Planning your garden or allotment to include certain plants side-by-side offers many natural benefits. This is known as companion planting and can help keep pests at bay, attract helpful pollinators and may even improve the flavour of your veg at harvest time. In this guide, we offer our expert tips on what to plant with onions as well as the advantages of crop rotation.
The Best Onion Companion Plants
There is a vast range of onion companion plants that are worthwhile in planning for your growing space. This can provide benefits for various other plants in your growing space due to their proximity to onions. Additionally, many plants can benefit onions when planted near onion sets. You can find out about both in our lists of what to plant with onions below.
Plants That Benefit From Onions
Onions can be an effective companion plant for other crops because their strong smell helps to deter pests like aphids, as well as larger visitors to your patch like rabbits.
Plants that benefit from being planted close to onions include:
- Brassicas - Onions help to deter cabbage worms, loopers, and maggots when planted near brassica plants like broccoli, kale, cauliflower, turnips, Brussels sprouts, and traditional cabbage.
- Carrots - Onions have a repellent effect on carrot fly which can affect carrot seeds after growth.
- Beetroot - As a natural deterrent of aphids, sugar beet-flea beetles, rabbits and deer, onions can help protect your beetroot plants .
- Strawberries - A notoriously vulnerable crop, strawberry plants can fare better when planted near onions, which repel aphids.
- Tomatoes - Another favourite of many insect pests, tomato plants can be protected by nearby onions.
Plants That Benefit Onion Growth
It’s also the case that other crops can benefit onions if planted in close proximity, bringing advantages in growing conditions, flavour and pest-repelling ability. These onion companion plants include:
- Chamomile - As well as being good to grow for a cup of tea, this herb plant can help to improve the flavour of onions when grown nearby.
- Summer savory - Sowing some of these classic herb seeds helps to sweeten your onions and also encourage their growth.
- Leeks - Despite being a part of the same family, leek plants are great at confusing onion flies, helping to protect your crop. They also have similar growing condition requirements.
- Swiss chard - With large leaves, chard plants can provide shade over the surrounding soil, helping to keep it moist and beneficial for your onions. Planting onions with swiss chard also helps to protect your chard from pests.
You should also consider other plant combinations that aren’t directly beneficial to each other but can be helpful in other ways. For instance, lettuce plants 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.
What Not to Plant with Onions
Although there is a wide range of onion companion plants that work excellently, as mentioned above, there are several plants that you should avoid planting alongside them. Certain plants may inhibit your onions’ growth, or vice versa, so you should plant the following plants away from your onions:
Potatoes
Both require different growing conditions, as onions require neutral or slightly alkaline soil, while seed potatoes prefer slightly acidic soil. They can also compete for nutrients, as both are heavy feeders. They also attract different pests, which could cause pest problems to increase. However, planting potatoes after onions for crop rotation can work if the soil’s pH is lowered with organic matter such as pine needles, leaf mould or sulphur.
Beans and Peas
Growing onions near bean plants and pea plants can affect their growth, so they shouldn’t be planted together. Onions secrete certain substances, such as sulphur-based compounds, that can interfere with the beneficial bacteria that beans and peas need to grow well.
Asparagus
Asparagus seeds can be affected by being grown near onions as they both compete for the same nutrients.
Sage
Sage and onion plants prefer different growing conditions, so they will need to be grown away from each other. Sage prefers drier conditions and well-drained soil, while onions should be grown in moist, fertile soil.
Can You Plant Onions in the Same Place Every Year?
When plants from the same family are planted in the same spot year after year, the soil can become deprived of vital nutrients. This affects the quality and yield of harvested crops in the long run.
The risk of plant-specific, soil-borne diseases can also increase when onions are planted in the same spot every year. For this reason, it’s recommended not to plant onions, shallots or garlic in the same bed every season. And this 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.
The Benefits of Onion Crop Rotation
To combat these problems, it is best to practise onion crop rotation. This process involves rotating different families of plants in order to balance out the soil deprivation. This way, when you add new nutrients using garden compost or garden fertiliser, you bring the soil back up to a higher, more balanced level instead of making the soil too rich in certain nutrients.
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, you can set up three beds and create a cycle where each crop moves to the next bed for the following year.
Frequently Asked Questions on Onion Companion Planting
What Pests Do Onions Naturally Repel?
The scent of onion plants deters a wide variety of pests, which include carrot flies, cabbage worms, loopers, aphids, and even rabbits and deer.
Can You Use the Same Companion Plants for Both Spring Onion and Onion Plants?
Companion plants for spring onions and onions are the same. They are both from the allium family, deter the same pests due to their scents and will do well when grown near the beneficial plants listed above.
How Far Should I Plant My Companion Plants From My Onions?
The distance you should leave between your companion plants and your onion plants will differ depending on the type of plant you’re growing.
A large number of plants can be spaced 10-15cm (4-6 in) apart; however, bigger plants will need more space. Incompatible plants, such as beans and potatoes, should be planted 60-90cm (2-3 ft) away from your onions, or ideally in another section of your growing space.
Shop Quality Onion Sets at D.T. Brown
To grow healthy onions that are full of flavour, you can find many onion sets in a range of cultivars at D.T. Brown. These are disease- and virus-free and chosen for their quality, so you can grow with confidence. With over 100 years of experience providing gardeners with exceptional vegetable plants and vegetable seeds, you can rely on our bulbs to grow vigorously in your garden.
For further advice on onion cultivation, you can find our guides on how to grow onion sets and how to grow onions from seed, which include guidance on each stage of growth.
If you’d like to know more about our range of fruit plants, flower plants, or anything else from our extensive range of gardening supplies, contact us today and a member of our team will be happy to help you.
