Why Tomatoes Need Companion Plants
Tomatoes are the most popular garden vegetable in America, grown by 86% of gardeners. But growing healthy, productive tomatoes can be challenging with pests like hornworms, aphids, and diseases like blight constantly threatening your harvest.
That's where companion planting comes in. The right companion plants can:
- Repel harmful insects naturally
- Attract beneficial predators
- Improve soil health
- Enhance tomato flavor
- Maximize garden space
- Reduce disease pressure
Scientific studies have shown that tomatoes grown with companions like basil produce up to 20% more fruit and have significantly fewer pest problems than tomatoes grown alone.
Top 10 Best Tomato Companion Plants
These companions have proven benefits for tomatoes:
- 1. Basil - The ultimate tomato companion. Repels aphids, whiteflies, and tomato hornworms. Studies show it can increase tomato yield by 20%. Plant 10-12 inches from tomatoes.
- 2. Marigolds - French marigolds release limonene which deters whiteflies. Their roots release alpha-terthienyl which kills root-knot nematodes. Plant throughout the tomato bed.
- 3. Carrots - Break up soil for tomato roots without competing for nutrients. Tomatoes provide shade for cool-loving carrots. Perfect space-saving combination.
- 4. Nasturtiums - Act as trap crops for aphids. Their trailing habit makes excellent ground cover. Edible flowers are a bonus. Plant at bed edges.
- 5. Garlic - Releases sulfur compounds that deter spider mites and aphids. Plant in fall for next summer's tomatoes or use as border plants.
- 6. Chives - Deter aphids and Japanese beetles. Their purple flowers attract pollinators. Perennial, so plant at bed edges for yearly protection.
- 7. Parsley - Attracts hoverflies whose larvae eat aphids. Also attracts parasitic wasps that control tomato hornworms. Grows well in tomato shade.
- 8. Borage - Improves tomato disease resistance and flavor. Attracts bees for better pollination. Self-seeds readily. One plant per 4 tomatoes.
- 9. Calendula - Sticky stems trap aphids and whiteflies. Attracts beneficial insects. Continuous blooms all season. Plant every 2-3 feet.
- 10. Lettuce - Grows quickly in shade of tomatoes. Maximizes space usage. Living mulch reduces water needs. Succession plant every 2 weeks.
Tomato Companion Benefits Chart
Quick reference guide for tomato companion benefits:
| Companion Plant | Primary Benefit | Secondary Benefits | Planting Distance |
|---|---|---|---|
| Basil | Pest deterrent | Flavor enhancement, attracts pollinators | 10-12 inches |
| Marigolds | Nematode control | Whitefly deterrent, adds color | 12-18 inches |
| Carrots | Soil improvement | Space maximization, weed suppression | 4-6 inches |
| Nasturtiums | Aphid trap crop | Ground cover, edible flowers | 18-24 inches |
| Garlic | Spider mite deterrent | Fungal disease prevention | 6-8 inches |
| Borage | Disease resistance | Pollinator attraction, trace minerals | 24 inches |
| Parsley | Beneficial insect host | Culinary herb, shade tolerant | 8-10 inches |
| Peppers | Similar care needs | Space efficiency, pest confusion | 18-24 inches |
Never Plant These With Tomatoes
These plants will harm your tomato growth and yield:
- **Brassicas (Cabbage, Broccoli, Cauliflower)**: Compete heavily for nutrients. Brassicas stunt tomato growth and tomatoes reduce brassica yields.
- **Fennel**: Releases chemicals that inhibit tomato growth. Fennel is allelopathic to most garden plants - grow it alone.
- **Black Walnut**: Trees release juglone, toxic to tomatoes. Keep tomatoes at least 50 feet from black walnut trees.
- **Corn**: Both attract similar pests (corn earworm = tomato fruitworm). Creates too much shade and competes for nutrients.
- **Dill**: Mature dill stunts tomato growth. Young dill is fine, but it becomes harmful once it flowers.
- **Kohlrabi**: Another brassica that severely stunts tomato growth. They compete for the same nutrients.
Companion Plants for Specific Tomato Pests
For Tomato Hornworms:
Plant dill, parsley, and fennel nearby (not in the same bed) to attract parasitic wasps. These wasps lay eggs on hornworms, naturally controlling them. Borage also repels hornworms effectively.
For Aphids:
Catnip releases nepetalactone which repels aphids strongly. Nasturtiums work as trap crops - aphids prefer them to tomatoes. Garlic and chives create an aromatic barrier aphids avoid.
For Whiteflies:
French marigolds are most effective, releasing limonene. Nasturtiums' sticky leaves trap whiteflies. Basil's essential oils repel them.
For Spider Mites:
Garlic and onions release sulfur compounds toxic to mites. Coriander attracts predatory insects that eat mites. Keep soil moist with living mulch like lettuce.
For Root-Knot Nematodes:
French marigolds are proven nematode killers. Plant them 2-3 months before tomatoes for best effect. Mustard greens as cover crop also reduces nematodes.
