony are equally defended at all times. New, emerging shoots in the spring are particularly vulnerable. These young shoots are more tender and contain slightly different concentrations of chemical deterrents compared to the mature plant. A deer might nip off these fresh buds before they have fully developed their characteristic bitterness. Similarly, the flower buds themselves can be a target. While the open flower with its strong fragrance (a sign of its volatile compounds) is a clear deterrent, a tightly closed bud might be sampled out of curiosity. It is also worth noting that while the foliage and flowers are protected, deer do not dig for roots, so the plant's underground tubers are safe from this particular threat, allowing the plant to survive and regrow even if the above-ground parts are damaged.
To support the peony's inherent deer resistance, gardeners can employ strategies that work in concert with the plant's biology. Planting peonies alongside other strongly-scented deer-resistant plants like lavender, sage, or catmint can create a sensory barrier. The powerful aromatic compounds from these companion plants can help to mask the scent of any tender new peony growth. For times of high deer pressure, such as the early spring when shoots are vulnerable, physical protection is the most reliable method. Using deer netting or repellent sprays can provide an additional layer of security. Repellents work by introducing smells or tastes (like putrescent egg solids or capsaicin) that are even more offensive to deer than the peony's natural defenses, effectively reinforcing the plant's own survival strategy.
