Yarrow (Achillea millefolium) is a flowering perennial native to temperate regions across the Northern Hemisphere, commonly cultivated for its feathery foliage and flat-topped clusters of small flowers. This resilient plant thrives in various conditions, offers a long blooming season, and attracts beneficial insects. Yarrow is notably deer-resistant, making it a preferred choice for landscapes where deer browsing is a frequent concern.
Yarrow’s General Resistance to Deer Browsing
Yarrow is consistently categorized by horticultural experts and university extension offices as a low-preference food source for deer, meaning they seldom cause severe damage. The plant’s structure and texture contribute significantly to its low palatability, making it mechanically difficult for deer to consume. Deer typically favor plants with soft, smooth, and succulent leaves, which contrasts sharply with yarrow’s physical attributes.
The stems and foliage of mature yarrow are noticeably coarse and fibrous, presenting a challenging texture to browsing animals. Its finely cut, fern-like leaves possess a slightly hairy or fuzzy surface, which deer generally find unappealing. Deer are browsing animals that prefer to tear off soft material rather than chew through rough, fibrous matter, contributing to yarrow’s reputation as a reliable deer-resistant perennial.
The Aromatic Compounds That Deter Deer
The primary defense mechanism of yarrow lies in its unique chemical composition, which produces both a strong odor and a bitter taste that deer actively avoid. Yarrow foliage contains high concentrations of volatile organic compounds (essential oils), responsible for its pungent, herbal aroma. Deer rely heavily on their sense of smell to identify food, and this strong scent acts as an immediate chemical warning signal.
Upon being crushed or chewed, the plant releases these aromatic compounds, immediately signaling to the deer that the food is undesirable. The plant also contains complex secondary metabolites, including phenolic compounds and flavonoids, which impart a distinctly bitter taste. Ingesting these compounds can be unpalatable or mildly toxic to deer, creating an unpleasant post-ingestion experience that reinforces their natural avoidance behavior. This chemical deterrent is often released in higher concentrations in the mature plant.
Environmental Factors Leading to Yarrow Consumption
While yarrow is highly resistant, deer will sometimes consume it under specific external pressures. The most common cause is extreme food scarcity, typically occurring during harsh winter months or periods of severe drought. When preferred food sources are unavailable, deer become opportunistic and may resort to eating less palatable plants simply for survival.
High deer population density also increases browsing pressure, forcing animals to feed on plants they would normally ignore. The age of the plant material is also a factor, as the young, tender shoots that emerge in early spring have not yet developed the maximum concentration of deterrent essential oils and fibrous texture. These soft growths are occasionally sampled by deer before the plant’s full chemical and physical defenses are established.