Companion Planting Chart
Some companion planting claims are well supported — mostly the ones about pest confusion, shade and space. Others are folklore. This chart separates them.
What actually works, and why
- Smell masking — strong-scented herbs can confuse pests looking for their host plant. This is the best-supported mechanism.
- Trap cropping — sacrifice a plant pests prefer, and they leave your main crop alone.
- Physical structure — tall plants shading lettuce, or a trellis giving beans somewhere to climb.
- Ground cover — low plants suppressing weeds and holding moisture.
- Nitrogen — legumes fixing nitrogen, though the benefit mostly goes to the next crop, not the one beside it.
The chart
| Crop | Good neighbours | Keep apart |
|---|---|---|
| Tomato | Basil, marigold, parsley, carrot | Fennel, potato, brassicas |
| Basil | Tomato, pepper | — |
| Carrot | Onion, leek, lettuce, tomato | Dill (at flowering) |
| Onion / garlic | Carrot, beetroot, lettuce | Beans, peas |
| Beans / peas | Carrot, cucumber, radish, corn | Onion, garlic, fennel |
| Lettuce | Carrot, radish, strawberry, chives | — |
| Cabbage / brassicas | Dill, mint, rosemary, nasturtium | Tomato, strawberry |
| Cucumber | Beans, radish, dill, nasturtium | Aromatic herbs, potato |
| Pepper | Basil, tomato, onion | Fennel, beans |
| Strawberry | Lettuce, spinach, borage | Cabbage, tomato |
| Potato | Beans, corn, marigold | Tomato, cucumber, sunflower |
| Corn | Beans, squash, peas | Tomato |
| Radish | Lettuce, carrot, cucumber | — |
| Spinach | Strawberry, beans, peas | — |
| Fennel | — | Almost everything |
The one plant to keep separate
Fennel releases compounds that suppress many nearby plants. Grow it in a pot or at the end of a bed. Dill is a milder version of the same problem once it flowers.
Three pairings worth actually doing
Tomato + basil
The classic. Basil is said to confuse thrips and whitefly, and it grows well in the same conditions. Even if the pest effect is modest, it is a free second crop in space you were already watering.
Carrot + onion
The best-supported pairing in the chart. Onion scent masks carrots from carrot fly; carrot scent masks onions from onion fly. They also occupy different soil depths.
Nasturtium + brassicas
A genuine trap crop. Aphids attack the nasturtium first, and it is far easier to sacrifice than a cabbage.
Popular pairings that do not hold up
- Marigold against nematodes — only certain Tagetes species, and only when grown as a full-season green manure and dug in. A few marigolds beside tomatoes do little.
- "Nothing grows under a walnut" — true for juglone-sensitive plants, but often it is just shade and root competition.
- Specific herb-to-vegetable "friendship" lists — most trace back to one 1970s book rather than trials.
Common questions
What should you not plant next to tomatoes?
Fennel, potato and brassicas. Potato shares blight risk; brassicas compete heavily; fennel suppresses most neighbours.
Does companion planting really work?
The structural effects (shade, support, ground cover, trap crops) are reliable. Scent-based pest confusion is plausible and sometimes effective. Many specific pairings are folklore.
Can you plant herbs with vegetables?
Yes. Basil, parsley, chives and dill all work well in a vegetable bed. Keep fennel separate and let dill flower away from carrots.
What grows well with everything?
Lettuce, radish and marigold are the most flexible. They are shallow-rooted, fast and unobtrusive.
Raised bed layouts and a simple four-bed rotation that avoids these conflicts: 5 Minute Garden.
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