Companion Planting Guide for UK Vegetable Gardens
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Grow healthier, more productive vegetables by planting the right crops together. Companion planting is nature's way of pest control, pollination, and space optimization.
What is Companion Planting?
Companion planting is the practice of growing certain plants together for mutual benefit. Some plants help each other by repelling pests, attracting beneficial insects, improving soil, or providing physical support. Others compete for resources and should be kept apart.
Benefits of Companion Planting:
- Natural pest control: Some plants repel pests that attack their neighbors
- Attract beneficial insects: Flowers attract pollinators and predatory insects
- Maximize space: Tall and short crops can share the same bed
- Improve soil: Legumes fix nitrogen for heavy feeders
- Provide support: Sturdy plants can support climbing crops
Classic Companion Planting Combinations
The Three Sisters
Sweetcorn + Climbing Beans + Squash
- Sweetcorn provides support for beans to climb
- Beans fix nitrogen in soil for corn and squash
- Squash leaves shade soil, suppress weeds, retain moisture
Tomatoes + Basil
Basil repels aphids and whitefly from tomatoes.
Carrots + Onions
Onions repel carrot fly, while carrots repel onion fly.
Lettuce + Radishes
Fast-growing radishes mark rows of slow-germinating lettuce and are harvested before lettuce needs the space.
Brassicas + French Marigolds
Marigolds repel cabbage white butterflies and other brassica pests.
Companion Planting Chart
Tomatoes
Good companions: Basil, carrots, onions, parsley, marigolds, nasturtiums
Avoid: Brassicas, potatoes, fennel
Carrots
Good companions: Onions, leeks, rosemary, sage, peas, lettuce, radishes
Avoid: Dill, parsnips
Beans (Runner & French)
Good companions: Sweetcorn, squash, cucumbers, potatoes, carrots
Avoid: Onions, garlic, fennel
Potatoes
Good companions: Beans, peas, brassicas, marigolds, nasturtiums
Avoid: Tomatoes, cucumbers, squash
Brassicas (Cabbage, Kale, Brussels Sprouts)
Good companions: Onions, garlic, beets, celery, potatoes, marigolds
Avoid: Tomatoes, peppers, strawberries
Peas
Good companions: Carrots, turnips, radishes, cucumbers, beans, potatoes
Avoid: Onions, garlic
Beneficial Flowers for the Vegetable Garden
French Marigolds (Tagetes patula)
Repel aphids, whitefly, and cabbage white butterflies. Plant throughout the vegetable garden.
Nasturtiums
Act as a trap crop for aphids and cabbage white butterflies.
Borage
Attracts bees for pollination. Excellent near squash, cucumbers, and beans.
Frequently Asked Questions
What plants grow well with tomatoes?
Basil, carrots, onions, parsley, marigolds and nasturtiums all grow well with tomatoes. Basil in particular helps repel aphids and whitefly. Avoid planting tomatoes near brassicas, potatoes or fennel, which compete for the same nutrients or share blight risk.
Do beans fix nitrogen?
Yes. Beans, peas and other legumes host nitrogen-fixing bacteria in root nodules that convert atmospheric nitrogen into a form plants can use. This is why beans work so well alongside sweetcorn and squash in a Three Sisters planting — the beans feed the soil that the other two crops draw on. Leave the roots in the ground after harvest rather than pulling them up, so the fixed nitrogen stays in the bed for the next crop.
Which plants repel pests?
French marigolds repel aphids, whitefly and cabbage white butterflies and are worth planting throughout a vegetable garden. Basil repels aphids and whitefly specifically around tomatoes. Onions and carrots planted together each repel the fly that targets the other (onion fly and carrot fly). Nasturtiums act as a trap crop, drawing aphids and cabbage white butterflies away from your vegetables rather than repelling them outright.
Learn More
What the evidence says
Many companion pairings are tradition rather than tested results. Some are backed by research; most have not been tested in the trusted sources we checked. Growing a mix of plants rather than one crop can lower pest pressure in general.
| Pairing or claim | Status | What the sources say |
|---|---|---|
| French or African marigolds against root-knot nematodes | Supported, with a catch | They work as a cover crop grown before the vegetable crop and dug in; planting them alongside the crop does not. |
| French marigolds next to tomatoes against glasshouse whitefly | Some evidence | A Newcastle University glasshouse trial (2019) found marigolds slowed whitefly build-up on tomatoes; the RHS cites it, and notes that mixing tomatoes with other plants had a similar effect. |
| Marigolds repel insects in general | Not supported | LSU AgCenter: research does not substantiate the claims, and there is no real benefit for repelling insects. |
| Nasturtiums lure caterpillars and blackfly away from crops | Tradition | The RHS: supported by anecdotal evidence from some gardeners; scientific evidence remains limited. Nasturtiums host blackfly themselves. |
| Tomatoes + basil; carrots + onions; brassicas + French marigolds; the Three Sisters | Tradition | Not tested in the sources we checked. Grow them if you like them, but do not rely on them for pest control. |
For the pests themselves, see aphids, carrot fly and cabbage caterpillars; crop guides: tomatoes, carrots, onions, cabbage, runner beans, sweetcorn, squash.
References
- Newcastle University (Conboy et al., PLOS ONE, 2019): Companion planting with French marigolds protects tomato plants from glasshouse whiteflies
- RHS: Three ways to use companion planting
- LSU AgCenter: Marigolds may help control some nematodes
- RHS: How to grow annual nasturtiums
- University of Arizona Cooperative Extension: Companion planting
- UF/IFAS Extension: Marigolds (Tagetes spp.) for nematode management (ENY-056/NG045)
Each statement in the sections above is supported by at least three of these sources, unless it names the single study or table it comes from. Sources checked 24 October 2026.
Build The Plan Into Your Garden
Planning guides are easier to act on when the dates, beds and crop records live in one place.
Keep going
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.