Garden Q&A: 'Proven' pest-deterring plants
Question: I've heard that there are certain plants you can plant in your garden to help deter pests. Is there any truth in that, or is it just a bunch of old wives' tales?
Answer: The technique of partnering certain plants with others in hopes of deterring certain pests is a type of companion planting. While many pest-deterring companion planting tactics are not scientifically proven, there's no doubt that some partnerships work, even if they've only been “proven” via hand-me-down knowledge.
While it's true that some companion planting pairings may be more effective than others when it comes to deterring pests, they are worth trying because even if a particular pest-deterring plant partnership doesn't work as well as you'd hoped, it certainly won't cause it any harm. Here are a few of my favorite combinations.
Basil: Among the most popular partnerships, basil and tomatoes go hand in hand — both on the plate and in the garden. Basil is purported to repel whiteflies, spider mites and aphids on tomatoes. Planting basil around young tomato plants also may confuse adult hornworm moths, preventing them from finding the plants and laying their eggs.
Dill: When planted in the squash patch, dill may deter squash bugs. It also may help repel adult cabbageworms when planted amongst cabbage and other cole crops. The heavily scented leaves of dill may repel certain insects, or it may serve to mask the scent of the host plants.
Nasturtiums: Success is found by many gardeners when planting nasturtiums among cucumber vines. They are reported to repel the cucumber beetles that often feed on cucumber leaves and flowers, and transmit bacterial wilt.
Onions: The bold odor of onions may repel pests in and of itself, or perhaps the pests are confused by its ability to mask the fragrance of their preferred host plants. Either way, onions in the cucumber patch may scare off cucumber beetles, and planting them between carrot rows serves to repel adult carrot root maggot flies. Circling a row of onions around tomato plants is said to help repel sap-sucking aphids.
Tansy: 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.
Borage: 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 honeybees and other pollinators.
Castor bean plant: Though it should be grown with care (all parts are extremely poisonous to humans), the castor bean 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 made from the castor oil plant because it works so well.
Horticulturist and author Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. Her website is www.jessicawalliser.com. Send your gardening or landscaping questions to firstname.lastname@example.org or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.