Companion Planting for Healthier Garden Vegetables

Why Companion Planting Earns Its Place

There is something quietly satisfying about a vegetable bed that looks a little untidy to the passer-by — a frill of calendula along the carrot row, a pot of mint tucked by the path — yet works harder because of it. Companion planting is simply the practice of choosing neighbours with intention. Some plants mask the scent that pests use to find their dinner. Some offer food and shelter to the hoverflies, ladybirds and lacewings that do your policing for you. Others make better use of the ground by growing at different heights or at different times of year.

It is worth saying plainly: companion planting is not a substitute for good soil, sensible crop rotation and a bit of netting. Treat it as the layer on top — the bit that makes the whole plot more resilient, more colourful and considerably more pleasant to spend time in.

Flowers That Do the Heavy Lifting

If you only add one thing this season, add flowers. They bring in pollinators, which matters enormously for runner beans, courgettes and tomatoes, and they support the predatory insects that keep aphids in check.

• French marigolds (Tagetes) — short, cheerful and genuinely useful. Grow them among tomatoes and around the base of brassicas. Their roots release compounds that suppress soil nematodes, and the flowers attract hoverflies.
• Calendula — hardy, self-seeding and long-flowering, filling the hungry gap in early summer when little else is open. Excellent anywhere you have bare earth.
• Nasturtiums — the great sacrifice plant. Blackfly and cabbage white butterflies will choose them over your broad beans and kale, so plant them a metre or so from your crops, not touching them.
• Borage — a magnet for bees, and a good partner for strawberries and tomatoes. The blue flowers taste faintly of cucumber in a jug of water.
• Sweet alyssum — low-growing and frothy, ideal for carpeting the ground beneath brassicas where hoverflies patrol.

Herbs as Hard-Working Neighbours

Herbs earn their keep twice over: they confuse pests, and they are within arm's reach of the kitchen door.

• Chives and garlic chives — plant generously along carrot and parsnip rows. Their strong scent disrupts carrot fly, and the purple flowers are loved by bees.
• Basil — the classic tomato companion. Grow a few plants among the tomatoes in the greenhouse, where the warmth suits both.
• Mint — brilliant for hoverflies, but keep it firmly in a pot sunk into the ground or the runners will take the bed.
• Rosemary, sage and thyme — evergreen, drought-tolerant and useful as low hedging around raised beds, where their scent works on the breeze.
• Coriander — let a plant or two run to flower. The umbels are irresistible to small parasitic wasps that prey on caterpillars.

Vegetables That Grow Well Together

• Carrots and onions or leeks — the oldest pairing in the book. Each masks the other's scent, so carrot fly and onion fly both struggle to find home.
• Beetroot and onions — beetroot grows happily in the gaps, and the alliums seem to keep leaf miners at bay.
• Radishes between slow rows — sown with parsnips or carrots, they mark the row while you wait for germination, and are pulled before the roots need the space.
• Lettuce in the shade of sweetcorn or tall brassicas — a little dappled shade keeps lettuce from bolting in a hot July.
• Peas with spinach — the peas climb, the spinach shelters at their feet and crops before the pods are ready.

Making Better Use of Space

A British growing season is short, so stacking crops is where companion planting pays most obviously. Think in three layers: something tall and climbing, something round and leafy in the middle, and something low and quick at ground level. A wigwam of runner beans with lettuce underneath and radishes at the edge will crop from May to October from a single square metre.

Legumes are the other quiet gift here. Peas and beans fix nitrogen in nodules on their roots, so follow them with hungry leafy crops — cabbage, chard, spinach — rather than clearing the ground bare. Leave the roots in when you cut the stems down, and the following crop gets the benefit.

What to Keep Apart — and What Not to Expect

Some plants simply do not get on. Keep these apart:

• Onions, garlic and leeks away from beans and peas — alliums inhibit the bacteria that legumes rely on to fix nitrogen.
• Fennel away from almost everything — it releases compounds that suppress neighbouring plants. Grow it in a pot on the patio.
• Potatoes away from tomatoes — both carry blight, and once it arrives in a wet August it will sweep through the pair.
• Dill away from carrots — they belong to the same family, share pests and will cross-pollinate if you save seed.

And do check your trap crops every few days. A nasturtium smothered in blackfly stops being a decoy and becomes a nursery; cut the worst of it off and drop it in the council green bin rather than the compost heap. That ten minutes of wandering with a mug of tea, pinching off flowers, watching the hoverflies hover — that is the part of companion planting that does as much for the gardener as for the garden.