What is Companion Planting?
Companion planting is the practice of growing certain crops near each other and keeping others separated so that they all thrive. Companion planting is based mostly on observations passed down from gardener to gardener through the generations, but science can also explain many of the effects, both positive and negative, of growing certain plants together.
The tradition of the three sisters
One of the most well-known examples of companion planting is that of the “Three Sisters” method, used widely by Native American farming societies. Corn, pole beans, and squash are together for mutual benefit to all three. Pole beans use the corn stalks as a means of support while stabilizing the corn and helping restore nitrogen to the soil for future crops. Squash keeps weeds down, shades the soil, and helps prevent moisture from evaporating from the surface.
What are some of the benefits of companion planting?
- Assists in planning the garden layout for maximum benefit to all crops grown.
- Helps repel pests or lure them away from prized plants.
- Attracts pollinators to the garden.
- Provides habitats and food for beneficial insects that control pests.
- Improves conditions (soil, light, support) for neighboring plants.
Even armed with the “why” of companion planting, it can be difficult to know where to start. Here are some guidelines you can use in your own home garden!
In this post, you will find tips on planning your garden with companion plants, then more specific plants for attracting pollinators and repelling pests. Finally, you will find lists of companion plants by vegetable family and further resources. Happy planting!
Planning the Vegetable Garden
Knowing the soil, light, and watering conditions each plant prefers is the most basic way to practice effective companion planting. It is also useful to know the eventual size of your plants, the number of days until harvest, and which diseases affect certain crops. Plant combinations can help improve conditions for neighboring or future plants or, in some cases, impede their growth!
Grow plants that prefer similar conditions together
Peppers and basil, for example, have similar care requirements and grow well when planted together. However, the Nightshade family and the Mustard family prefer different soil acidities and do best when planted separately.
Plant fast growers with slow growers to maximize space
Radishes and baby lettuces mature quickly and will be ready to harvest when crops like squash or melons are just starting to grow large enough to take over their spaces. Radishes are also excellent at marking rows of seeds since they germinate more quickly than most other vegetables. Try sowing radishes to mark rows of carrots, beets, and spinach.
Keep plants prone to similar diseases apart
Tomatoes and potatoes are affected by the same blight, which can spread quickly among them, so avoid planting together. Peppers and beans should not be planted near each other as they are both susceptible to anthracnose.
Grow taller plants to provide shade for leafy greens
It’s always a good idea to leave some asparagus to continue to grow in the garden throughout the summer, in order to provide the plant the energy it needs for next year’s crop (a good rule of thumb is to stop harvesting when the diameter of the spears decreases to the size of a pencil). Each asparagus left in the garden can grow quite tall (up to 6′!) and will “leaf out” into what are called “ferns,” which provide excellent summer shade for plants such as lettuce, Swiss chard, arugula, and spinach.
Separate plants that impede each other’s growth
You might have heard not to plant beans next to onions. But why? Beans are sensitive to the chemical compounds secreted by members of the Lily family: onions, chives, garlic, and shallots. These secretions are called “root exudates” and sensitivity is not limited to planting the two groups together at the same time. Even planting beans in the same area where onions have previously grown can hinder their growth.
The root exudates of broccoli, which stays in the soil where it has recently grown, may hinder the germination of lettuce seeds.
Plant to improve the soil for future crops
Amaranth (also called pigweed) is known as a “dynamic accumulator,” meaning it pulls nutrients from deep within the soil through its long taproot up to its leaves. When the leaves drop and decay (or are composted), the nutrients become available to future plants. Amaranth’s taproot also helps to loosen the soil, providing better growing conditions for root vegetables that are planted in the spot later.
Beans and peas are “nitrogen fixers,” meaning they leave nitrogen in the soil where they were grown or composted. After growing beans, plant nitrogen-lovers, including most leafy greens, leeks, garlic, and scallions.
Attracting Pollinators and Other Beneficial Insects
Many plants attract pollinators and other beneficial insects to the garden, helping to improve harvests and naturally quelling pest populations. Here are a few of our favorites.
Alyssum attracts pollinators and can keep weeds down between rows or plants.
Borage is a great companion plant. It attracts bees and can aid in the pollination of squash, melons, and cucumbers.
Calendula attracts pollinators all through the season.
Chamomile attracts hoverflies and parasitic wasps that prey on garden pests.
Cosmos provides food and habitat for many beneficial insects including bees, parasitic wasps, ladybird beetles, and lacewings.
