Companion Planting: The Complete Guide

Companion planting is one of the oldest tricks in the vegetable garden — and one of the most rewarding. When you put the right plants next to each other, they help each other grow: deterring pests, attracting pollinators, improving the soil, and even making the harvest taste better. Done well, it means fewer problems, less work, and bigger yields, all without reaching for a single chemical spray.

This guide walks through how companion planting works, the pairings that consistently deliver, the combinations to avoid, and how to lay out your beds so everything thrives together.

Why companion planting works

Plants are not passive — they release chemicals, attract insects, cast shade, and shape the soil around them. Companion planting uses those interactions deliberately.

The main mechanisms are:

Pest confusion. Strong-smelling herbs and flowers mask the scent of a target crop so pests struggle to find it.

Trap cropping. A sacrificial plant lures pests away from the one you want to harvest.

Beneficial insect attraction. Flowers bring in hoverflies, lacewings, ladybugs/ladybirds, and parasitic wasps that eat aphids, caterpillars, and whitefly.

Nitrogen fixation. Legumes (beans, peas) host bacteria on their roots that pull nitrogen from the air into the soil — a free fertiliser for hungry neighbours.

Living mulch and shade. Sprawling plants like squash shade the soil, keeping it cool and moist and crowding out weeds.

Vertical layering. Tall plants give climbers a structure to grow up, while low ground-cover plants fill the space below.

You don't need to use every mechanism. Even one or two well-chosen pairings will lift the whole garden.

The classic combinations that work

These pairings have been tested by generations of growers and back up well in trial data.

Tomatoes + basil + marigolds

Basil is widely reported to deter whitefly and tomato hornworm, and many gardeners swear it improves tomato flavour. Marigolds (especially *Tagetes patula*) release compounds from their roots that suppress root-knot nematodes. Plant 2–3 basil plants and a ring of marigolds around each tomato.

The Three Sisters: corn, beans, squash

The classic Indigenous American polyculture. Corn provides a pole for beans to climb, beans fix nitrogen for the corn and squash, and squash leaves shade the soil and deter raccoons and other pests. Plant corn first; once it's 15 cm (6 in) tall, sow beans at the base and squash between the corn blocks.

Carrots + onions (or leeks)

Carrots are plagued by carrot fly; onions and leeks by onion fly. Each plant's scent masks the other from its pest. Alternate rows of carrots and onions for protection in both directions.

Lettuce + radishes + carrots

A space-saving trio. Radishes germinate in 4–5 days and are harvested in 25–30 days, loosening the soil for the slower carrots. Lettuce fills the gaps and provides cooling ground cover. All three can share a 30 cm (12 in) wide row.

Cucumbers + nasturtiums + dill

Nasturtiums act as a trap crop for aphids, drawing them away from cucumbers. Dill brings in predatory insects that eat cucumber beetles. Both flowers also draw pollinators.

Brassicas (cabbage, kale, broccoli) + dill + nasturtiums

Cabbage white butterflies are the bane of brassicas. Nasturtiums lure them away and dill attracts the wasps that parasitise their caterpillars. Sage and thyme planted nearby also help.

Strawberries + borage

Borage flowers attract pollinators and the plant is said to improve strawberry flavour and yield. Bonus: borage flowers are edible and taste of cucumber.

Pairings to avoid

Some plants don't get along.

Tomatoes and brassicas — they compete heavily and brassicas can stunt tomato growth.

Onions/garlic and beans/peas — onion family plants release sulphur compounds that suppress legume root bacteria, reducing nitrogen fixation.

Fennel and almost everything — fennel releases growth-inhibiting compounds. Grow it in its own pot or corner.

Potatoes and tomatoes — same family, same diseases (especially blight). Keep them apart.

Cucumbers and sage — sage's strong aromatic oils can stunt cucumber growth.

Flowers earn their place

If you have to choose one habit that transforms a vegetable garden, plant flowers among your crops. The best workhorses:

Marigolds — nematode suppression, whitefly deterrent.

Nasturtiums — aphid trap crop, edible flowers and leaves.

Calendula — attracts hoverflies, edible petals, self-seeds happily.

Borage — pollinator magnet, said to improve flavour of nearby fruit.

Phacelia — one of the best bee plants you can grow; also a great green manure.

Alyssum — low ground cover that brings in hoverflies whose larvae devour aphids.

Aim for at least 10–15% of your growing space to be in flower at any one time during the season.

How to design a companion-planted bed

A simple, practical approach:

1. Anchor with the main crop — the vegetable you most want to harvest from this bed. 2. Add a pest-repelling herb or allium — basil, dill, chives, onions. 3. Edge with flowers — marigolds, calendula, or alyssum along the front and corners. 4. Tuck in a quick crop — radishes, lettuce, or rocket/arugula in the gaps. 5. Add a nitrogen fixer where appropriate — beans or peas in or near the bed if the soil needs feeding.

Keep blocks small. Companion planting works best when species are interplanted, not separated into long monoculture rows. A 1.2 × 1.2 m (4 × 4 ft) bed with five or six different plants will outperform a single-species row of the same size.

Watch and adjust

Every garden is different. Soil, climate, and the specific pests in your area all change what works best. Try a few combinations this season, take notes, and refine next year. Within two or three seasons you'll have your own list of pairings that work brilliantly for your patch.

Check your local last-frost date before planting warm-season crops, and remember that Southern Hemisphere readers should flip the timing — the principles stay the same.

Grow alongside your neighbours

Companion planting also works between gardens. A few rows of marigolds in your yard help the neighbour two doors down whose tomatoes are full of whitefly. Locavori is built for exactly this — sharing produce, seeds, and growing know-how with the people around you, so your whole street ends up with healthier gardens and fuller harvest baskets.

Join Locavori free → and start growing better food with your neighbours.