5 plants you should never grow with tomatoes – experts warn they can cause poor-quality fruits and disease

Calling all tomato lovers: Did you know there’s a whole list of plants not to grow with tomatoes?

That’s right; there’s so much more to learning how to grow tomatoes than popping them in the best soil and pruning them like a pro. Why? Because these grow-your-own favourites need to make nice with their neighbouring plants if you’re really hoping for them to thrive.

Of course, the basics of companion planting should help you suss out which plants will help your tomatoes to some degree. That being said, it’s just as important to figure out the crops to avoid planting alongside these Mediterranean lovelies.

Here’s what the experts have to say on the matter…

'We spend a lot of time thinking about the best plants to grow alongside tomatoes – either because they enhance the soil, repel pests, or enhance that all-important tomatoey flavour,' says Christopher O’Donoghue, one of the directors of Gardens Revived.

'Every good gardener worth their salt, though, will tell you that there are plenty of plants not to grow with tomatoes, too – usually because they do the opposite of everything on that list above!'

Christopher O'Donoghue

A gardener with over a decade of experience under his belt, Christopher set up Gardens Revived with his brother, Andrew, in 2018 to create a thriving family business. Together, they have worked on residential gardens, listed buildings and gardens, flower shows and large estates with some exceeding 70 acres – many with historical significance.

With that in mind, then…

1. Brassicas

As a general rule of thumb, it’s a good idea to plant crops alongside one another if they work well together in a meal. And that’s why Morris Hankinson of Hopes Grove Nurseries advises you to steer clear of 'brassicas, such as kale, cabbage, cauliflower and sprouts.'

Morris Hankinson

Morris Hankinson is the founder and managing director of Hopes Grove Nurseries Ltd, the UK’s only specialist grower-retailer of hedging plants. He established the thriving business in 1992, shortly after graduating with a Commercial Horticulture Degree from Writtle College, Essex.

'These are heavy feeders which can compete with tomatoes for nutrients, water and space,' he explains.

'They should be planted separately in the garden so they both have plenty of their own space to grow.'

2. Sweetcorn

You may have learned how to grow sweetcorn like a pro, but be sure to do it away from your toms – corn is one of the plants not to grow with tomatoes, according to experts.

'Sweetcorn grows taller than tomatoes and will easily shade tomato plants, limiting their growth,' says Morris.

'Together they will compete for sunlight, nutrients and space. As such, these are two crops to plant well away from each other.'

3. Potatoes

You say tomato, we say potato – because these tasty veg (fine, veg and fruit!) should never be planted alongside one another if you want to avoid blight.

'Potatoes and tomatoes are both susceptible to blight which can devastate crops by spreading very quickly,' says Morris.

'If these are planted together, it could increase the blight to spread and both will be affected. Keeping them separated means at least one of the two might be safe if blight does creep in.'

For those keen to grow something like the potato 'British Queen' from Crocus, then, make sure you have to space to do it well away from your toms.

4. Fennel

Delicious when served with purple sprouting broccoli and chilli flakes, fennel is another of those plants not to grow with tomatoes.

'Fennel inhibits tomato growth, along with some other plants, due to allelopathy,' says Morris.

'This is when the plant releases toxic substances from the roots which inhibit the tomato plant from absorbing nutrients necessary to thrive.'

5. Carrots

Perhaps a surprising addition to our list of plants not to grow with tomatoes is the humble carrot – for good reason.

'Carrots and low-growing crops will likely be shaded by the foliage of tomato plants if planted next to each other, which will impact the growth rate of the carrots or crops,' says Morris.

'These are best planted away from each other for the benefit of each.'

FAQs

What should you never plant next to tomatoes?

Potatoes, brassicas, and fennel should never be planted next to tomatoes, as they can hinder growth, compete for nutrients, and even make your crops more susceptible to disease.

'Potatoes are prone to the same blight diseases as tomatoes, increasing the risk of infection,' says Christopher O’Donoghue of Gardens Revived.

'Cabbage, broccoli, cauliflower, brussels sprouts, and kale, meanwhile, will compete heavily for nutrients and can stunt tomato growth – much like fennel.'

What is the best companion plant for tomatoes?

If you’re looking for the best companion plant for tomatoes, you should consider sowing basil, chives, marigolds, or onions.

'All of these are excellent pest deterrents,' says Christopher O’Donoghue of Gardens Revived.

'Better still, you’ll find that planting your tomatoes next to something like basil, chives, or onions will actually enhance their flavour come harvest time!'

And just like that, you know the plants not to grow with tomatoes. Take care to heed our advice when it comes to sowing your seeds this spring, and you’ll be in for a brilliant harvest later in the summer…