Companion Planting Guide: Which Plants Grow Better Together
Companion planting is the practice of growing certain plants near each other to improve growth, deter pests, attract pollinators, or enhance flavor. While some companion planting advice is rooted in tradition rather than science, many combinations have genuine research support. The Three Sisters (corn, beans, and squash), for example, is a 5,000-year-old system with well-documented benefits. This guide covers the combinations that actually work, explains why, and helps you plan a garden that takes advantage of beneficial plant relationships.
How Companion Planting Works
Companion planting works through several mechanisms. Nitrogen fixation occurs when legumes (beans, peas, clover) host bacteria that convert atmospheric nitrogen into plant-available form, benefiting neighboring plants. Pest deterrence happens when aromatic plants like basil, marigolds, and garlic produce compounds that repel or confuse pest insects. Trap cropping uses sacrificial plants that attract pests away from your main crop.
Physical support is another mechanism: corn provides a living trellis for pole beans. Shade regulation works when taller plants shade heat-sensitive crops in summer. Pollinator attraction from flowering companions increases fruit set on tomatoes, peppers, squash, and other crops that need insect pollination. Not all these effects are dramatic, but combined they contribute to a healthier, more productive garden.
- Nitrogen fixation: legumes feed nitrogen to nearby plants
- Pest deterrence: aromatic plants repel or confuse pests
- Trap cropping: sacrificial plants lure pests away from crops
- Physical support: tall plants provide structure for climbers
- Pollinator attraction: flowers increase fruit set on crops
- Shade regulation: tall plants protect heat-sensitive crops
Proven Companion Combinations
Tomatoes and basil is the most popular combination. Basil repels aphids and whiteflies while potentially improving tomato flavor. Interplant basil at the base of tomato plants. Carrots and onions work together because onion scent deters carrot fly, while carrot scent deters onion fly. Alternate rows of each for mutual pest protection.
The Three Sisters (corn, pole beans, and winter squash) is the most proven companion system. Corn provides structure for beans to climb. Beans fix nitrogen that feeds the corn. Squash leaves shade the ground, suppressing weeds and retaining moisture. Plant corn first, add beans when corn is 6 inches tall, and plant squash between corn hills.
- Tomatoes + basil: pest deterrence, possible flavor enhancement
- Carrots + onions: mutual pest fly deterrence
- Three Sisters: corn + beans + squash = support + nitrogen + weed suppression
- Lettuce under tomatoes: shade from summer heat extends harvest
- Marigolds + anything: repel nematodes, attract beneficial insects
- Cucumbers + nasturtiums: nasturtiums trap aphids away from cucumbers
Plants to Keep Apart
Some plants negatively affect each other through allelopathy (chemical inhibition), competition, or shared pest attraction. Fennel produces compounds that inhibit the growth of most vegetables and should be planted separately. Black walnut trees release juglone, which is toxic to tomatoes, peppers, eggplant, and many other plants within the root zone.
Dill and carrots attract the same pests and should be separated. Potatoes and tomatoes share blight susceptibility and should not be planted near each other. Beans and onions or garlic are poor companions because alliums can inhibit bean growth. Brassicas (broccoli, cabbage) compete heavily with strawberries for nutrients.
Designing a Companion Planting Layout
Plan your garden on paper first, grouping compatible plants together. Create zones: a tomato zone with basil, peppers, and marigolds; a root crop zone with carrots, onions, and radishes; a legume zone with beans, peas, and corn. Leave walking paths between zones for access.
Interplant herbs and flowers throughout the garden rather than relegating them to a separate herb garden. Dill, cilantro, parsley, and fennel attract beneficial predatory insects (lacewings, ladybugs, parasitic wasps) that eat garden pests. A garden with diverse plantings has fewer pest problems than a monoculture of vegetables, even without any pesticide use.
Herbs as Companion Plants
Herbs are the most versatile companion plants because they are compact, aromatic, and many attract beneficial insects. Basil near tomatoes and peppers. Dill near lettuce and cucumbers (but away from carrots). Rosemary and sage near brassicas to deter cabbage moth. Chives near roses and fruit trees to deter aphids.
Let some herbs bolt and flower rather than harvesting all leaves. Flowering dill, cilantro, and parsley are magnets for hoverflies and parasitic wasps, which are among the most effective biological pest control agents in a garden. The flowers are small but produce abundant nectar that sustains these beneficial insects throughout the season.
Frequently Asked Questions
Does companion planting really work?
Some combinations have strong research support: Three Sisters, marigolds for nematode suppression, and aromatic herbs for pest deterrence are well documented. Other traditional pairings have less scientific backing but centuries of grower observation. The overall principle of plant diversity reducing pest problems is firmly established.
What should I not plant near tomatoes?
Avoid planting brassicas (broccoli, cabbage, cauliflower) near tomatoes, as they compete for nutrients. Keep potatoes away because they share blight diseases. Fennel inhibits tomato growth. Corn near tomatoes can create pest management challenges as both attract the corn earworm/tomato fruitworm.
Can I companion plant in raised beds?
Absolutely. Raised beds are ideal for companion planting because the intensive spacing puts plants close enough for companion effects to work. In a 4x8 bed, you might plant tomatoes in the center with basil interplanted, marigolds at the edges, and lettuce underneath for shade.
Do marigolds really repel pests?
French marigolds suppress root-knot nematodes in the soil, which is well documented. They also attract hoverflies and other beneficial insects. Their effect on above-ground pests like aphids is less dramatic but they contribute to overall garden health. They are one of the most cost-effective companion flowers you can plant.