Herbs That Love Tomatoes
Herbs make excellent tomato companions because they:
- Require similar growing conditions
- Don't compete heavily for nutrients
- Provide pest control through aromatic oils
- Attract beneficial insects
- Offer culinary combinations
Best Herb Companions:
Basil: Plant sweet basil, Genovese, or Thai basil 10-12 inches from tomatoes. Interplant for maximum pest protection. Some gardeners swear basil makes tomatoes sweeter.
Oregano: Dense ground cover that suppresses weeds. Its flowers attract beneficial wasps. Plant at bed edges as it spreads vigorously.
Thyme: Low-growing, drought-tolerant once established. Attracts hoverflies for aphid control. Use as border plant or between tomato rows.
Sage: Repels flea beetles and carrot flies. Keep 2 feet from tomatoes as mature sage can inhibit growth. Best at garden edges.
Rosemary: Deters cabbage moths that sometimes attack tomatoes. Needs excellent drainage - grow in containers near tomatoes rather than same bed.
Flowers That Protect Tomatoes
Strategic flower planting creates a protective barrier around tomatoes:
- Marigolds: Plant French marigolds (Tagetes patula) every 18 inches throughout bed. Start from seed 6 weeks before tomatoes.
- Nasturtiums: Use as living mulch between plants or trailing from containers. Both leaves and flowers are edible.
- Alyssum: Creates beneficial insect highway at soil level. Self-seeds readily. White varieties most attractive to beneficials.
- Zinnias: Tall varieties provide wind protection. Attract ladybugs and parasitic wasps. Plant on north side to avoid shading.
- Cosmos: Easy from seed, attracts lacewings and ladybugs. Tall varieties good for bed edges, short ones for interplanting.
- Sunflowers: Plant dwarf varieties to attract aphid-eating birds. Tall varieties on north edge for wind protection.
Vegetables That Grow Well With Tomatoes
Peppers: Natural companions sharing the nightshade family. Similar water, nutrient, and temperature needs. Space 18-24 inches apart. Rotate together to new bed yearly.
Carrots: Deep roots break up soil without competing. Tomato canopy provides afternoon shade. Sow carrot seeds when transplanting tomatoes.
Lettuce & Spinach: Use shade under tomatoes for summer growing. Succession plant every 2 weeks. Living mulch reduces soil temperature.
Radishes: Fast-growing markers for slow-germinating carrots. Their penetrating roots improve soil structure. Harvest before tomatoes fully leaf out.
Asparagus: Permanent bed companions. Tomatoes repel asparagus beetles. Asparagus harvested before tomatoes need space. Plant tomatoes 2 feet from asparagus row.
Beans: Bush beans fix nitrogen for heavy-feeding tomatoes. Don't let climbing beans use tomatoes as support. Plant after tomatoes established.
Space-Saving Companion Planting Layouts
Maximize your garden space with these proven layouts:
- **Square Foot Method**: 1 tomato center, 4 basil corners, carrots between (per 2x2 section)
- **Row Garden**: Tomatoes 24" apart, basil between, marigolds at row ends, lettuce as understory
- **Raised Bed (4x8)**: 6 tomatoes, 12 basil, 24 carrots, 8 marigolds at corners and sides
- **Container Combo**: Large pot with 1 tomato, 2 basil, trailing nasturtiums over edge
- **Vertical Garden**: Tomatoes trained up, lettuce below, herbs in pockets, marigolds at base
Timing Your Companion Plantings
6 Weeks Before Last Frost:
Start marigold and basil seeds indoors with tomatoes
2 Weeks Before Transplant:
Direct sow radishes and lettuce where tomatoes will go
Transplant Day:
Plant tomatoes, basil, and marigolds together
Sow carrot seeds around tomatoes
Plant nasturtium seeds at bed edges
2 Weeks After Transplant:
Add second succession of lettuce
Plant bush beans if using
Monthly Through Season:
Succession plant lettuce and radishes
Add more basil from nursery starts
Deadhead flowers for continuous blooms
Fall Planning:
Plant garlic cloves in October for next year's protection
Leave marigold roots to decompose for nematode control
The Science Behind Tomato Companions
Research confirms what gardeners have known for generations:
Basil Study (University of Wisconsin): Intercropping basil with tomatoes reduced thrips damage by 23% and increased marketable yield by 18%.
Marigold Research (North Carolina State): French marigolds reduced root-knot nematode populations by 90% when grown as cover crop before tomatoes.
Trap Cropping (University of Connecticut): Nasturtiums planted as border reduced aphid damage on tomatoes by 65% by serving as preferred host.
Allelopathy (Purdue University): Certain plants release chemicals that help or harm neighbors. Tomatoes release solanine which deters many pests but can inhibit brassica growth.
Beneficial Insects (Cornell): Gardens with diverse companion plantings had 3x more beneficial insects and 60% less pest damage than monoculture plots.