Co Planting Chart

Companion planting is the practice of growing plants near each other because they are thought to help one another — by deterring pests, attracting pollinators, sharing space well or using nutrients differently. Pick the plants for a bed and this chart shows their traditional friends and foes, flags any pairs best kept apart, and suggests companions to add.

How companion planting is thought to work

The Three Sisters

The best-known companion system is the Three Sisters, developed by Indigenous peoples of the Americas: corn, beans and squash grown together. The corn provides a pole for the beans, the beans add nitrogen to the soil, and the broad squash leaves shade the ground, keeping moisture in and weeds down. Together they also make a nutritionally complementary diet. Plant the corn first, then the beans when the corn is about 15 cm tall, and the squash around the edges.

How to use the checker

1. Tick the plants you plan to grow in one bed or container.
2. Read the good pairings already in your selection.
3. Check the pairs to keep apart and move one of them to another bed.
4. Look at the suggested companions — plants that go with several of your choices without clashing.
5. Print the bed plan and keep it with your garden notes.

Your selection is remembered in this browser for next time.

Worked example

A gardener plans a bed with tomatoes, basil, carrots and onions. The checker finds good pairings — tomato with basil, carrot and onion, and carrot with onion — and no clashes. It suggests further companions such as marigolds, lettuce, chives and parsley. When they add potatoes, it flags tomato ✗ potato — both are prone to blight, so keeping them apart reduces the spread of disease — and they move the potatoes to another bed.

Plants commonly kept apart

• Tomatoes and potatoes — share blight and other diseases.
• Beans and onions or garlic — alliums are said to stunt beans.
• Brassicas and strawberries — traditional advice to separate them.
• Fennel and most vegetables — fennel is often grown on its own.
• Dill and carrots — close relatives that can cross-pollinate and share pests.
• Cucumbers and potatoes — potatoes are thought to make cucumbers more prone to blight.

What the evidence says

Some companion effects are well supported: trap crops, flowering strips that boost beneficial insects, and legumes that fix nitrogen. Many other pairings come from tradition and gardeners’ experience rather than controlled trials, and results vary with climate, soil and pest pressure. Good spacing, crop rotation, healthy soil and choosing resistant varieties usually matter more than any single pairing.

Crop rotation

Rotate crop families to different beds each year so soil-borne pests and diseases don’t build up — for example legumes, then brassicas, then roots, then solanaceous crops (tomatoes, potatoes, peppers). Companion planting fits inside a rotation plan: choose companions for each bed as the main crop moves around the garden.

Herbs and flowers that earn their place

Letting a few herbs flower rather than picking every stem gives beneficial insects a food source through the season.

Spacing still matters

Companions only help if each plant has room to grow. Follow the spacing on seed packets, remember how big plants will be at full size, and give sprawling crops such as squash and pumpkins plenty of room. Tall crops like corn and staked tomatoes cast shade, so plant sun-loving companions on their sunny side and shade-tolerant ones such as lettuce behind them.

Planning a companion bed step by step

1. Choose one or two main crops for the bed.
2. Check their friends and foes in the chart.
3. Add a flowering companion or two for insects, along the edges or at the ends.
4. Fill gaps with fast crops such as radishes or lettuce that are harvested before the main crop needs the space.
5. Keep plants that should stay apart in different beds or at least a metre away.
6. Note what worked at the end of the season.

Small spaces and containers

On a balcony, pair a tomato with basil and a French marigold in a large pot, or grow lettuce around the base of taller plants. Herbs like chives and thyme fit into gaps and bring flowers for pollinators. Make sure every plant still gets enough light and water — crowding cancels out any benefit.