Dill is a great companion to cabbage, attracting beneficial wasps that feed on cabbage plants.
Gaillardia is a long-blooming perennial that provides rich nectar to pollinators.
Herb flowers attract pollinators in droves and many herbs help repel pests (see below).
Parsley attracts praying mantises, ladybugs, and spiders that dine on garden pests.
Sunflowers attract pollinators and improve the pollination of other crops, particularly squash and pumpkins.
Yarrow is a bee magnet!
Companion Planting to Repel Garden Pests
Certain vegetables and flowers have strong odors or secrete chemicals that can help repel garden pests. Others attract pests and lure them away from other, more prized plants. Below you will find helpful companion plants for pest control.
Agastache, planted a little bit away from the vegetable garden, can lure cabbage moths away from Brassica crops.
Asparagus plants repel nematodes that can attack tomatoes, while tomatoes help repel asparagus beetles. A great, mutually-beneficial pairing!
Basil excels at repelling troublesome insects like aphids, asparagus beetles, flies, and tomato horn worms.
Borage deters tomato hornworms and cabbage moth caterpillars. Best of all, borage is deer-resistant!
Calendula attracts slugs. Plant a bit separate from plants like lettuce to try to lure slugs away.
Carrots have a distinct and strong odor that can help repel pests such as onion fly and leek moth.
Chervil helps repel slugs and attract parasitic wasps that feed on pests. It prefers part shade, so plant with lettuce and spinach under taller crops.
Garlic can help repel rose pests such as aphids.
Hyssop, thyme, celery, and mint can all help repel the cabbage butterfly. Be sure to plant mint in a container, as it can be invasive in the garden.
The odor of leeks can help deter carrot flies.
Marigolds control nematodes in the soil that prey upon tomatoes, cucumbers, and melons.
Nasturtiums repel squash bugs and attract aphids away from other, more prized plants.
When planted with carrot seeds, parsley seeds will help repel carrot flies by masking the carrots’ odor.
Petunias can help repel aphids, asparagus beetles, and leafhoppers.
Sow 2-3 radish seeds in cucumber hills to protect the plants from cucumber beetles. You can let the radishes continue to grow throughout the season and even flower, which will attract pollinators.
Plant radishes next to spinach. They will draw leafminers to their leaves, which won’t affect the radish roots.
Tomatoes repel the diamondback moth larvae that attacks cabbage.
The scent of yarrow repels aphids and attracts hoverflies, ladybugs, and wasps – all of whom eat garden grubs and pests.
Companions by Vegetable Family
Beet Family (Chenopodiaceae)
Examples: spinach, Swiss chard, beets
- Asparagus (for shade)
- Radishes (mark rows, lure away leafminers)
Carrot Family (Apiaceae)
Examples: carrots, celery, parsley, parsnips
- Parley (masks carrot’s odor to throw off pests)
- Leeks (deter carrot flies)
Grass Family (Poaceae)
Examples: corn, wheat, rice, barley
- Squash (shades soil)
- Beans (stabilize corn in wind)
Legume Family (Fabaceae)
Examples: beans, peas
- Corn (acts as a trellis)
- Chervil (repels slugs)
Lily Family (Liliaceae)
Examples: asparagus, onions, leeks, chives, garlic, shallots
- Tomatoes, Basil, Petunias (repel asparagus beetles)
Mustard Family (Brassicaceae)
Examples: broccoli, cauliflower, kale, cabbage, radishes, brussels sprouts
- Tomatoes, Borage (repel cabbage moth larvae)
- Hyssop, thyme, celery, and mint (repel the cabbage butterfly)
- Agastache (lures cabbage moths away)
Nightshade Family (Solanaceae)
Examples: tomatoes, potatoes, peppers, eggplant
- Asparagus, Marigolds (repel nematodes)
- Basil, Borage (deter tomato hornworms)
Squash Family (Cucurbitaceae)
Examples: cucumber, melons, squash
- Radishes (repel cucumber beetles)
- Marigolds (control nematodes)
Sunflower Family (Asteraceae)
Examples: lettuce, radicchio, artichoke
- Calendula (lures slugs away)
- Chervil (repels slugs)
Resources:
Snohomish Conservation District Lawns to Lettuce Program
http://snohomishcd.org/Mother Earth News
https://www.motherearthnews.com/Ed Hume Seeds
https://www.humeseeds.com/