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Companion planting means growing plants together for a useful purpose, such as sharing space, providing shelter or supporting insects that benefit the garden. Some combinations have evidence for particular pest effects, but a universal chart of plant “friends” and “enemies” cannot predict results in every bed.
Start with a clear job for the pairing. “Harvest a quick crop before the larger one needs the space” is something you can plan and observe. “Make everything grow better” is rather harder to measure.
Three useful reasons to combine plants
Use space at different times
A quick crop can occupy space that a slower crop will need later. The important part is harvesting the first crop in time. Mature spacing still matters, even when the bed looks empty on planting day.
Manage shade and shelter
A taller crop may provide useful summer shade, but it can also take light from a plant that needs it. Check the direction of the sun and the season. Our guide to vegetables in partial shade helps distinguish useful shade from too little light.
Provide flowers and habitat
Flowers around the vegetable patch can provide resources for insects. Choose plants suited to the site and leave room to maintain the crops. A varied garden can support wildlife without promising that every insect will stay away from your lettuce.
The RHS companion-planting guide discusses space use, support and pest effects, while stressing that results depend on the combination and circumstances.
Practical pairings to consider
| Combination | Useful purpose | What to watch |
|---|---|---|
| Quick salads between slower crops | Harvest something before the main crop fills the space | Remove the early crop before competition becomes a problem |
| Tomatoes and basil in adjacent containers | Convenient harvests for the kitchen | Give each enough light and root space; do not assume a flavour boost |
| Flowering plants around vegetable beds | Add floral resources and diversity | Keep access and crop spacing clear |
| French marigolds with greenhouse tomatoes | A specific whitefly-management approach worth understanding | Evidence does not make marigolds a general pest shield |
Adjacent pots can be a useful compromise. You can move or remove one plant if it starts crowding another. Our plant pot size guide helps you plan enough root space.
What does the marigold evidence actually show?
A controlled study of French marigolds and greenhouse whitefly found a protective effect when marigolds were grown alongside tomatoes from early in the crop. Introducing them after a heavy infestation had developed gave much less benefit.
That is evidence about particular plants, an insect and growing conditions. It does not establish that any marigold will repel slugs, protect every crop or rescue an already damaged bed. Our pest-repellent plants guide looks at those claims separately.
Popular claims to treat cautiously
Tomatoes and basil are lovely together on a plate, but do not promise that neighbouring basil will improve tomato flavour. Similarly, strong-smelling plants should not be your only protection against a pest with a history of damaging a crop.
Do not treat a row of peas or beans as an instant fertiliser supply for everything beside it. Plan soil care and feeding around the crop’s needs rather than a companion chart. For the starting conditions, see how to prepare allotment soil.
Different root depths do not eliminate competition. Plants still share light, water and space. If a pairing leaves one crop crowded, shaded or difficult to water, change the arrangement.
Try one pairing without risking the whole bed
- Name the goal. Decide whether you want better use of space, flowers nearby or a specific effect you can check.
- Draw mature plants. Mark their final size, supports and your access route.
- Keep the trial small. Use one section rather than redesigning the entire plot.
- Keep notes. Record planting and harvest dates, crowding, pest damage and weather.
- Compare cautiously. A better year may reflect weather or timing as well as the companion plant.
If you can, grow a similar small area without the companion. It will not be a laboratory trial, but it can help you avoid crediting the pairing for every change.
When to simplify
Companion planting should not make routine care harder. If harvesting becomes awkward, labels disappear under foliage or watering misses the root zone, use fewer plants. Separate containers, a flower border beside the vegetables or a simple sequential planting plan may serve you better.
For a new garden, choose useful crops and manageable spacing first with our kitchen garden starter guide. Add a companion when you can explain what it is meant to do. A workable garden does not need a complicated relationship chart.
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Reviewed and updated October 2026. By Niki Wilkinson, Back To The Good Life.
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