Cosmos are popular annual flowers, cherished for their delicate, daisy-like blooms and feathery foliage. Gardeners often seek out these flowers but frequently wonder if they will survive the local deer population. Cosmos are generally considered highly deer-resistant, meaning they are rarely a preferred food source for browsing animals. This natural resistance provides a significant advantage for gardeners in areas with high deer activity.
Why Deer Tend to Avoid Cosmos
Deer rely heavily on their sensitive sense of smell and taste to select their forage. The foliage of the cosmos plant possesses a strong, somewhat pungent aroma that deer find unappealing compared to more palatable plants.
The plant’s resistance is supported by the texture and chemical makeup of its leaves. Many varieties of cosmos have slightly fuzzy or hairy foliage, a texture that deer dislike because it is uncomfortable to chew. Additionally, the plant contains specific chemical compounds that give it a bitter or unpalatable taste, acting as a defense mechanism against browsing. For a deer, the combination of strong scent, bitter flavor, and undesirable texture makes cosmos a low-priority food source.
Environmental Factors that Increase Browsing
While cosmos possesses natural defenses, no plant is entirely safe from a hungry deer. Exceptions to their resistance occur when environmental pressures reduce the availability of preferred forage. During periods of extreme scarcity, such as severe drought or deep winter snow, deer become significantly less selective about what they consume.
High deer population density in a localized area can also increase browsing pressure on less desirable plants like cosmos. Increased competition forces deer to consume nearly any available plant matter, even those normally avoided. Young cosmos seedlings and new growth are particularly vulnerable, as the tender new foliage is softer and contains lower concentrations of the bitter-tasting defense compounds than mature plants.
Protecting Your Cosmos from Hungry Deer
If deer are browsing your cosmos, gardeners should employ a multi-faceted approach combining repellents and physical barriers. Repellents fall into two main categories: taste-based and scent-based formulas. These should be applied directly to the plants and rotated occasionally to prevent deer from becoming accustomed to a single deterrent. Taste repellents render the foliage unappetizing, while scent repellents use foul odors, such as rotten eggs or garlic, to deter foraging. These applications must be reapplied frequently, particularly after heavy rain or new plant growth.
Physical exclusion is the most reliable method, especially for protecting young plants. Temporary cages or woven-wire cylinders can be placed around individual cosmos during their most vulnerable stage. For a larger garden area, a permanent fence should be at least eight feet high, as deer are capable of jumping lower barriers when motivated. Using highly fragrant companion plants, such as lavender, mint, or sage, near the cosmos can also help mask their presence and confuse the deer’s acute sense of smell.