What to plant with onions

Planning out your garden or allotment beds is a good way to take advantage of the natural benefits of planting certain varieties or types of plants near one another. This is known as companion planting and can help to thwart pests, attract helpful pollinators and may even improve the flavour of your veg come harvest time.

What grows well with onions?

Onions can be very effective as a companion plant to other crops because the strong smell helps to deter pests. The smell of onions can protect against insect pests such as aphids as well as larger visitors to your patch like rabbits. 

Plants that can be helped along by proximity to onions include:

• Brassicas - Onions help to deter cabbage worms, loopers and maggots. Options include broccoli, kale, cauliflower, turnips and brussel sprouts, as well as traditional cabbage.
• Carrots - Onions have a repellent effect on carrot fly.
• Beetroot - As a natural deterrent of aphids, sugar beet-flea beetles, rabbits and deer, onions can help to keep your beetroots protected.

Strawberries - A notoriously vulnerable crop, strawberries can fare better when planted near onions to repel aphids.

Tomatoes - Another favourite of many insect pests, tomato plants can be protected by nearby onions.

It’s also the case that other crops can have benefits for onions if planted in close proximity, bringing advantages in growing conditions, flavour and pest repelling ability. These include:

Chamomile - As well as being good to grow for a cup of tea, chamomile can help to improve the flavour of onions when grown close by.

Summer savory - This classic herb helps to sweeten your onions and encourage their growth.

Leeks - Despite being a part of the same family, leeks are great at confusing onion flies, helping to protect your crop. They also have similar requirements in terms of growing conditions.

Swiss chard - With large leaves, swiss chard can provide shade over the surrounding soil, helping to keep it moist. This encourages beneficial growing conditions for your onions. Planting onions with swiss chard makes for a mutually beneficial relationship as onions help to protect the swiss chard from pests.

You should also consider other plant combinations which aren’t directly beneficial to each other but can be helpful in other ways. For instance, lettuce provides few benefits to onions and vice versa, except that the two plants have differing root depths. This means that lettuce won’t compete with your onions for nutrients, so they can be planted closer together in order to maximise your use of space in the garden.

Can you plant onions in the same place every year?

When plants of the same family are planted in the same spot year after year, the soil can become deprived of the nutrients that family uses the most. This can then affect the quality and quantity of harvested crops in the long run. To combat this, crop rotation involves rotating different families of plants in order to balance out the soil deprivation. This way, when you add new nutrients using compost or fertiliser, for instance, you bring it back up to a higher, more balanced level rather than making the soil too rich in certain nutrients.

Plant-specific, soil borne diseases can also increase, for this reason, it’s recommended not to plant onions, shallots or garlic in the same bed every year. It also helps to reduce the build up of pests that attack the onion family, as their numbers will decline during times when onion plants aren’t present. 

A sample rotation could look like this:

Year one: Onions

Year two: Brassicas

Year three: Potatoes

Instead of missing out on onions for a couple of years while your other crops are growing, set up three beds and create a cycle where each crop moves to the next bed for the following year.