Companion Planting Guide by Zone: What Grows Well Together

April 27, 2026

Companion planting works — but the timing of it is zone-dependent in ways most generic guides ignore. A tomato-basil pairing that thrives in zone 7 may never hit its stride in zone 4, where basil struggles to establish before tomatoes need full support. This guide organizes companion planting by USDA hardiness zone so you can match the right pairings to your actual growing season.

If you want zone-matched planting calendars alongside these pairings, the GardeningByZone books library has regional guides that cover succession timing, spacing, and variety selection for your specific climate.

What Is Companion Planting and Why Does Zone Matter?

Companion planting is the practice of growing two or more plant species in close proximity so that one or both benefit. The mechanisms include pest confusion, pollinator attraction, nitrogen fixation, physical support, and microclimate moderation.

Zone matters for companion planting because benefit windows are time-constrained. Nitrogen-fixing legumes only help neighbors if they’re in the ground long enough to fix meaningful nitrogen before the main crop’s critical growth period. Pest-repelling herbs only protect neighbors during the pest’s active season. A zone 5 gardener and a zone 9 gardener may plant the same pairs, but the zone 5 gardener needs to start earlier indoors and sequence more carefully to capture the benefit window.

The Core Companion Planting Mechanisms

• Pest repulsion. Strong-scented herbs and alliums confuse or deter insects that navigate by smell.
• Trap cropping. Sacrificial plants lure pests away from the main crop.
• Pollinator attraction. Flowering companions draw bees and beneficial insects into the garden.
• Nitrogen fixation. Legumes host rhizobial bacteria that convert atmospheric nitrogen into plant-available forms.
• Physical structure. Tall plants shade heat-sensitive crops; climbing plants use sturdy neighbors as support.
• Allelopathy. Some plants release root or foliar compounds that suppress competing weeds or inhibit nearby plants (fennel is the most common offender).

What to Avoid

Fennel is the companion planting pariah — it inhibits most vegetables and should be grown in isolation or at the garden’s edge. Keep it away from tomatoes, peppers, basil, and kohlrabi.

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Zones 3–5: Short-Season Companion Strategies

Zones 3–5 carry frost into May and can see the first fall frost in September. The growing window is compressed, which means companion pairings need to do double duty — protecting crops while also making the most of a short season. If you’re not sure which zone you’re in, the zones 4a and zones 5b landing pages include frost-date ranges and planting windows for those climates.

The Northeast Vegetable Gardening guide covers succession timing for these pairings in detail, including when to start companions indoors so they’re ready to protect transplants from day one.

The Three Sisters (Corn, Beans, Squash)

The Three Sisters is the most documented companion system in North America and it works exceptionally well in zones 4–5 where the season is long enough for corn to mature. Plant corn first and wait until it’s 6 inches tall before direct-sowing green beans at its base. Add squash-summer or pumpkins around the perimeter after beans emerge.

• Corn: vertical structure for beans to climb
• Beans: nitrogen fixation that feeds corn’s heavy feeding
• Squash: ground cover that suppresses weeds and retains soil moisture

In zone 3, start corn indoors 2–3 weeks before last frost and transplant carefully — corn dislikes root disturbance, so use biodegradable pots.

Brassicas and Alliums

Cabbage, broccoli, cauliflower, and kale are all prime targets for cabbage moths and aphids. Interplanting with onions, garlic, or chives disrupts the scent trails insects use to locate brassicas.

Row pattern: alternate a brassica plant with an allium plant every 12 inches along the row. This is more effective than planting alliums in a separate border.

Carrots and Tomatoes

Carrots loosen soil around tomato roots, and tomatoes shade carrots during the hottest part of the short zone 4–5 summer. Plant carrots first (they take longer to germinate), then transplant tomatoes into the same bed. The carrots will be partially shaded as tomatoes size up, which suits them — carrots grown in partial shade are often sweeter.

Chives planted at the ends of carrot rows add aphid deterrence for both crops.

Flowers for Zones 3–5

• Marigolds: Plant French marigolds throughout the vegetable garden. They deter nematodes and aphids and attract predatory wasps.
• Nasturtiums: Use as a trap crop for aphids. Plant at the garden perimeter and check them weekly — when aphids colonize nasturtiums, remove and compost the affected stems before the colony migrates.
• Calendula: Attracts beneficial insects including hoverflies, whose larvae eat aphids.

