Black-Eyed Susans (Rudbeckia) are popular garden plants known for their bright appearance and resilience. They are typically classified as deer-resistant, meaning they are generally unappealing and not a preferred food source. However, gardeners must understand that “deer resistant” does not equate to “deer proof.”
Why Deer Avoid Black-Eyed Susans
The natural defenses of Rudbeckia plants rely on physical texture and unpalatable chemistry. Mature Black-Eyed Susan stems and leaves, especially Rudbeckia hirta, are covered in tiny, stiff hairs called pubescence. This rough, fuzzy texture is physically unappealing to a deer’s sensitive mouth, making the plant difficult to chew.
The plant also contains bitter-tasting secondary compounds, such as phenolic acids and flavonoids, which serve as chemical defenses. These compounds accumulate in the foliage and stems, creating an unpalatable taste that deer instinctively avoid. These compounds interfere with digestion, leading to reduced nutrient absorption and discomfort.
This combination of a rough surface and bitter flavor guides deer to select more palatable plants instead. Consequently, Black-Eyed Susans are rated by extension services as seldom or rarely damaged.
Situations Where Deer Might Still Browse
Despite their defenses, specific environmental conditions can override a deer’s natural aversion. Extreme hunger or food scarcity, such as during drought or harsh winter conditions, is the most significant factor. When preferred food sources are unavailable, deer are compelled to consume plants they would normally ignore simply to survive.
High local population density also increases competition for food. In areas with intense browsing pressure, deer are more likely to sample a wider range of vegetation, including less desirable Rudbeckia species.
The age of the plant affects its vulnerability, as young growth is often more tender and lacks the full defensive profile of a mature specimen. Seedlings and newly emerging leaves are susceptible to browsing before the rough texture and bitter compounds fully develop.
Practical Steps for Garden Protection
For gardeners in areas with high deer activity, proactive measures can significantly reduce the risk of browsing.
Repellents
One strategy is using repellents, available in granular or spray formulations, which create a bad taste and an offensive smell. These products must be reapplied after heavy rainfall or when new growth emerges to maintain effectiveness.
Physical Barriers
Physical protection is effective, especially for vulnerable new plantings. Grow seedlings in pots until they reach at least six inches to develop tougher foliage before planting. Temporary caging or netting can safeguard individual plants until they are established.
Companion Planting
Companion planting uses aromatic species to deter deer. Planting highly fragrant, unpalatable plants, such as lavender or yarrow, near the Black-Eyed Susans creates a “confusion effect.” This masks the scent of the Rudbeckia, making it harder for deer to locate the flowers.