Some vegetables, herbs and flowers are best grown side by side
Have you ever noticed how a vegetable can fail in one location, yet thrive in another? It could be the difference lies in the plant next door.
Plant compatibility is the foundation of a gardening technique known as companion planting—a synergistic partnership that encourages plants to thrive and grow.
Companion planting can benefit your garden in five ways: by providing nutrients, by protecting against disease, by repelling pest insects, by attracting beneficial insects and by attracting bug-eating birds.
Plants that Nourish
Certain plant allies improve the flavor of neighboring vegetables by providing nutrients. For example, comfrey, buckwheat and other plants with roots that grow deep can mine nutrients and bring them up to the surface, making them more available to other plants. Alfalfa, clover and other cover crops also nourish neighboring plants with essential nutrients and trace minerals.
Other plants—such as peas, beans, lupines and clover—have the ability to transport nitrogen from the air into their roots, where bacteria can convert it into a plant-friendly form for neighboring plants. In this case, corn, peas and other nitrogen-hungry plants make great companions as they benefit from the “nitrogen-fixing ability” of these legume-type plants.
Plants that Protect
Certain plants can improve the health of their neighbor through a network of defensive chemicals that help ward off plant pests and disease.
Marigolds are a classic example. Both the French and African varieties contain thiopene in their roots, a substance that is toxic to certain types of soil-dwelling nematodes. As such, they make great companions for tomatoes, beans and other plants that are susceptible to nematode damage.
Plants that use similar defensive chemicals to protect against disease-causing pathogens include garlic, onions and chives—well-known compatibles that prevent black spot on roses and scab on apples. Likewise, brassica roots release chemicals that suppress some soil-borne diseases. Equally important are silica-rich plants such as comfrey and borage, which may help neutralize rust, fungal attacks and other water-borne diseases.
Other ways companion plants protect is by keeping other plants cool. Summertime heat can take a toll on radishes, spinach, lettuce and turnips. Larger plants such as pole beans and tomatoes provide shade, conserving moisture and reducing heat that would cause these vegetables to become woody or bolt.
Plants that Repel Pests
Most pests locate their next meal from their host plant’s odor or color. A diversified garden boasts a complexity of plant odors, colors and textures, composing a natural barrier that makes it harder for these pests to locate their target meal.
Strongly scented plants benefit neighboring plants by masking their scent. Rosemary, sage, lavender, oregano and other strong-smelling plants often foil aphid attacks on susceptible neighbors. Another strategy is to plant the garden perimeter with garlic and marigolds to repel aphids and beetles.
Other plants contain phytotoxins that lure, then sicken or kill dining pests. Mustard oils found in cabbage and similar plants often poison spider mites, mosquitoes and Mexican bean beetles. Therefore, cabbage, broccoli and kale make good companion plants for beans.
Sometimes a plant can repel bugs simply by creating a physical barrier between the critter and the plant it wants to eat. If raccoons are raiding your corn you might surround it with a scratchy barrier of squash vines.
Catnip is another repellent plant when it comes to flea beetles, potato beetles and green peach aphids. But you don’t have to plant catnip in your garden to benefit from its protection. If you grow it outside the garden, cut it and use it as a protecting mulch.
Additional repellent plants with beneficial qualities are leeks, onions, and rosemary against the carrot fly; parsley and tomatoes against the asparagus beetle; geraniums and petunias against leafhoppers; southernwood against cabbage moths; and nasturtiums against whiteflies.
Plants that Attract Beneficial Insects
In this case you want to attract bugs—at least when it comes to attracting beneficial insects that prey on pests. These insects seek out and destroy pests such as aphids, slugs and snails, cucumber beetles, caterpillars and other nasty bugs that wreak havoc in our gardens.
Adult beneficials and their larvae feed on insects. However, these hard-working adults also need pollen- and nectar-rich flowers to survive. Begin with spring-flowering plants such as sweet alyssum and sweet woodruff. Include long-blooming plants such as marigolds, coreopsis and petunias. Then extend the season with later-blooming asters, chrysanthemums and salvias.
Attract parasitic wasps, lacewings and syrphid flies with flowering members of the umbel family, including yarrow, parsley, dill and chamomile. Doing so will greatly reduce pest populations of caterpillars, aphids, leafhoppers and thrips. Sunflowers, echinacea, cosmos, zinnias and other members of the daisy family are prime flowers for luring in large predatory insects that dine on cucumber beetles, grasshopper eggs, slugs and caterpillar pests.
Plants that Attract Bug-Eating Birds
Another way to keep bad bugs in check is to attract birds that also feast on insects. Bugs from soil-dwelling grubs to codling moths in flight provide a first-class feast for chickadees, robins, wrens, swallows and other bug-eating birds.
The best way to attract these beneficial birds is to grow a mix of nectar-, seed- and fruit-bearing plants. For example, cosmos, asters, zinnias, sunflowers and other seed-bearing annual or perennial plants attract a variety of songbirds that also feast on insects.
Tubular- or bell-shaped flowers rich in nectar—such as bee balm, pineapple sage, nicotiana, verbena and salvia—lure in hummingbirds, which also dine on caterpillars and small insects.
Companion planting is all about diversity, which is key to any healthy garden. So go ahead and experiment with your own companion plantings.
Grow flowers and herbs among your vegetables. For that matter, tuck in a variety of vegetables in your flower bed. The result is bound to be a more beautiful, sustainable and bountiful garden.
A Sampling of Beneficial Garden Companions
Grow companion plants as a border around other plants, or mixed within rows or throughout a bed.
Basil: enhances growth, repels flying insects; plant with lettuce, peppers, tomatoes.
Beans: deters potato beetles, fixes nitrogen; plant with cabbage family, corn, eggplant, lettuce, marigolds, petunias, potatoes.
Carrots: keep away from dill; plant with lettuce, marigolds, onions, parsley, tomatoes.
Cabbage family: keep away from strawberries and tomatoes; plant with aromatic herbs, chamomile, marigolds, onions, nasturtiums, potatoes.
Cucumbers: keep away from sunflowers and potatoes; plant with lettuce, nasturtiums, onions, peas, petunias, radishes.
Geraniums: repels cabbage worms, Japanese beetles; plant with cabbage family, grapes.
Lettuce: compatible with most garden plants; plant with beans, cabbage family, calendula, carrots, onions, peas, pansies, radishes.
Marigolds: repels aphids, potato and squash bugs; mass plantings kill nematodes; OK to plant with all garden plants.
Onions: deters many pests, masks plant odors; plant with most garden plants, except peas and beans.
Peas: fixes nitrogen; plant with carrots, corn, cucumbers, potatoes.
Peppers: keep away from fennel; plant with basil, carrots, onions, parsley.
Radishes: repels cucumber bettles; plant with carrots, cucumbers, squash.
Tomatoes: keep away from fennel and potatoes; plant with basil, carrots, chamomile, marigolds.