Coleus, a genus of plants prized for its vibrantly colored and patterned foliage, is a popular ornamental choice for shady garden spaces. Gardeners often select it because the plant is widely considered resistant to browsing by common mammalian pests like deer and rabbits. This resistance is not a guarantee of total immunity but rather an indication that the plant is not a preferred food source. The degree of protection varies based on a few distinct factors.
Deer Resistance: The Taste and Smell Factors
Deer largely avoid Coleus due to its chemical composition, which renders the plant unpalatable. Like many members of the mint family (Lamiaceae), Coleus contains aromatic essential oils and bitter-tasting compounds. Deer rely heavily on their sense of smell and are immediately deterred by the strong, distinct scent profile of the foliage.
The plant’s defense mechanism includes secondary metabolites that act as a natural deterrent, signaling that the plant is disagreeable to eat. While a deer may sample a leaf, the immediate bitter flavor discourages further browsing. This combination of strong odor and off-putting taste is effective in protecting the plant from significant damage.
Rabbit Resistance: Ground-Level Foraging
Rabbits, much like deer, are repelled by the chemical defense system Coleus employs, which is effective against ground-level foragers. Their reaction to the Coleus’s bitter taste and strong odor is similar to that of deer, making it an undesirable food source.
A rabbit’s foraging behavior involves clipping plants close to the ground, making them destructive to new or tender growth. However, the plant’s inherent bitterness usually results in the rabbit moving on quickly after an initial nibble. They still prioritize plants that lack these strong, defensive flavors.
Contextualizing Resistance: When Coleus Is Still Eaten
The term “resistant” does not mean a plant is immune to being eaten. Coleus resistance can be overcome by environmental pressures, particularly when a lack of alternative food sources occurs. During periods of drought or deep winter when preferred forage is scarce, deer and rabbits may resort to eating plants they would normally avoid.
The plant’s age can also influence its palatability, as very young or newly established Coleus plants may not have fully developed the concentration of chemical deterrents found in mature foliage. High populations of deer or rabbits in a localized area can also lead to increased browsing pressure, forcing them to consume less desirable plants. Localized feeding habits can also vary, as an individual animal that has already sampled and tolerated Coleus is more likely to eat it again.
Protecting Coleus from Non-Mammalian Pests
Since Coleus is often safe from large herbivores, gardeners should focus on managing smaller, non-mammalian threats that can cause significant damage. The plant is susceptible to sap-sucking insects, including aphids, mealybugs, and whiteflies, which extract nutrients and weaken the plant. Mealybugs appear as fuzzy, white masses, while aphids cluster on new growth, often leaving behind sticky honeydew.
Fungal diseases are also a common concern, with Downy Mildew and root rot being prevalent issues. Downy Mildew manifests as irregular brown lesions on leaves and thrives in high humidity. To combat these threats, ensure proper air circulation and avoid overhead watering, which can spread fungal spores. Insect pests can often be controlled with insecticidal soap or by wiping them off with rubbing alcohol.