What is companion planting?
Companion planting is the practice of growing different plants close together because they benefit each other in some way. The benefits are varied: some plants deter the pests that trouble their neighbours, others fix nitrogen from the air into the soil, and some simply make better use of available space by growing at different heights or speeds.
The science behind some companion planting relationships is well-established. Others are based on long gardening tradition and observation, and while the mechanisms are less clear, the practice is widely used and broadly consistent with organic principles. We include both, and say so where the evidence is stronger or weaker.
You can also see companion planting information for each plant individually by clicking any crop in the Crops page and scrolling to the companion planting section of its guide.
Deterring pests naturally
One of the most useful roles a companion plant can play is masking or disrupting the signals that pests use to find their preferred crop.
Garlic is one of the most versatile pest-deterring companions in the kitchen garden. Planted near tomatoes, courgettes, lettuce, kale, or strawberries, it is thought to deter aphids and spider mites with its strong scent. It is low-growing, unobtrusive, and planted in autumn when other crops have cleared the ground, so it rarely competes for space.
Basil planted alongside tomatoes or chillies is thought to deter aphids and whitefly. Both crops need the same warm, sheltered conditions, so they suit the same spots naturally, a greenhouse, a bright windowsill, or a sheltered container on a south-facing wall.
Mint placed near kale can help deter cabbage white butterflies, which lay the eggs that hatch into the caterpillars that cause serious damage to brassica leaves. Mint spreads aggressively underground, so always grow it in a container rather than directly in the ground, then position the pot close to the kale plants where its scent can do its work.
Radishes act as a trap crop alongside lettuce. Flea beetles, which create tiny holes in the leaves of many brassicas and salad crops, have a strong preference for radish leaves. Sowing a row of radishes among your lettuce draws the beetles onto the radishes and largely away from the crop you care more about. As a fast-growing plant, the radishes are usually harvested and gone before they have suffered much real damage themselves.
Fixing nitrogen for hungry neighbours
Legumes, the plant family that includes peas and runner beans, have a remarkable ability to fix nitrogen from the air and store it in nodules on their roots. When the roots break down in the soil, that nitrogen becomes available to nearby plants. Nitrogen is the nutrient that drives leafy, vegetative growth, so leafy crops like lettuce benefit most directly.
Growing peas or runner beans alongside lettuce, courgettes, or other hungry crops makes practical sense. At the end of the season, cut the legume stems off at ground level but leave the roots in the soil: as they break down over winter, they release stored nitrogen that will feed whatever follows in that bed.
This is the logic behind the traditional Three Sisters planting, where beans, squash, and a third crop (traditionally sweetcorn) are grown together. The beans fix nitrogen for the squash. A simplified version, peas or runner beans growing alongside courgettes, works well in smaller spaces.
Making better use of space
In a small growing area, fitting more into the same space without crowding is genuinely useful. Companion planting offers two main approaches.
Underplanting means growing a low, spreading crop beneath a taller one. Lettuce grows well beneath tomatoes, using ground-level space that would otherwise be unused. The tomato foliage provides welcome shade that slows the bolting that spoils lettuce flavour in summer. Lettuce also works as an underplanting between strawberry plants, where it suppresses weeds and helps retain soil moisture.
Succession planting with quick crops means sowing a fast-growing plant in the same space as a slower one, harvesting it before the slower crop needs the room. Radishes are the classic example: sown between young pea plants or at the base of runner beans, they are harvested within 4 to 6 weeks and gone before the main crop fills the space. This approach extracts a harvest from ground that would otherwise be empty.
Plants to keep apart
Not all plant combinations are beneficial. A few pairings are worth avoiding.
Garlic and other alliums near peas or runner beans. Alliums including garlic are thought to inhibit the root nodules through which legumes fix nitrogen from the air. Since nitrogen-fixing is one of the main reasons to grow legumes in the first place, planting garlic nearby undermines that benefit. Keep them on opposite sides of the growing area.
Strawberries near kale and other brassicas. Strawberries and brassicas are generally considered poor companions. Some sources suggest brassicas can inhibit strawberry growth, and the two groups also have different watering and feeding requirements, which makes them harder to manage well side by side.
Putting it into practice
You do not need to plan your entire growing space around companion planting to benefit from it. A few easy pairings go a long way:
- Push a garlic clove between your strawberry plants in autumn. It costs almost nothing and the timing fits naturally with when garlic goes in anyway.
- Sow a short row of radishes between your lettuce seedlings. They will be harvested within a month and the flea beetle control is genuinely useful.
- Grow basil in the same pot or greenhouse space as your tomatoes or chillies. They share the same warm conditions and the deterrent effect is a bonus.
- Keep a pot of mint near your kale, but not in the ground. The scent does the work without the roots taking over.
- At the end of the season, leave legume roots in the soil rather than pulling them. The nitrogen stored in the nodules feeds the soil for whatever grows there next.
For each plant in our library, the companion planting section in its crop guide lists which plants it grows well with and which to avoid, along with the specific reason for each. Open any plant on the Crops page to see this information.