Basil, marigolds and garlic beside tomatoes, but never potatoes

Basil, French marigolds, garlic, chives, parsley and carrots all grow well next to tomatoes, and flowers such as calendula, borage, cosmos and zinnias earn their place by bringing in pollinators and aphid-eaters. The one neighbour to avoid above all is the potato. Sweetcorn and Florence fennel are also best kept elsewhere.

Our companion planting checker lists every neighbour for tomatoes and the rest of your plan, and flags any pair in a bed that clashes.

Good neighbours for tomatoes

Plant	Why it’s there
Basil	Likes the same warmth, sun and watering, and fits in the gaps between plants. Often said to help flavour, which is hard to prove
French marigold	Widely grown to deter whitefly, especially in greenhouses, and a magnet for hoverflies
Garlic and chives	Upright, narrow, and take little room. Their scent is thought to confuse some pests
Parsley	Low and leafy, and when left to flower it feeds hoverflies and small wasps
Carrot	Roots at a different depth, so they share the ground without competing much
Calendula, borage, cosmos, zinnia	Flowers that keep pollinators and predatory insects around the plot
Asparagus	Tomatoes are a traditional companion in the asparagus bed, planted alongside the crowns in summer

Most of these are low or upright plants that fit under or between tomatoes without shading them. That’s half of good companion planting: putting plants together that use different space.

What not to plant next to tomatoes

Potatoes. This is the one that matters. Potatoes and tomatoes are in the same family and both catch late blight, the disease that turns leaves and fruit brown in a wet summer. Blight spores travel from one to the other, so a potato row next to the tomatoes makes an outbreak more likely and faster. Keep them as far apart as your plot allows, and don’t follow one with the other in the same bed.

Sweetcorn. Tall and hungry, it shades tomatoes, and the two compete hard for water and food. Both also share a pest in warmer countries, the corn earworm.

Florence fennel. It’s often listed as a poor neighbour for most crops, tomatoes included, and it’s easier to give it a row of its own.

Raspberries and blackberries. Cane fruit can carry verticillium wilt, a soil disease that also attacks tomatoes. It’s sensible not to plant tomatoes where cane fruit grew.

Planting the neighbours without crowding

Tomatoes need about 45 cm between plants and 60 cm between rows, so there’s room for small companions in between. The plant spacing calculator shows how many tomatoes fit in your bed.

1. Plant the tomatoes first, at full spacing.
2. Put basil, parsley or a French marigold in the gap between each pair of plants, at least 20 cm from the stems.
3. Edge the bed with chives or a short row of carrots on the sunny side.
4. Keep taller flowers such as cosmos to the north side, so they don’t shade the tomatoes.

In a greenhouse, French marigolds and basil in the border or in pots by the door are about all the room allows.

What to expect from companion planting

Some pairings have reasonable support behind them, mainly flowers that bring in hoverflies and other insects that eat aphids. Others are tradition that has never been properly tested. The clashes are worth taking seriously, because most come from a shared disease or pest, as with potatoes and blight.

So use companions for what they’re good at: filling space, drawing in helpful insects and keeping a bed varied. Don’t rely on them in place of netting, good spacing and moving tomatoes to fresh ground each year. Our companion planting guide goes through the pairings with the best reasons behind them.

For timings, see when to sow tomato seeds.