Good companions
Bad companions
Companion Planting Guide
Look up which plants grow well together and which should be kept apart. Companion planting uses plant relationships to improve growth, deter pests, and attract beneficial insects.
Classic companion combinations
| Plant | Good companions | Bad companions |
|---|---|---|
| Tomatoes | Basil, carrots, marigolds, parsley | Fennel, brassicas, kohlrabi |
| Carrots | Rosemary, sage, onions, leeks | Dill, parsnips |
| Beans (pole) | Corn, squash, nasturtium | Onions, garlic, fennel |
| Basil | Tomatoes, peppers, oregano | Sage, thyme |
| Brassicas | Dill, chamomile, mint | Tomatoes, strawberries |
The Three Sisters
A classic Native American companion planting system: corn provides structure for beans to climb; beans fix nitrogen for the corn and squash; squash leaves shade the soil to retain moisture and suppress weeds. Each benefits the others.
Flowers as companions
- Marigolds: repel nematodes and aphids; attract pollinators
- Nasturtiums: trap crop for aphids; edible flowers
- Borage, deters tomato hornworm; attracts bees
UK allotment companion planting: practical classics
The UK has over 330,000 registered allotment holders. The allotment tradition, dating from the 19th century, has developed its own body of companion planting knowledge:
- French marigolds (Tagetes patula) with tomatoes, the most widely practised UK companion planting. Marigolds repel whitefly, a serious problem in UK polytunnels and glasshouses. Plant densely around tomato bases and inside greenhouse beds.
- Leeks with carrots, leek smell confuses carrot root fly (Psila rosae), one of the most destructive UK vegetable pests. Interplanting rows reduces attack significantly.
- Nasturtiums as a sacrificial crop, plant around brassicas to draw blackfly (Aphis fabae) and caterpillars away from the main crop. RHS recommended.
- Chives under apple trees, said to reduce apple scab incidence; also practical under rose bushes for aphid deterrence.
The RHS (Royal Horticultural Society) maintains a database of pest-resistant cultivars at rhs.org.uk, a useful starting point before selecting companion plants.
UK-specific pests and their plant deterrents
| UK pest | Companion deterrent | Notes |
|---|---|---|
| Carrot root fly | Leeks, onions, rosemary | Interplant or use as a barrier around carrot rows |
| Whitefly (glasshouse) | French marigolds | Most effective under glass; plant densely |
| Cabbage white butterfly | Nasturtiums, mint, thyme | Sacrificial nasturtiums redirect egg-laying |
| Slugs | No reliable plant deterrent | Use copper barriers, nematodes (Phasmarhabditis) or hand-pick at night |
| Allium leaf miner | No proven companion | Physical fleece barrier most effective |