By Holly Reaney
Onion companion planting – in other words, planting onions with plants that will be beneficial to their healthy growth – can help you to get the most out of your garden by deterring pests and increasing your harvests.
See: Companion planting – an ultimate guide
'With some careful planning and by gardening smart you can grow a community of mutually beneficial plants so your crops will thrive without needing intervention and avoids the use of harmful pesticides' says horticultural expert Rob Smith from the Organic Gardening Catalogue.
While it may sound complicated, onion companion planting is actually very easy. You simply plant two or more different plants next to them that are known to be mutually beneficial, whether that's in terms of harvest, improving flavor and quality, or deterring pests.
Onions are one of the easiest plants to grow and produce large yields making them a favorite of the veg patch. However, they also offer a host of benefits to other plants too, making them the ideal contender for those starting out with companion planting.
With a wide range of varieties to choose from, it's easy to find the perfect pick for your space. So, whether you choose red onions, sweet white onions or scallions, we have rounded up the best plants to pair when companion planting onions.
What can I plant with onions?
There is a wide range of plants that can be grown with onions, including other vegetables, such as carrots, herbs, such as parsley and mint, and even flowers, such as roses. In doing so, each plant will benefit.
Onions can be grown from seed which is the most cost-effective method and great for smaller scallion varieties. However, for larger types it is much quicker and easier to grow them from sets (which are just small onions) - these can be bought at most garden centers.
Regardless of whether you are growing your onions from seed or sets, you will start planting them outside in spring. At this time, you should also consider which plants you will be companion planting your onions with – read on to find the perfect pairings as well as those to avoid.
See: Kitchen garden ideas - 10 easy ways to get started
Onion companion planting – with vegetables
Planting onions, specifically spring onions, with carrots is a classic combination that many gardeners swear by. The smell of onions deters carrot root fly from the carrots while the smell of the carrots helps to deter onion fly from the onions – a highly beneficial pairing.
However, there have been mixed reports of the success of this method, with some gardeners convinced, while others are less sure.
'If you are particularly worried about carrot fly you can 'use Enviromesh or fleece around the edges of the carrot bed, stretched as a screen three-feet high. The pest is a ground flyer and won’t make it over the screen,' advises gardening expert Sarah Raven.
Onions get on well will all members of the cabbage family (brassicas) which also include lettuce and broccoli. This is because companion planting with onions provides good resistance to cabbage worm, weevils and cabbage looper. The aroma of the onions also helps to confuse rabbits seeking out the scent of leafy greens to enjoy.
Due to their strong scent, onions also deter aphids and Japanese beetles from running amuck over your tomato plants. You can read more about tomato companion planting in our dedicated guide.
Plant onions around the base of your peppers to deter aphids and Japanese beetles.
- See: How to grow potatoes – a step-by-step guide
Onion companion planting – with herbs
PARSLEY & MINT
Companion planting onions with parsley or mint helps to ward off onion fly. The fragrant leaves of both mint and parsley help confuse the onion fly who like to breed in the onions leaves. Onion fly maggots will also eat their way through the onion bulbs leaving you with no crop come the harvest.
'Take care with some companion plants such as mint,' says Sue Sanderson, Horticultural Executive at Thompson & Morgan in a recent blog post. 'These are fast-growing plants and will quickly smother your crop. Grow mint in containers to keep it under control.'
This pretty daisy-like flower has plenty of benefits to the garden, attracting pollinators with their sweet fragrance as well as being able to be dried to make a calming tea. It is also antibacterial and anti-fungal, helping to protect your plants. As if this isn't enough when chamomile is companion planted with onions also improves the flavor of the onions.
If you prefer your onions to taste sweeter, companion planting onions with summer savory is the perfect combination. It will also help to encourage the growth of your onions.
Onion companion planting – with flowers
Alliums and chives are also both members of the onion family and have the same benefits of companion planting as the traditional vegetable while also looking beautiful in the border. Planting alliums or chives in your rose bed will help to deter aphids and black-fly, keeping your blooms looking beautiful.
See our guide to how to plant roses to ensure your blooms are plentiful this summer.
One of the most popular fall garden flowers, pair chrysanthemums with chives 'as the onion scent will deter aphids' advises Sue Sanderson, Horticultural Executive at Thompson & Morgan.
If you're short of room, species of onions including scallions and chives are a very compact choice for companion planting. 'Where space is limited, add in crops among your flowers, selecting beneficial partners, such as fringes of chives, to attract garden helpers to the vegetables,' advises gardening expert Leigh Clapp.
What should not be planted next to onions?
You should NOT plant beans, peas, sage or asparagus next to onions as they require different conditions and therefore in order for one to thrive, the other will not.
- See: How to grow garlic – a step by step guide to growing from cloves
Surprisingly other onion or allium plants (such as garlic, shallots or leeks) also make a poor companion plant for other onions as they are all vulnerable to onion maggots. These will travel from plant to plant and can quickly decimate a bed. Plant these plants far apart to prevent any spread – that way even if one area of onions fall victim, you still have others to fall back on.
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