Companion Planting Guide for UK Gardens: Grow More by Growing Together

Companion planting is one of those time-honoured techniques that every experienced grower swears by — and for good reason. By placing certain plants together strategically, you can naturally deter pests, attract beneficial insects, improve soil fertility, and even boost yields. Best of all, it costs nothing and requires no chemicals.

If you are planning your beds this spring, now is the perfect moment to think about which plants will grow well side by side. Here is a practical guide to the best companion pairings for UK gardens.

What Is Companion Planting?

Companion planting is simply the practice of growing different species close together for mutual benefit. The relationship can work in several ways:

Pest deterrence — some plants emit scents that confuse or repel insects

Pest attraction — "trap crops" lure pests away from your main crop

Pollinator attraction — flowers draw bees and hoverflies, improving vegetable yields

Nutrient fixing — legumes such as peas and beans fix nitrogen into the soil, feeding neighbouring crops

Physical support — tall plants can shelter more tender neighbours from wind or excessive sun

No single combination works as a silver bullet, but thoughtful pairing can significantly reduce the need for intervention throughout the season.

Classic Companion Planting Combinations

Tomatoes + Basil

This is perhaps the most famous combination in the kitchen garden. Basil is widely believed to repel aphids and whitefly from tomatoes, whilst also attracting pollinators that improve fruit set. Planted between your tomato rows or at the base of grow-bags, it also makes harvesting dinner rather convenient.

Carrots + Onions (or Chives)

Carrot fly and onion fly are both significant pests in the UK. Conveniently, their respective scents confuse each other's pest. Plant rows of carrots and onions alternately, or edge your carrot bed with chives. The mixed scent cloud makes it harder for female carrot flies to locate their target.

Brassicas + Nasturtiums

Nasturtiums act as a magnet for aphids and cabbage white caterpillars, drawing them away from your cabbages, kale, and broccoli. Plant a row of nasturtiums at the border of your brassica bed and inspect them regularly — when they are covered in aphids, you know your brassicas are being spared. Nasturtiums are also edible, producing peppery flowers and leaves that are wonderful in salads.

Courgettes + Borage

Borage is a fast-growing herb with striking blue flowers that bees adore. Planted among your courgettes, it improves pollination and is said to deter tomato hornworm. The large leaves of courgette plants also provide shade that suppresses weeds around the borage stems, making this a tidy pairing.

Runner Beans + Sweet Corn + Squash

Known as the "Three Sisters," this combination originated with indigenous North American growers and works beautifully in UK kitchen gardens too. Corn provides a vertical support for beans to climb. Beans fix nitrogen, feeding the hungry corn and squash. Squash spreads along the ground, suppressing weeds and retaining soil moisture with its large leaves. Together, the three make efficient use of every inch of space.

Roses + Garlic

If you grow roses in a mixed garden, plant garlic cloves around their base in autumn. Garlic is a natural fungicide and is believed to deter aphids and blackfly. It also helps suppress black spot fungal disease on rose leaves.

Lettuce + Tall Vegetables

Lettuce bolts quickly in hot sun. Planting it in the partial shade of taller crops — sweetcorn, climbing beans, or even fennel — extends its season and reduces the need for watering. This is particularly useful for summer sowings from June onwards.

Combinations to Avoid

Not all neighbours are beneficial. Some plants actively inhibit each other:

Fennel + Almost Everything — fennel is allelopathic, meaning it releases chemicals that suppress the growth of most vegetables. Keep it at the edge of the garden, well away from your main beds.

Onions + Peas or Beans — alliums are thought to inhibit the growth of legumes, so keep them in separate beds.

Brassicas + Brassicas — this is not companion planting, but it is worth noting: never follow one brassica crop with another in the same bed. Rotate crops to prevent clubroot and other soil-borne diseases building up.

Using Flowers for Biodiversity

Incorporating flowers into your vegetable garden is one of the highest-impact things you can do. Even a few pots of flowering plants at the edges of beds can dramatically increase beneficial insect activity.

Good choices for UK kitchen gardens include:

Marigolds (Tagetes) — repel whitefly and aphids; the roots exude a chemical that deters soil nematodes

Phacelia — one of the best bee plants; fast-growing and easy to sow directly

Poached egg plant (Limnanthes douglasii) — beloved by hoverflies, whose larvae eat aphids

Sweet alyssum — low-growing, long-flowering, and a favourite of parasitic wasps that prey on caterpillars

Sow a scatter of mixed wildflower seeds in any unused corners and let them do the work.

Getting Started This Spring

The simplest way to begin is to pick one or two pairings and observe the results. Start with tomatoes and basil — two plants most UK gardeners grow anyway — and note whether you see fewer aphids than in previous years.

Keep a simple garden diary. Companion planting works best when you build up observations over several seasons, learning which combinations thrive in your specific microclimate and soil conditions.

Talk to neighbours. Your street is a living laboratory. Comparing notes on what pest problems you have seen — and what seems to help — is exactly the kind of knowledge sharing that makes community growing so valuable.

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Looking to connect with other growers in your neighbourhood and share what's working in your garden? Join Locavori to swap tips, share surplus produce, and discover what your neighbours are growing this spring.