The best neighbours for tomatoes are usually plants that stay relatively low, do not steal too much light and leave air moving between tomato leaves. Basil, lettuce, radishes, some onions and ornamental flowers can fit well. Avoid crowding tomatoes with large, competing plants, and treat other nightshades with care because they share some pests and diseases.
What grows well beside tomatoes?
Think first about how much room the plant will occupy in June and July, not how small it looks when planted. A low crop that finishes early can make good use of bare soil while tomatoes are getting established. Keep enough space for watering, tying in plants, harvesting and removing damaged leaves.
Basil, marigolds and low-growing vegetables
Basil enjoys the warmth associated with tomato growing and can be placed nearby without taking up much vertical space. It still needs light and water. Do not assume that basil automatically prevents tomato diseases or eliminates insects. Its main benefit in a small plot may simply be efficient use of space.
French marigolds can add flowers and biodiversity around beds. Claims that every marigold repels every pest are exaggerated. Use them as companions, not as a substitute for checking plants. Lettuce, radishes and spring onions are practical short crops where they will not be shaded too heavily. Harvest them before tomato foliage fills the space.
They can, provided they have enough room and the soil suits both crops. Onions and spring onions generally take less space above the ground than tall leafy crops. Carrots use more of the root zone, but they still compete for moisture and nutrients. Garlic has a different growing calendar, so consider when the bed needs to be cleared or prepared.
Why potatoes are a poor choice nearby
Potatoes and tomatoes both belong to the nightshade family and can suffer from late blight and some other problems. Growing them close together can make it harder to manage disease in a damp season. The risk is not a mysterious chemical dislike; it comes from shared pathogens, dense foliage and cultivation needs.
Peppers, aubergines and cucumbers: possible with care
Peppers and aubergines may grow near tomatoes, but they have overlapping disease and pest risks. Give each crop enough light and maintain hygiene when symptoms appear. In a polytunnel, cucumbers and tomatoes also need to be planned carefully. Cucumbers often prefer more humid growing conditions, while permanently damp tomato foliage can increase disease risk. Good ventilation and separate watering zones are more useful than a rigid ban.
What about cabbages and broccoli?
Large brassicas can occupy a great deal of space and compete with tomatoes. That is usually the practical difficulty. There is no need to claim that cabbage poisons tomatoes merely by growing nearby. On a large plot you can accommodate both; in a narrow bed, choose smaller companions that do not block access or airflow.
Spacing matters more than a companion-planting chart
A crowded bed shades leaves, slows drying after rain or watering and complicates inspection for pests. Leave room for mature tomato plants before filling gaps with herbs or flowers. If tomato leaves begin to curl or change shape, check soil moisture and the newest growth rather than blaming a neighbouring species without evidence. Our guide to curled tomato leaves explains the main causes.