What Is Companion Planting?

It takes sunlight, water, and good soil to make plants happy and healthy. But many of them also like the company of other plants to help them thrive. There are specific plants that, when grown in close proximity, offer their neighbors outsized benefits. That's called companion planting.

"Many believe that certain plant combinations have extraordinary (even mysterious) powers to help each other grow," write the editors of Good Housekeeping.

But there's really no mystery to it at all. Companion planting dates back thousands of years and is still used by backyard gardeners and farmers today. The indigenous people living in the Americas practiced many forms of companion planting long before the Europeans arrived.

One of the earliest documented examples was the "Three Sisters" agricultural technique where winter squash, beans, and maize were planted together. The corn provided a stalk for the bean to climb, allowing it to grow high toward the sun. The squash then grew low to the ground, shaded by the corn and beans, while protecting those plants from weeds.

Benefits of companion planting

The Tree Sisters shows just some of the ways plants can support each other.

"The benefits of companion planting include pest control, nitrogen fixation, providing support of one plant by another, enhancing nutrient uptake, and water conservation among other benefits," writes Leonard Githinji, Ph.D., assistant professor and extension specialist at Virginia State University. "Hence companion planting can lead to increased yield, less reliance on pesticide, and increased biodiversity, helping to bring a balanced eco-system to your garden and allowing nature to do its job."

The Old Farmer's Almanac lists many reasons to grow certain plants near each other:

• Shade — Larger plants protect smaller plants from the sun.
• Support — Tall plants like corn and sunflowers can support sprawling crops like cucumbers and peas.
• Better health — A plant can absorb substances from the soil, changing soil biochemistry to help other plants.
• Soil benefits — Some plants make more nitrogen available. Other plants bring up nutrients from deep in the soil, which helps plants with shallow roots.
• Weed control — Sprawling plants cover open areas, stopping weeds from growing.

Here's a look at some common garden plants and their suggested companions.

Tomato companion plants

If you want to offer your tomato plants some helpful companions, dill and basil can protect the tomatoes from hornworms. Todd Weinmann of North Dakota State University Agricultural Extension offers these suggestions for "companions" and "allies" to Burpee. (Companions are plants that are mutually beneficial when grown together, whereas, allies refer to plants that offer protection or help the growth of other plants, explains Cass County Extension.)

Companions include asparagus, carrot, celery, cucumber, onion, parsley and pepper. Plants that offer even more benefits to tomatoes, Weinmann says, include:

Basil — Repels flies and mosquitoes and improves growth and flavor

Bee balm, chives and mint — Improve health and flavor

Borage — Deters tomato worm and improves growth and flavor

Dill — Until mature, improves growth and health (Once mature, it stunts tomato growth.)

Marigold — Deters nematodes (and potted marigolds deter tomato worm and general garden pests.)

Squash companion plants

Corn, melon and pumpkin all make good companion plants for squash, says Weinmann. To take things a step further, there are other plants that play more protective roles.

Marigolds repel beetles. Nasturtiums deter beetles and squash bugs. Oregano protects from pests in general. Borage repels worms, while also helping to improve flavor and growth.

Companion planting peas

When planting peas, consider beans, carrots, corn, cucumbers, radishes and turnips as good neighbors. For an even more beneficial boost, chives are a good option to ward off aphids, and planting mint nearby can help improve health and flavor.

Adding tall plants like corn or sunflowers can give peas a natural trellis to climb so they can make their way up toward the sunshine they crave.

Companion planting herbs

Gardeners know that herbs are beneficial on their own, but they also offer benefits when paired with specific plants. Here are some complementary combinations, according to The Old Farmer's Almanac.

Basil — Plant with tomatoes to repel flies and mosquitoes

Chives — Plant with carrots

Mint — Deters white cabbage moth near cabbage and tomatoes

Oregano — Good with all vegetables

Parsley — Plant near asparagus, corn and tomatoes.

Rosemary — Deters bean beetles, carrot flies and cabbage moths. Plant near cabbage, beans, carrots and sage.

Marigold companion plants

Fiery little marigolds not only add a burst of color to your yard, they do "triple duty in the garden," says Vegetable Gardener.

Specifically French marigolds (Tagetes patula) are an easy and helpful choice for your garden. "Marigolds can call in the beneficial insects, repel unwanted bugs with their strong scent (also masking delicious stuff) and have a compound they emit that battles nematodes in the soil," according to the website.

Other 'companion' planting ideas

You may hear "companion planting" thrown around when talking about flower gardening, too. In this case, however, these are often plants that like similar conditions — lighting, soil, water — but don't necessarily provide one another with any benefits. Sometimes these plants just look good planted next to each other.

Hosta companion plants might include bellflower and geraniums, for example, while hydrangea companion plants might be ferns and foxgloves.

These plant pairings are chosen mostly for looks or for their similar preferences. But for real benefits, gardeners rely on true companion plants, because those not-so "mysterious" beneficial powers can help their neighbors grow big and strong.