🌿 Companion Planting Reference
Select a vegetable to see traditionally recommended companion plants (that help it thrive) and plants commonly advised against planting nearby.
Where these lists come from
This is a lookup, not a calculation. Ten crops each carry a fixed pair of lists drawn from traditional companion planting practice, and picking a crop simply prints them. The pairings run both ways where both plants are on the menu — tomatoes and corn warn about each other — but many partners named, such as basil, dill, marigold, strawberries and potatoes, are not themselves selectable.
Some of the entries have a mechanism behind them and some are inherited folklore. It is worth knowing which is which:
| Pairing | What is behind it |
|---|---|
| Corn, beans and squash | Structural: corn is the trellis, squash shades out weeds. The nitrogen beans fix mostly benefits the following crop. |
| Tomatoes away from corn | Shared pest. The corn earworm and the tomato fruitworm are the same insect, Helicoverpa zea. |
| Marigold with squash or tomatoes | French marigold roots release α-terthienyl, which suppresses root-knot nematodes — but only from a dense planting held for a season. |
| Fennel away from almost everything | Its root exudates inhibit the germination and growth of neighbouring plants. |
Using it without over-trusting it
Treat the good list as a planting suggestion and the bad list as the more useful half: crop-family clashes and heavy shade or root competition are real and repeatable, while claims that one plant repels another's pests are mostly untested.
Frequently asked questions
What should not be planted next to tomatoes?
The list here is brassicas, fennel and corn. Brassicas are heavy feeders that compete hard, fennel suppresses its neighbours, and corn shares a caterpillar pest with tomato fruit.
Why plant basil with tomatoes?
Traditionally for flavour and to deter pests, though the pest claim has little trial support. The practical case is simpler: both want the same sun, warmth and watering, and basil fits the gaps between staked plants.
Do onions really harm beans?
It is one of the oldest entries in companion lore and one of the least evidenced. Alliums are thought to affect the rhizobia that let beans fix nitrogen, but garden results are inconsistent.