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Zones 6–8: The Broadest Companion Planting Window

Zones 6–8 cover a huge swath of the country — from the mid-Atlantic through the Southeast and into the lower Midwest and Pacific Northwest. The longer season means you can run succession companion plantings: cool-season companions in spring, then warm-season companions through summer, then a cool-season second round in fall. The zone 7a and zone 8b pages lay out the frost windows that govern when each succession set goes in.

The Southeast Vegetable Gardening guide covers succession timing for these pairings in detail, including the transition window between spring and summer companion sets that zone 7–8 gardeners can exploit.

Tomatoes, Basil, and Marigolds

This is the classic warm-season trio and it earns its reputation. Basil planted 12–18 inches from tomatoes repels thrips and aphids, and is consistently reported to improve tomato flavor among growers (the evidence is anecdotal but persistent). French marigolds in the same bed deter whiteflies and nematodes.

In zone 6, start basil indoors 6 weeks before last frost. It cannot go outside until nights stay reliably above 50°F — transplanting too early stalls basil and eliminates the benefit window.

Peppers, Basil, and Carrots

Peppers and basil are a natural pair: basil repels aphids and spider mites, both common pepper pests. Add carrots as a soil-loosening underplanting — their roots break up compaction in pepper beds, which benefits drainage.

Avoid planting peppers near fennel or kohlrabi — both can stunt pepper growth.

Cucumbers and Radishes

Cucumbers are beetle magnets. Interplanting with radishes deters cucumber beetles — radishes act as a trap crop. Plant radishes densely around cucumber hills and allow some to bolt and flower, which attracts predatory insects.

Nasturtiums serve double duty here: trap crop for aphids and attractive ground cover that keeps cucumber beetles disoriented.

The Spring-to-Summer Succession Sequence

Zone 7–8 gardeners can run two distinct companion sets.

Spring (cool season): Plant lettuce under tall peas. Peas fix nitrogen, and their climbing structure shades lettuce during warm spells that would otherwise bolt the crop. Add spinach and radishes as quick-maturing fillers.

Summer (warm season): When peas finish, pull them and turn them into the bed (their nitrogen-fixed roots decompose quickly). Transplant tomatoes or eggplant into the now nitrogen-enriched soil, and add basil and marigolds.

This succession sequence is the most efficient use of zone 6–8 bed space and produces two full companion-planting cycles per season.

Flowers for Zones 6–8

• Zinnias: Attract predatory wasps and hummingbirds; excellent near cucumbers and squash-summer.
• Borage: Companion to tomatoes and squash; repels tomato hornworm and attracts pollinators.
• Cosmos: Long bloom season keeps beneficial insects present throughout the zone 6–8 growing window.

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Zones 9–11: Heat-Season Companion Planting

Zones 9–11 flip the companion planting logic. The challenge isn’t a short season — it’s a brutal summer that halts cool-season crops entirely. Companion planting in these zones is primarily about heat mitigation, shade provision, and keeping the garden productive through transitions. See the zone 9b and zone 10a pages for the specific date windows that govern the fall planting window in these climates.

The Southwest Vegetable Gardening guide covers companion timing for these pairings in detail, including the fall planting window that functions as the zone 9–11 “second spring.”

Shade Companions for Summer Heat

In zones 9–11, corn and okra function as living shade structures. Plant heat-tolerant but sun-sensitive crops like sweet potatoes and peas in their partial shade. Okra’s height (6–8 feet) provides afternoon shade on the west side of a bed — orient rows north-to-south and place heat-sensitive crops on the east side.

Tomatoes and Basil in Zones 9–11

Tomatoes in zone 9 need to be in the ground early — by February or March in many areas — to fruit before summer heat shuts them down. Basil planted at the same time provides pest protection during the productive spring window.

When temperatures climb above 95°F consistently, both tomatoes and basil will stall. Cut basil back hard to prevent bolting and it may recover in fall. Some zone 9 gardeners treat basil as a perennial that dies back in summer and re-emerges when temperatures moderate.

Sweet Potatoes as Living Mulch

Sweet potatoes are an underused zone 9–11 companion. Their dense vining growth functions as living mulch, suppressing weeds and retaining soil moisture around taller crops like okra and peppers. They also tolerate intense heat that would wilt most ground covers.

Plant sweet potatoes at the base of taller crops and let them sprawl. Harvest timing works out naturally: sweet potatoes are ready in fall, just as the tall crops are winding down.

The Fall “Second Spring” Succession

Zone 9–11 gardeners have a second companion planting window in fall that mirrors the zone 3–5 spring window. Once temperatures drop below 90°F (typically September in zone 9, October in zone 10):

1. Plant a Three Sisters set for a fall corn harvest.
2. Interplant lettuce and spinach under tomatoes transplanted for a fall crop.
3. Add marigolds and zinnias to maintain pollinator activity through the shorter fall days.

