Companion Planting Chart 2026 ▷ What to Plant Together (and What to Avoid)

▷ Companion planting chart 2026

How companion planting works: the science

Companion planting works through several distinct mechanisms — and not all are equally well-supported by research:

Chemical deterrence (moderate evidence): Some plants release volatile compounds through their leaves or roots that repel specific pests. Basil releases linalool and estragole that reduce thrips on nearby tomatoes (demonstrated in multiple studies). Marigolds produce alpha-terthienyl in their roots, which kills nematodes. The effect radius is typically within 12–18 inches of the companion plant.

Physical interference (strong evidence): This is the most reliably documented mechanism. Tall plants provide shade to heat-sensitive crops (lettuce under tomatoes or sunflowers). Dense groundcover plants (squash leaves, nasturtiums) suppress weeds by blocking light. Prickly or hairy plant surfaces deter crawling pests physically.

Beneficial insect attraction (strong evidence): Flowers with accessible nectar attract parasitic wasps, hoverflies, and lacewings that prey on common garden pests. Sweet alyssum, phacelia, and borage are the most documented in this category.

Nutrient sharing (well-documented): Legumes (beans, peas, clover) fix atmospheric nitrogen through a symbiotic relationship with Rhizobium bacteria. This nitrogen becomes available to neighboring plants. The Three Sisters system leverages this directly — beans feed corn and squash.

Trap cropping (evidence-supported): Some plants attract pests away from crops you want to protect. Nasturtiums draw aphids strongly — plant them at garden margins and aphids colonize the nasturtiums rather than your vegetables. Blue Hubbard squash is planted as a trap crop for squash vine borer and cucumber beetles.

Best companion planting combinations

Tomatoes: best and worst companions

Basil + tomatoes: The most popular companion planting pair, and one with reasonable scientific backing. Basil's aromatic oils (linalool, eugenol) measurably reduce thrips and may deter aphids. Plant basil 12–18 inches from tomatoes, not directly under them. Any basil variety works; compact varieties like 'Spicy Globe' or 'Minette' are ideal for interplanting as they won't compete for space.

Marigolds + tomatoes: French marigolds (Tagetes patula) are the most effective — their root exudates kill soil nematodes. For best effect, plant densely (6–8 inches apart) as a border row. Start marigold seeds indoors 6 weeks before tomato transplanting so they're established when tomatoes go in. 'Nema-gone' and 'Tangerine' are varieties specifically bred for nematode control.

Avoid: fennel + tomatoes: Fennel releases allelopathic compounds that stunt the growth of most garden plants, including tomatoes. Keep fennel completely separate from the vegetable garden — grow it in its own container or a dedicated herb bed.

Carrots: the best companions

Carrots pair exceptionally well with onions, leeks, and chives — this combination is one of the best-documented pest-deterrent pairs in home gardening. Carrot fly (Psila rosae) is repelled by the smell of alliums, while onion fly (Delia antiqua) is deterred by the smell of carrots. The combination provides mutual protection. Plant in alternating rows: one row carrots, one row onions, repeating throughout the bed. Rosemary and sage planted at the border also deter carrot fly through aromatic compounds.

Brassicas (cabbage, kale, broccoli)

Brassicas are particularly vulnerable to the cabbage white butterfly (Pieris rapae) and cabbage moth. The most effective companion planting strategy: aromatic herbs planted closely to confuse the butterfly's smell-based host-finding. Rosemary, thyme, sage, and dill are all effective. Nasturtiums planted at the border serve as a trap crop — cabbage aphids strongly prefer nasturtiums. The plants also benefit from onion and garlic borders, which deter multiple brassica pests.

Cucumbers and courgettes

Cucumbers and courgettes (zucchini) are heavy feeders that benefit from companions that attract pollinators (both require pollination for fruit set) and deter cucumber beetles. Best companions: borage (powerful pollinator attractant — nearly every bee and bumblebee will visit), radishes as trap crop for cucumber beetle, and beans (fix nitrogen for the hungry cucurbits). Plant dill while young only — mature dill can inhibit cucumber growth.

The Three Sisters: the most powerful companion system

The Three Sisters — corn, climbing beans, and winter squash — is the most complete and scientifically validated companion planting system available. Developed by the Haudenosaunee (Iroquois) Confederacy and other Indigenous peoples over thousands of years, it provides nutritional balance, soil improvement, and space efficiency in a single planting unit.

How to plant the Three Sisters (per mound, plant 2–3 mounds at least 4 feet apart):

1. Create a mound 18 inches wide and 6 inches tall in enriched soil. Flatten the top.
2. Plant 4–5 corn seeds in the center, 6 inches apart. Water well.
3. After 2 weeks (corn is 4–5 inches tall), plant 4 bean seeds in a ring around the corn, 6 inches from each plant.
4. One week later, plant 2–3 squash seeds at the base of the mound edges.
5. Thin to the strongest seedlings as they establish. Keep evenly moist through germination.

The system works regardless of corn variety (sweet corn, popcorn, or flour corn), bean type (any climbing bean — Blue Lake, Kentucky Wonder, Scarlet Runner), or squash species (butternut, acorn, Hubbard, or traditional pumpkin). Blue Hubbard squash is particularly recommended as it also acts as a trap crop for squash vine borer and cucumber beetles, protecting the main planting.

