Ageratum, commonly known as Floss Flower, is a popular bedding plant prized for its fluffy, pom-pom-like blooms in shades of blue, purple, and white. Cultivated as an annual in cooler climates, it functions as a tender perennial in frost-free regions. Ageratum is widely considered deer resistant, meaning it is typically avoided by deer but is not entirely deer proof. This distinction is important, as the plant possesses natural defense mechanisms that make it unappealing to browsing animals.
Ageratum’s Status as a Deterrent Plant
The plant’s natural resistance is rooted in a combination of taste, scent, and texture that discourages browsing deer. Many varieties of Ageratum, particularly Ageratum houstonianum, feature leaves with a slightly hairy texture. This fuzzy surface acts as a mechanical deterrent, making the foliage physically unpleasant for deer to chew.
The primary defense lies in the plant’s internal chemistry, which produces a distinctly bitter taste. Ageratum contains pyrrolizidine alkaloids, responsible for this unappealing flavor. These alkaloids are known to be toxic to grazing animals, specifically causing liver lesions if consumed in large quantities. Deer can detect and avoid such bitter, potentially harmful substances, making Ageratum a low-priority food source. The resulting pungent scent and bitter flavor act as a chemical warning sign, convincing the animal to move on. This inherent defense is why the plant is consistently featured on lists of deer-resistant annuals.
External Factors That Decrease Resistance
The effectiveness of Ageratum’s natural defenses can be overcome by certain environmental pressures. The most common factor leading to browsing is high deer pressure, where starving animals will consume almost any vegetation, regardless of taste or texture. When food scarcity is severe, the risk of eating a bitter plant is outweighed by the immediate need for calories.
Young, tender growth is also more vulnerable than mature plants because it often contains lower concentrations of the bitter pyrrolizidine alkaloids. New leaves may also lack the fully developed hairy texture of mature foliage. Deer may test-browse these young shoots before moving on.
Specific cultivars can also exhibit varying degrees of resistance. Highly hybridized varieties, bred primarily for flower color and extended bloom time, may have had their natural chemical concentrations inadvertently reduced. Environmental stress, such as prolonged drought, can sometimes alter the plant’s chemical composition, affecting the intensity of its bitter compounds.
Maximizing Protection Through Garden Placement
Gardeners can enhance Ageratum’s deterrent properties through strategic placement in the landscape. Planting Ageratum as a border or edging plant creates a protective barrier around more favored, non-resistant species. This companion planting technique forces deer to encounter the bitter foliage before reaching desirable plants.
Positioning Ageratum near high-traffic areas, such as walkways, patios, or close to the home, also utilizes the deer’s natural aversion to human activity. Deer are less likely to linger and browse in spots where they frequently perceive human presence or noise.
Maintaining the plant’s health is another way to support its resistance. Ensuring the Ageratum receives adequate water and nutrients helps it maintain the vigorous growth and chemical integrity necessary for a strong alkaloid concentration.