Insects can turn a cabbage to lace, bore holes through tomatoes and suck the life out of leafy greens in no time at all. When you grow your own vegetables, you want to control the amount of pesticides you are exposed to and there are steps you can take when planning your garden to minimize pest damage without dousing your veggies in potentially harmful chemicals. Companion planting, in particular the use of herbs, can discourage certain pests from making a meal of your crops. The herbs work either by luring pests away from crops or by repelling them with odors or tastes the pests dislike. The benefit isn't all for the plants, however. Companion gardening yields plenty of fresh herbs for the adventurous cook.
While most vegetable gardens are annual affairs, tilled and replanted each year, it is worthwhile to find some space that can remain undisturbed from year to year to give crops the benefit of pest-repelling perennial herbs. Rosemary, a shrubby perennial in warm climates, repels cabbage moths, bean beetles and carrot flies when planted with those crops. Chives deter aphids, mites and Japanese beetles, as well as rabbits -- a larger garden pest. Sage repels the same insects as rosemary, as well as flea beetles, which prey on potatoes and sweet potatoes. Garlic, a perennial herb, deters Japanese beetles. All varieties of mint are effective against cabbage moths, flea beetles, aphids and even mice, though mints need to be grown in pots because of their invasive habit. Consider edging your entire vegetable garden with a planting of attractive wormwood (Artemesia). Its white foliage discourages slugs as well as small foraging animals.
Annual and Biennial Herbs
Annual herbs and biennial herbs, which are often treated as annuals, are easier to incorporate into a vegetable garden. Basil, a favorite in the kitchen, repels thrips, flies and mosquitoes. Chervil deters slugs, while cilantro repels aphids, potato beetles and spider mites. Dill can keep aphids, spider mites and squash bugs away from vegetables, but should not be planted near tomatoes, because it can attract tomato hornworms. Though not technically herbs, consider brightening your vegetable garden with the annual edible flowers nasturtium and marigold. They are traditionally planted in vegetable gardens with good reason -- nasturtiums deter pests of the cucumber and squash families, like squash bugs, pumpkin and cucumber beetles; marigolds not only repel bean beetles, but their roots produce a chemical that kills a harmful soil-borne pest of many vegetables, root-knot nematodes.
Attracting Good Bugs
Not all insects are bad. There are some bugs that are beneficial to your garden, and some herbs attract them. Bees, for instance, are critical for pollinating vegetable flowers to create the fruit. Ladybugs, green lacewings, ground beetles and hoverflies feed on aphids, mites, scales, mealybugs and other damaging pests. Some parasitic wasps prey on caterpillers and tomato hornworms that damage your veggies. All are attracted to herbs with plenty of nectar, like borage, dill, yarrow, lovage, members of the mint family and fennel. Plant fennel near the edge of the garden because it puts out a chemical through its roots that can diminish the growth of other plants.
It takes more than popping a beneficial plant here and there among your rows or blocks of veggies to make a companion garden that will successfully repel insects. Though long, wide rows of beans, tomatoes or greens are convenient for seeding, watering and weeding, large masses of a single plant are also easy for pests to find. Instead of growing all of one type of vegetable together, interplant vegetables that grow well together and add herbs around them that repel common pests. For instance, tomatoes and lettuce make good use of space, and adding basil not only repels thrips but improves the flavor of tomatoes. In the University of California-Davis Good Life Garden, a demonstration garden on the university's campus, small plantings of squash are surrounded on all sides by a "fort" of interplanted garlic chives and thyme. The thyme repels whiteflies, while the chives have a smell that aphids avoid.
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