Companion Planting Chart: The Complete Guide to Plant Pairings

What Is Companion Planting and Why It Works

Companion planting is the practice of growing certain plants near each other for mutual benefit. Some plants repel pests that attack their neighbors, while others attract beneficial insects or improve soil nutrients. This centuries-old technique reduces the need for chemical pesticides and can boost yields by 10 to 20 percent.

The science behind companion planting involves allelopathy (chemical interactions between plants), physical interactions (shade, wind protection), and ecological relationships (attracting predatory insects). Understanding these mechanisms helps you make informed choices rather than relying on gardening myths.

Best Tomato Companion Plants

Tomatoes benefit from several companion plants that deter their most common pests. Basil repels aphids, whiteflies, and tomato hornworms while potentially improving tomato flavor. Marigolds planted around tomato beds release chemicals that repel root-knot nematodes from the soil.

• Basil: Repels aphids, whiteflies, and hornworms — plant within 18 inches of tomatoes
• Marigolds: French marigolds kill root-knot nematodes and deter whiteflies
• Carrots: Loosen soil around tomato roots and maximize garden space
• Borage: Attracts pollinators and repels tomato hornworms
• Garlic: Repels spider mites and aphids — plant as a border

Avoid planting tomatoes near brassicas (cabbage, broccoli, cauliflower), fennel, or mature dill. These plants either compete for nutrients or release chemicals that stunt tomato growth.

Companion Plants for Peppers and Squash

Peppers thrive alongside tomatoes since they share similar growing requirements without competing aggressively. Spinach and lettuce planted beneath pepper plants act as living mulch, keeping soil cool and moist while using space efficiently.

Squash benefits enormously from the Three Sisters planting method: corn provides a trellis for beans, beans fix nitrogen for corn and squash, and squash leaves shade the soil to retain moisture and suppress weeds. This Indigenous American technique remains one of the most effective companion planting strategies known.

• Peppers + basil: Basil repels aphids and thrips that attack pepper plants
• Squash + nasturtiums: Nasturtiums act as trap crops, luring aphids away from squash
• Peppers + carrots: Carrots loosen subsoil without competing for space
• Squash + radishes: Radishes repel squash vine borers when planted around the base

Herb Companions That Repel Pests Naturally

Herbs are the workhorses of companion planting. Their strong aromatic oils confuse pest insects that navigate by scent, creating a natural pest barrier. Strategic herb placement throughout the garden reduces pest pressure across all crops.

• Rosemary: Deters cabbage moths, carrot flies, and bean beetles — plant near brassicas
• Dill: Attracts lacewings, ladybugs, and parasitic wasps — excellent near cabbage and lettuce
• Chives: Repel aphids and Japanese beetles — ideal border plant for roses and tomatoes
• Thyme: Deters cabbage worms when planted among brassicas
• Cilantro: Attracts hoverflies that consume aphids — let some bolt to flower

Flowers as Companion Plants: Beyond Beauty

Flowers serve critical roles in the companion planting system beyond aesthetic appeal. They attract pollinators needed for fruit set, lure beneficial predatory insects, and can act as trap crops that sacrifice themselves to protect your vegetables.

Marigolds deserve special attention — French marigolds (Tagetes patula) release alpha-terthienyl into the soil, a compound toxic to root-knot nematodes. Plant them as a solid border around vegetable beds and leave roots in the soil at season’s end to maximize nematode suppression.

• Sunflowers: Attract aphid-eating ladybugs and provide structural support for climbing beans
• Zinnias: Draw butterflies and hummingbirds for pollination — heat and drought tolerant
• Sweet alyssum: Low-growing ground cover attracts hoverflies and parasitic wasps
• Calendula: Sticky leaves trap whiteflies and aphids — excellent trap crop near tomatoes
• Cosmos: Attract lacewings, parasitic wasps, and other beneficial predators

Plants You Should Never Grow Together

Some plant combinations are actively harmful. Allelopathic plants release chemicals that inhibit neighboring plant growth, while others compete so aggressively for the same resources that both suffer. Avoiding bad pairings is as important as choosing good ones.

• Fennel + almost everything: Fennel inhibits growth of most garden plants — grow it in isolation
• Black walnut + tomatoes, peppers, eggplant: Juglone from walnut roots kills nightshade family plants
• Onions + beans and peas: Onion compounds inhibit nitrogen-fixing bacteria that legumes depend on
• Dill + carrots: Cross-pollinate and produce poor-quality seeds — keep at least 15 feet apart
• Potatoes + tomatoes: Same family, share blight diseases — separate by maximum distance possible
• Cabbage + strawberries: Both attract the same pests, creating concentrated infestations

How to Design a Companion Planted Garden Bed

Designing a companion planted bed starts with your primary crops. List what you want to grow, identify their main pest and disease challenges, then select companions that address those specific problems. Avoid the common mistake of planting too many companion species in too small a space.

A practical 4 by 8 foot raised bed might include tomatoes as the central crop, with basil interplanted between them, marigolds along the border, and carrots filling the spaces between plants. This focused approach is more effective than trying to include every beneficial companion.

Rotate your companion planting combinations annually. Even beneficial plant relationships can lead to soil depletion or pest adaptation if repeated in the same location. Treat companion planting as part of your overall crop rotation strategy.

Companion Planting in Containers and Small Spaces

Container gardeners can benefit from companion planting by grouping compatible plants in large pots or arranging separate containers strategically. A single large container with a tomato plant, two basil plants, and trailing nasturtiums creates an effective companion planting system on a balcony.

Window boxes work well for herb combinations that repel indoor and outdoor pests. A box of basil, chives, and parsley near a kitchen window deters flies while providing fresh herbs. Pair containers of aromatic herbs with vegetable pots on a patio for pest deterrence.

• Large pot combo: Tomato + basil + parsley in a 15-gallon container
• Hanging basket: Strawberries + thyme — thyme repels slugs and improves berry flavor
• Window box: Chives + lettuce + marigolds — continuous harvest with built-in pest protection
• Raised bed corner: Sunflower + pole beans + squash — mini Three Sisters planting