Flowers for Zones 9–11

• Zinnias: Heat-tolerant pollinator magnet; African varieties handle zone 10 summers well and keep beneficial insects present when other flowers fail.
• Marigolds: More heat-tolerant than most companion flowers; African varieties handle zone 10 summers better than French types.
• Nasturtiums: Plant in fall only in zones 10–11; they cannot tolerate zone 10 summer heat.

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Companion Planting Pairs Quick Reference

Main Crop	Good Companions	Avoid
Tomatoes	Basil, marigolds, carrots, borage	Fennel, kohlrabi
Peppers	Basil, carrots, marigolds	Fennel
Cucumbers	Radishes, nasturtiums, dill	Sage
Squash	Corn, beans, nasturtiums, borage	Potatoes
Brassicas	Onions, garlic, chives, dill	Strawberries, tomatoes
Carrots	Chives, tomatoes, rosemary	Dill (mature)
Beans	Corn, squash, carrots, marigolds	Onions, garlic
Lettuce	Tall peas, chives, radishes	Celery

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Internal Timing: When to Plant Companions Relative to Main Crops

The most common companion planting mistake is planting companions at the same time as the main crop, then wondering why they didn’t help. Companions need a head start or need to be synchronized to the pest or benefit window.

Fast-maturing crops as companions (radishes, lettuce, spinach): Direct-sow at or slightly before the main crop. They’ll be producing in 30–45 days.

Herbs as companions (basil, chives, dill, parsley): Start indoors 4–6 weeks before the main crop transplant date. They need to be established — not struggling — when they go in next to the main crop.

Flowers as companions (marigolds, nasturtiums, zinnias): Start indoors 6–8 weeks before last frost. Marigolds need to be in bloom to deter nematodes — seedlings don’t count.

Alliums as companions (garlic, chives, onions): Garlic is planted in fall for spring companion benefit. Chives and onions can go in at soil temperature 40°F, well before most warm-season main crops.

For zone-specific timing, see the seed starting guide and the spring planting checklist.

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What to Plant With Specific Crops: A Closer Look

Tomatoes

The most-asked companion question. Tomatoes benefit from:

• Basil: Aphid and thrip repulsion; plant 12–18 inches away
• Marigolds: Nematode and whitefly deterrence; French variety is most effective
• Borage: Hornworm deterrence; also attracts pollinators
• Carrots: Root aeration; carrots interplanted with tomatoes may be smaller but the bed benefits overall
• Chives: Aphid repulsion; plant at bed corners

Avoid: fennel, kohlrabi, brassicas (they compete for similar nutrients and brassica pests can spread to tomatoes).

Squash and Pumpkins

Squash and pumpkins benefit from:

• Corn: Vertical structure; squash shades corn’s root zone
• Nasturtiums: Aphid trap crop; plant at the vine tips
• Borage: Squash bug deterrence; established borage planted at squash hills reduces squash bug pressure noticeably
• Marigolds: Nematode protection in beds where squash follows tomatoes or peppers

Avoid: potatoes — they share fungal disease vectors.

Beans

Green beans and lima beans are compatible with most crops but have specific synergies:

• Corn: Classic Three Sisters pairing; beans fix nitrogen for corn
• Squash: Ground cover and moisture retention
• Carrots: Soil structure; root patterns complement each other
• Marigolds: Mexican bean beetle deterrence

Avoid: onions and garlic — alliums stunt bean growth, one of the most consistent findings in companion planting trials.

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Building a Companion Planting Plan for Your Zone

A practical companion plan has three components:

1. Anchor crop. Your highest-value or most space-intensive plant. Usually a tomato, pepper, squash, or corn.
2. Pest management companion. Chosen specifically for the pests common in your zone and season. In zones 3–5, focus on aphids and cabbage moths. In zones 6–8, add cucumber beetles and whiteflies. In zones 9–11, add spider mites and squash vine borers.
3. Pollinator companion. A flowering plant timed to bloom during the anchor crop’s flowering period. If the anchor crop flowers in June in your zone, the companion needs to be in bloom by late May.

Map this onto your zone’s frost dates, and you have a companion planting plan that actually works with your growing window rather than against it.

For deeper guidance on herbs as companions — including which herb varieties perform best in each climate — see the complete herb garden planting guide by zone.

And for companion flowers specifically, the best companion flowers for vegetable gardens post covers variety selection, spacing, and bloom-time coordination in detail.

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