Gardening: Plants that protect themselves

For most of us, resistance to predation by wildlife must be considered when choosing new plants for the landscape. Deer, rabbits and your favorite choice of tunneling creature – all can wreak havoc in the garden. Many gardeners will place fences around their plants, douse them with deterrents or take other actions to discourage herbivores (wildlife that ingest plant tissue).

While an animal can run away from a predator, a plant is sessile, meaning it is permanently attached at the base and cannot move about. With roots anchoring them in place, many plants have developed defenses to protect themselves. Some plants produce an unpleasant odor; others arm themselves with painful spikes and still others are toxic.

Odiferous plants not only deter herbivores from eating them, but some have a strong enough odor to protect other plants nearby. Hungry critters may just avoid the area once they get a whiff. Artemisia ‘Sea Foam’ has the aroma of sage. Humans may find it pleasant or at least don’t mind the smell but it effectively deters critters. Similarly, when rubbed, the leaves of aromatic aster (Symphyotrichum oblongifolium) ‘October skies” release a balsam scent, again something humans can accept but repels deer and rabbits. A few other perennials to consider are yarrow, salvia, catmint, bee balm, lavender and Russian sage.

Plants with thorns, spines or prickles – and sometimes tough leaves – discourage foragers (and, occasionally, people). Both hawthorn and honeylocust trees have wicked thorns. Plains prickly pear, barberry, stinging nettle and American holly have sticky spines. Roses – contrary to popular belief – do not have thorns; they have prickles. Regardless of what those pointy protrusions are called, they hurt when they poke. Even the spiky cones of coneflower (Echinacea) seem to deter deer. Ligularia plants have serrated foliage that is thick and tough to chew.

Some plants have chemical defenses which, at the very least, taste bad; others are toxic. Plants with chemical defenses include Digitalis obscura (foxglove), monkshood (genus Aconitum), milkweed and the green immature stage of nightshade. Toxic plants are dangerous to not only their predators but children and pets. They should be used with caution.

Even houseplants can have defenses. While you may not see or smell the defense mechanism in dieffenbachia, inside its leaves are calcium oxalate crystals. When released, the crystals deliver an enzyme that is venomous if ingested; it can cause paralysis and/or speech impairment. Hence, its common name: dumb cane. Other houseplants with similar chemicals include caladium, Chinese evergreen, philodendron and pothos (Epipremnum aureum).

As gardeners, we might consider employing some of these natural weapons as defense against the herbivore horde. Remember to use longer, tougher gardening gloves and a long-handled pruner when working with some of these plants.