Courtesy Marie Coleman/Flickr
One aspect of companion planting that can be quite useful in the vegetable patch is partnering plants in hopes of repelling certain pests. While many pest-deterring companion planting tactics have yet to be scientifically proven, there's no doubt that several of them are quite effective in deterring certain pests in the garden, even if they've only been "proven" via hand-me-down knowledge. Even if a particular pest-deterring plant partnership doesn't work in your garden, it certainly won't cause it any harm.
Here are a handful of my favorite plants for discouraging pests in the vegetable garden to jumpstart your companion planting endeavors.
Among the most popular partnerships, basil and tomatoes go hand-in-hand—both on the plate and in the garden. Basil is said to repel whiteflies, spider mites and aphids on tomatoes. Planting basil around young tomato plants can confuse adult hornworm moths, preventing them from finding the plants and laying their eggs.
Dill helps deter squash bugs, so plant it among your squash plants to keep your crop safe. It also helps repel adult cabbageworms when planted among cabbage and other cole crops. The heavily scented leaves of dill may repel other insects, as well, or simply mask the scent of the host plant.
Many gardeners find success planting nasturtiums among cucumber vines to repel the cucumber beetles that feed on cucumber leaves and flowers, and transmit bacterial wilt. Some gardeners also report that vining nasturtium varieties help deter squash bugs when planted among winter squash.
The bold odor of onions may actually repel pests or confuse them by masking the fragrance of their preferred host plants. Either way, onions in the cucumber patch can scare off cucumber beetles, and planting them between carrot rows repels adult carrot root maggot flies. Circling a row of onions around tomato plants is also said to help repel sap-sucking aphids.
The scent of this aromatic is said to repel aphids in the lettuce patch, as well as send Japanese beetles packing when planted around blueberries, roses, raspberries and other susceptible crops. Garlic plants are also used to keep spider mites away from phlox and other vulnerable perennials.
With strongly scented foliage of their own, many gardeners use tomatoes to protect their cabbage and broccoli crop from diamond back moth larvae. The adult moths are less likely to lay eggs on cole crops planted between and beneath tomato plants.
7. Catnip (Nepeta spp.)
Plant this perennial member of the mint family between rows of plants susceptible to flea beetle damage, such as radish and eggplants, as the adult beetles are repelled by the fragrance.
Another member of the mint family, this perennial is reportedly quite adept at deterring cabbageworms, cabbage loopers and diamondback moth larvae on cole crops. Plant a few calamint plants near these crops, but be careful to deadhead the flowers before they drop seed to prevent it from taking over the garden.
Some gardeners use this herb to keep Japanese beetles at bay, planting it among brambles, roses and other plants favored by adult Japanese beetles. Tansy's strong scent is said to either deter them directly or make it difficult for the beetles to hone in on their host plant.
Tall marigold varieties, such as African marigolds (Tagetes erecta), are used by some gardeners to deter tomato and tobacco hornworms. When planted in between tomato plants, they are thought to confuse the adult hornworm moths and keep them at bay.
Used by gardeners for centuries to discourage hornworms on tomatoes and cabbageworms on cole crops, borage is a beautiful addition to the garden. Easily grown from seed, this herb can be readily grown around susceptible plants. It's also great at supporting Honey bees and other pollinators.
When grown among lettuce and other leaf crops, the heavily scented leaves of lavender dissuade both whiteflies and aphids.
Planting parsley in the asparagus bed may send asparagus beetles packing, particularly early in the season when the spears are just emerging.
14. Castor Oil Plant
Although it should be grown with care (all parts—especially the beans—are extremely poisonous to humans and animals when ingested), the castor oil plant is proven to keep moles and voles at bay. Planted around the perimeter of the garden, it keeps voles from moving in. Some commercial mole and vole repellents are even made from the castor oil plant because it works so well.
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About the Author: Horticulturalist Jessica Walliser is the author of Good Bug, Bad Bug: Who's Who, What They Do and How to Manage Them Organically (St. Lynn's Press, 2008) and co-host of Pittsburgh's top-rated gardening radio program, The Organic Gardeners, on KDKA Radio. Learn more helpful gardening tips in her blog, "Dirt on Gardening."