Best flowers for the vegetable garden

Adding flowers to a vegetable garden is one of the highest-return companion planting strategies: flowers attract the beneficial insects that pollinate crops and prey on pests. The best choices:

• Phacelia tanacetifolia: Rated the single most effective plant for attracting beneficial insects in UK research studies. Direct sow in early spring; flowers within 6–8 weeks. Plant in gaps between vegetable rows.
• Sweet alyssum (Lobularia maritima): Small white flowers provide nectar for parasitic wasps that prey on caterpillars. Plant as border or living mulch between vegetables.
• Borage: Attracts pollinators, particularly bumblebees critical for tomato and squash pollination. Self-seeds freely. Both leaves (cucumber flavor) and flowers are edible.
• Nasturtiums: Trap crop for aphids; edible flowers and leaves; attract beneficial insects. Let them sprawl at garden edges.
• Calendula (pot marigold): Attracts aphid predators; the sticky stems trap whiteflies. Edible flowers. More cold-tolerant than French marigolds.

Bad companion combinations to avoid

Frequently asked questions

Frequently Asked Questions

What is companion planting and does it actually work?

Companion planting is the practice of growing different plants in close proximity to benefit each other through pest deterrence, pollination support, nutrient exchange, or physical support. The scientific evidence is mixed — some combinations have strong research backing (Three Sisters: corn, beans, squash), while others are primarily folk gardening wisdom with limited controlled studies. What the evidence supports: marigolds and basil near tomatoes do measurably reduce certain pests; aromatic herbs near brassicas deter cabbage moths; tall plants providing shade to heat-sensitive crops is an undeniable physical benefit. The honest answer: companion planting works best as one tool among several, not a replacement for proper soil preparation, pest monitoring, and watering. Even if the pest-deterrence effects are modest, companion planting maximizes space use in small gardens and adds visual diversity — both are real benefits.

What should I not plant next to tomatoes?

Avoid planting near tomatoes: fennel (releases chemicals that inhibit tomato growth — one of the most well-documented bad companion pairs), brassicas like cabbage, kale, and broccoli (compete for the same soil nutrients and attract different pests that then spread), corn (both are heavy feeders that compete for nitrogen, and corn attracts the same pests as tomatoes — corn earworm/tomato fruitworm is the same species), potatoes (both are nightshades that share blights and diseases — if one gets late blight, the other will too). Good tomato companions: basil (reduces thrips and aphids, most studies support this), marigolds (repel nematodes and aphids), borage (attracts pollinators, may deter tomato hornworm), parsley, and carrots.

What is the Three Sisters companion planting method?

The Three Sisters is the most famous and best-documented companion planting system, developed by Indigenous peoples of North America and used for thousands of years. The three plants: corn, beans (pole/climbing), and squash (winter squash or pumpkin). How it works: the tall corn provides a natural trellis for the beans to climb; the beans fix atmospheric nitrogen in the soil via root bacteria, feeding the nitrogen-hungry corn; the large squash leaves act as living mulch — shading the soil to retain moisture, suppress weeds, and deter pests (the prickly squash leaves and vines deter animal pests). The system also provides a nutritionally complete diet (carbohydrate from corn, protein from beans, vitamins from squash). To plant: create a mound 18 inches wide, 6 inches tall. Plant 4 corn seeds in the center first. After 2 weeks when corn is 4–5 inches tall, plant 4 bean seeds around the corn. One week later, plant 2–3 squash seeds at the base of the mound.

Can I plant garlic and onions near all vegetables?

Garlic and onions (alliums) are among the most versatile companion plants — they deter a wide range of pests including aphids, Japanese beetles, carrot rust fly, and codling moth. They pair well with: roses (garlic is a classic rose companion that reduces aphids and black spot), carrots, tomatoes, brassicas, and lettuce. However, avoid planting alliums near: legumes (beans and peas), as onion family plants inhibit the growth of all bean and pea species — this is one of the most consistently documented negative companion plant relationships. Also avoid near asparagus (competition) and sage (both need similar conditions but inhibit each other). One practical tip: garlic planted in fall around perennial roses benefits from the same timing as most rose care.

What flowers should I plant in a vegetable garden?

The best flowers for vegetable gardens serve multiple functions: pest deterrence, pollinator attraction, and edibility. Top choices: marigolds (Tagetes) — the most researched vegetable garden flower; French marigolds (T. patula) release limonene which repels whiteflies, aphids, and nematodes. Plant densely at garden edges and between rows. Nasturtiums — edible flowers, attract beneficial insects, and act as trap crops for aphids (aphids prefer nasturtiums over vegetables — a sacrifice plant strategy). Borage — attracts pollinators, especially bees that also pollinate tomatoes and squash; leaves and flowers are edible. Phacelia — extremely attractive to pollinators, grows quickly from seed, and has no pest issues. Sweet alyssum — provides nectar for parasitic wasps (which prey on caterpillars and aphids) and can be used as living mulch between vegetables. Sunflowers — provide shade for lettuce in summer heat and attract pollinators; also attract aphids (trap crop function).