10 plants that should never be grown together

Living Well | Words: Sue Hewitt | Images: Getty | Posted on 02 November 2020

Some plants are mortal enemies. Here are 10 you should never grow together.

There are good neighbours and bad in every ’hood – the ones who help you and those who make things difficult. It’s the same in the plant world.

There are plants that ‘fight’ with one another, sucking up all the nutrients from the soil and leaching substances harmful to other plants or spreading diseases. Others are thirsty beasts that will guzzle vital moisture and leave their bed-mates parched.

It’s not that you shouldn’t include these plants in your vegie patch, you just need to make sure you plant them next to the right neighbours. Like people, some plants simply don’t get along.

Julia Reynolds, a horticulture teacher at Melbourne’s Holmesglen Institute, says many gardeners know about companion planting, such as planting basil or onions and garlic near your tomatoes to help deter insect pests. 

But on the other hand, planting tomatoes near cabbages or cauliflowers is asking for trouble because brassicas are gluttons and will out-feed the tomatoes, she says.

So, if your vegies have been performing badly, perhaps it’s because they don’t get on with their neighbours. 

We asked Julia to reveal the bad-neighbour combinations for 10 popular plants in Victorian vegie patches.

Row of name labels for a garden

If there’s trouble in the vegie patch, it could be the neighbours.


10 plants that should never be grown together


Beans

Avoid planting your beans near garlic, onions or leeks as these exude a substance that can kill beneficial bacteria that help legumes, such as beans, to convert nitrogen from the soil into food.

Cabbage and cauliflower

Avoid planting near eggplants which, along with other members of the solanaceae family including potatoes and tomatoes, prefer acidic soil, while brassicas prefer more alkaline conditions. You won’t get the pH balance right for both. 

Carrots

Avoid planting near coriander which can excrete a substance from its roots that stunts carrots. If you can only grow stumpy carrots, coriander planted nearby could be the culprit. 

Cucumbers

Avoid planting near potatoes, cabbage and cauliflower which love water even more than cucumbers and will out-compete them for any moisture.

Lettuce

If you’re planting from seed, avoid sowing near cabbages and cauliflower which leach a substance that stops the lettuce seed from germinating.

Tomato plant
Potatoes in the dirt
A carrot being picked from the garden

When it comes to gardening, some plants are mortal enemies.


Peas

Avoid planting peas with onions, leeks or garlic. They will kill the beneficial bacteria that peas need to convert nitrogen from the soil into energy.

Potatoes

Potatoes should be planted on their own as they out-compete other root vegies and also have the same pests as tomatoes.

Sweet corn

Avoid planting with cabbage or cauliflowers which are heavy feeders and will out-compete the corn for nutrients. And don’t plant corn near celery as both love a drink and will compete for this vital resource.

Strawberries

Avoid planting your strawberries near tomatoes, eggplants or anything else from the solanaceae family. These are susceptible to verticillium wilt, a fungal disease that may kill the strawberries.

Watermelon

Keep away from zucchini and squash as they attract pests which attack watermelon. They will also out-compete the watermelon for water.