Companion planting – which essentially means planting onions with other crops, herbs or flowers 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. Onion companion planting is an important element in how to grow onions, and while you might think it sounds complicated, it 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, so you enjoy better results from your vegetable garden ideas.   This easy guide should help you to decide what plants to grow alongside your onions in order to ensure a super delicious bumper harvest. 

Onion companion planting

Onions are one of the easiest vegetables to grow and produce large yields making them a favorite of the veg patch, especially for small vegetable garden ideas where every bit of space needs to be as productive as possible. With onion companion planting, you can boost the crops even more. Onions also offer a host of benefits to other plants, too, making them the ideal contender for those starting out with companion planting.  ‘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 (opens in new tab). This is great for those interested in permaculture gardening and to create a sustainable garden full of happy, healthy plants and crops.

What can I plant with onions?

There is a wide range of plants that can be grown with onions, including other vegetables, herbs, and even flowers. Through onion companion planting, each plant will benefit. Regardless of whether you are growing your onions from seed or sets, when you plant onions you should also think about companion plants. This is an important aspect of planning a kitchen garden

Onion companion planting – with vegetables

There is a wide range of vegetable crops that are perfect partners for onion companion planting. If you practice onion companion planting alongside crop rotation you will increase your chances of a healthy harvest. CARROTS  Planting onions, specifically growing spring onions, with carrots is a classic combination that many gardeners swear by. The smell of onions deters carrot root fly from the carrots for carrot companion planting, 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 (opens in new tab). CABBAGE  Onions get on well will all members of the cabbage family (brassicas), which also includes 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.  TOMATOES  Due to their strong scent, onions also deter aphids and Japanese beetles from running amuck over your tomato plants, so are ideal for tomato companion planting, and tomatoes will not compete with onions for soil nutrients.  PEPPER  Plant onions around the base of your peppers to deter aphids and Japanese beetles.

Onion companion planting – with herbs

As part of your herb garden ideas, plant herbs among your crops for onion companion planting. PARSLEY & MINT  Growing mint or parsley as onion companion planting helps to ward off onion fly. The fragrant leaves of both mint and parsley help confuse the onion fly, which likes 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 time to harvest onions.  However, ’take care with some companion plants such as mint,’ cautions Sue Sanderson, horticultural executive at Thompson & Morgan (opens in new tab). ‘These are fast-growing plants and will quickly smother your crop. Ideally grow mint in a herb planter alongside the crops to keep it under control.’ CHAMOMILE  This pretty daisy-like flower and aromatic herb has plenty of benefits for the garden. It is a good plant for pollinators, attracting pollinators with its 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 used as an onion companion plant it also improves the flavor of the onions.  SUMMER SAVORY  If you prefer your onions to taste sweeter, onion companion planting with summer savory is the perfect combination. It will also help to encourage the growth of your onions. 

Onion companion planting – with flowers

There are many blooms that as well as being beautiful and fragrant flowers, are also, surprisingly, excellent for onion companion planting. ROSES  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 as flower bed ideas. Planting alliums or chives as part of your rose garden ideas will help to deter aphids and black-fly, keeping your rose blooms looking beautiful.  CHRYSANTHEMUM  One of the most popular late summer flowers and flower for the fall garden, pair chrysanthemums with chives ‘as the onion scent will deter aphids,’ advises Sue Sanderson of 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 vegetables should not be planted with onions?

There are various vegetables that you should not plant with onions. You should not  grow peas, beans or asparagus next to onions as they require different conditions and therefore in order for one to thrive, the other will not.  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.

Can I plant onions next to tomatoes? 

You can plant onions next to tomatoes. As mentioned about, in fact, growing tomatoes next to your onion crop may help to deter pests from bothering your tomato crop. ‘These pungent vegetables make great tomato companion plants. Their unappealing odor is a natural deterrent of many garden pests that feed on tomato plants, explains Bob Lawson from Kellogg Garden (opens in new tab).

 Can I plant onions next to cucumbers? 

As onions are classed as root vegetables, meaning they grow beneath the soil, and cucumbers are not, they do make good for cucumber companion planting. If you are growing cucumbers, they send one long root down, taking nutrients and water from deeper in the soil. For this reason, the plants do not compete with one another for nutrients. 

Can I plant onions and peppers together? 

You can plant onions and peppers together. As onions do not take up a lot of room above the ground, they are good to plan as neighbors if you’re growing peppers.  Also, onions have a strong smell with helps to deter a lot of pests such as aphids and slugs, making them great for pepper companion planting.