The salvia plants in the author's garden are pleasing to humans, but their scent is not attractive to deer and other herbivores.
Photo: Marie Lane Gewecke
Marie Lane Gewecke
Photo by Nikki Moore
Most of us have to consider resistance to predation by wildlife when choosing new plants for our gardens. Deer, rabbits, and favorite tunneling animals can all wreak havoc in a garden. Many gardeners put up fences around their plants, spray repellents, or take other measures to keep herbivores (wild animals that eat plant tissue) at bay.
While animals can escape predators, plants are sessile, meaning they're permanently attached to a base and can't move around. Because they're anchored by their roots, many plants have developed defenses to protect themselves. Some emit unpleasant odors, some are armed with painful thorns, and some are poisonous.
Aromatic plants not only deter herbivores from eating them, but some have such strong smells that they protect plants nearby. Hungry animals may smell it and avoid the area. Artemisia “Seafoam” has a sage scent. Humans may find it pleasant or at least not mind the smell, but it effectively repels animals. Similarly, aromatic aster (Symphyotrichum oblongifolium) “October Sky” leaves, when rubbed, release a balsam scent. Again, this is acceptable to humans but repels deer and rabbits. Other perennials to consider include yarrow, salvia, catmint, bee balm, lavender, and Russian sage.
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Thorns, spines, prickly plants, and sometimes tough leaves, keep gatherers (and sometimes humans) away. Hawthorn and honey locust trees both have terrible thorns. Prickly pear, barberry, nettle, and American holly have sticky thorns. Roses, contrary to popular belief, have prickles, not thorns. Regardless of what their pointed protuberances are called, a sting is painful. Even the prickly cones of the coneflower (echinacea) seem to keep deer away. Ligularia plants have thick, serrated leaves that are difficult to chew.
Some plants have chemical defenses that make them at least taste bad, while others are poisonous. Plants with chemical defenses include Digitalis obscura (Digitalis spp.), Aconite (Monkshood spp.), milkweed, and the green immature stages of nightshade plants. Poisonous plants are dangerous to predators as well as children and pets, and should be used with caution.
Houseplants also have defenses. The dieffenbachia defense mechanism is invisible and odorless, but it has calcium oxalate crystals in its leaves. When released, the crystals release an enzyme that is toxic if ingested and can cause paralysis and speech impediments. That's why the plant is called “dumb cane.” Houseplants that contain similar chemicals include caladiums, Chinese evergreens, philodendrons, and pothos (Epipremnum aureum).
As gardeners, we might consider using some of these natural weapons as defenses against herbivore swarms. Remember to use longer, sturdier gardening gloves and long-handled pruning shears when working with these plants.
Mari Lane Gewecke has been a Master Gardener volunteer with the University of Nebraska-Lincoln Campus Program since 2004. She is a semi-retired philanthropy consultant.
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