The practice of using flowers and plants to keep bugs away from other plants is called companion planting. Companion planting can also help plants grow stronger or with better flavor, but the most common use of companion plants is to deter pests. Flowers, herbs or even the garden plants themselves can function as companion plants.
The smell of certain flowers can help keep pests off garden plants. Marigold is one of the most commonly used companion plants. It helps keep beetles off asparagus. It also deters Mexican bean beetles and the beetles that eat melon plants. Marigold keeps nematodes off eggplants and repels tomato worm. Nasturtium repels beetles as well. Tansy deters cabbage worm and cutworm. Dwarf zinnias, by contrast, lure predator bugs, which then eat garden pests. Planting a zinnia near cauliflower will draw lady bugs, which in turn eat most of the pests that attack cauliflower.
Borage is a good companion for tomatoes. Not only does borage attract bees, which help pollinate the tomatoes, it also repels tomato worms. Summer savory helps repel bean beetles. Growing savory near beans not only helps keep away pests, it also provides an interesting seasoning for the beans when it comes time to cook them. Sage repels carrot fly. Basil helps repel mosquitoes, flies and hornworms. Dill repels aphids and mites.
It is also possible for one garden plant to serve as a companion plant for another. Horseradish pairs well with potatoes, as the strong-smelling chemical compounds in horseradish deter potato beetle. Radishes attract leaf miners away from spinach. The leaf miners do eat the leaves of the spinach, but they don't damage the edible root. When planted next to radish, the edible leaves of the spinach suffer less damage. Corn and beans are companion plants with a history that goes back hundreds of years. The beans attract predatory insects which feed on the leafhoppers, leaf beetles and fall armyworms, which would otherwise damage the corn.
How to Use Them
You can use an interplanting method to plant companion plants. When most people think of gardens, they think of neat rows with one variety of plant per row. Interplanting, by contrast, means planting not in homogeneous rows but in a grid pattern with different plants occupying side-by-side cells of the grid. French gardens have been planting flowers interspersed with vegetables for centuries. If you want to keep your garden rows, however, you can plant flowers around the perimeter of your garden. You can also plant rows of companion plants next to each other, or you can plant an occasional companion plant in a row of companions.
- Mother Earth News: An In-Depth Companion Planting Guide
- Organic Gardening: Companion Planting
- Seeds of Change: Companion Planting -- So Happy Together!
- National Gardening Association: Companion Planting
- Cornell Cooperative Extension: Companion Planting
- Limestone County Master Gardeners: Companion Plants
- Cass County Extension: Companion Planting
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