From a botanical perspective, the term "deer resistant" is not synonymous with "deer proof." It describes a plant that possesses certain physical or chemical characteristics that make it less palatable and therefore less likely to be browsed by deer compared to more preferred forage. Deer are opportunistic feeders, and their dietary choices are influenced by availability, season, and local population pressure. A plant's resistance is a survival strategy, often involving traits like bitter tastes, toxic compounds, strong aromas, or rough textures that deter herbivory.
Black-eyed Susans (Rudbeckia hirta and other Rudbeckia species) employ several effective defensive mechanisms. Their stems and leaves are covered in small, stiff hairs (a condition known as "hirta," meaning hairy). This coarse, rough texture is unappealing to the soft mouths of deer, who tend to prefer tender, smooth foliage. More significantly, the plant contains compounds that contribute to its unpalatability. While not highly toxic, these chemical constituents can cause mild discomfort if ingested in large quantities, further encouraging deer to browse elsewhere. The combination of this physical abrasiveness and mild chemical defense places Black-eyed Susans relatively low on the list of a deer's preferred menu.
When assessing a plant's deer resistance, it is useful to compare it to known favorites and known avoidances. Deer highly favor plants like Hostas, Daylilies, Tulips, and many tender annuals which are succulent, nutrient-rich, and lack significant defensive traits. In contrast, plants that are consistently avoided, such as Lamb's Ear (Stachys byzantina) with its incredibly fuzzy leaves, or strongly aromatic herbs like Lavender and Sage, have very pronounced deterrents. Black-eyed Susans fall somewhere in the middle of this spectrum. They are not as armored as a Barberry shrub or as pungent as a Russian Sage, but they are significantly less tempting than a hybrid Tea Rose or a bed of Impatiens.
The inherent resistance of the Black-eyed Susan can be overcome by environmental circumstances. During periods of extreme drought or in late winter when preferred food sources are scarce, deer will expand their diet and may sample plants they would normally ignore, including Black-eyed Susans. This is particularly true of the younger, more tender spring growth before the stems have fully developed their characteristic hairy texture. Furthermore, a high local deer population with intense competition for resources will lead to increased browsing pressure on all available plants, testing the limits of even the most resistant species.
For a gardener, this means that while Black-eyed Susans are an excellent choice for landscapes with occasional deer pressure, they should not be relied upon as a sole deterrent in areas with a severe, chronic deer problem. Their resistance is a valuable trait that makes them a lower-risk option, but it is not an absolute guarantee. In many gardens, they will remain untouched while neighboring preferred plants are decimated. However, in times of scarcity, they may experience some browsing damage. Planting them among other resistant perennials like Coneflowers (Echinacea), Salvia, and ornamental grasses can create a garden bed that is collectively less attractive to deer.
