Onion Companion Plants: Allium Allies

Companion planting is an old but popular strategy. Gardeners and farmers have been employing this organic gardening technique for years, and it’s undergoing a revival of sorts in backyard gardening. As people try to abandon artificial fertilizer and pesticides to hone in on more natural practices, growing companion plants has become more important. For those stocking their home pantry, choosing the right onion companion plants is essential to get maximum yields. 

Your goals with companion planting should be carefully considered. A companion planting like beans and strawberries works well because the beans feed nitrogen to the strawberries, and the strawberries cover the soil and keep it moist for the beans. Likewise, with onion companion planting, the benefits only work when it’s done correctly. 

While planting onions and other alliums like garlic from seed can be quite difficult, it’s much easier to grow from ‘onion sets’. This term refers to a baby onion bulb that will grow and develop into a full-sized onion. This quick-growing plant is almost a sure bet and is useful to have on hand when companion planting with other crops. Also, consider planting onions that have already sprouted.

There are all sorts of reasons to companion plant. Some pairings of plants result in better tasting food. Others result in fewer pests. Some companion plants provide shade or structure to one another like corn and beans, while others can shade the ground and retain water like the large leaves of the squash plant.

When companion planting with onions in your garden, determine what problems you might have that the onions could help with. Did you want sweeter crops? Fewer buggy crops? Did you want to get a larger harvest out of your row of carrots or lettuce? See where onions can really help to improve your garden and plan accordingly! 

What Is Companion Planting?

Companion planting is a system where different crops are planted either among one another (think a carrot in between every onion plant) or in neighboring rows or beds. By doing companion planting, each plant can help another in some way by growing nearby. This help can come in the form of improved flavor, pest protection, nutrient sharing, structure, weed abatement, shading, or water retention. 

How does companion planting work? There are several different ways. Let’s use peas and beets as an example. The roots of the pea plant develop nodules that will fix nitrogen in the soil around its roots. This nitrogen is then fed on by the beets and helps them to grow larger and healthier. This type of companion planting is called nutrient sharing. 

One of the most famous examples of good companion plants is the ‘Three Sisters’ grown by Native Americans. These are corn, beans, and squash. The corn stalks grow tall and provide support for bean vines to grow on. The beans add nitrogen and fertilize the soil while the squash leaves shelter the soil and retain water and prevent weeds. This symbiotic relationship results in a much healthier harvest. 

Some plants, like yarrow, attract beneficial insects. Not only do butterflies and bees like this colorful plant, but lacewings are attracted by the cloudlike formations of yarrow flowers. Lacewings eat aphids – one of the most common pests in the garden that not only eat and damage crops but spread disease. This type of companion planting reduces pests. 

Radishes are great near onions, especially onion sets that have not yet poked out of the ground. Radishes are quick to germinate and will mark where the row of not yet visible onions are growing. This way, you can companion plant to mark your garden rows. 

As you’ll see with growing onions, the scent of many of the members of the onion family can repel garden pests such as Japanese beetles, the carrot fly, and cabbage worms. By choosing to plant certain plants with others, you can prevent crop damage before it starts. 

A method to trap pests that are always present in the garden (like aphids) is to plant nasturtium. The nasturtium is used as a sacrifice or trap crop. It lures the aphids to it, and once it’s infested, it’s picked from the garden and disposed of. It doesn’t hurt that the flowers of the nasturtium are quite beautiful as well! 

Good Onion Companion Plants

Onions are a great companion plant to members of the brassica family (commonly known as the cabbage family), and not just because you’ll find them in the same dishes! The pungent smell of the onion help repel pests that naturally prey on cabbage, broccoli, kale, or cauliflower, namely the cabbage worm, cabbage loopers, and cabbage maggots. Members of the cabbage family such as kale, broccoli, brussels sprouts, and napa cabbages do well when planted near these pungent bulbs in the garden. 

For gardeners battling aphids, the entire onion family makes good companion plants to have near tomatoes, lettuce, strawberries, and peppers like bell peppers or jalapenos. You’ll find that growing onions near tomato plants can even better the flavor of the tomatoes. For lettuce or strawberries, the scent of the onions planted alongside them will repel a few other sap-sucking pests too.

Onions can also deter spider mites, meaning that companion planting tomatoes, peppers, and onions together is a huge boon for these delicious crops. Spider mites can cause serious damage and stunt foliage growth on those plants, so having companions nearby that slow them down is a good choice. Putting a mix of onions, peppers, tomatoes, and marigolds together will seriously reduce pest issues on your peppers and tomatoes!

Onions may be a root crop, but onions draw from different levels of nutrients in the soil than carrots or parsnips. When intercropped with carrots, spinach, and lettuce they actually don’t compete for nutrients. They grow well together because they feed at different levels of the soil. The carrot sends its taproot deep into the soil to feed, while the onion bulb draws from the top few inches of soil. Lettuce and spinach are even more shallow-rooted than the onions. You can get a stair-stepped series of root growth in the soil using this method.

While intensive, this type of gardening will yield a large vegetable crop! The smell of the onion will also repel the carrot fly, a common pest of carrots. The aroma also wards off many other pest types such as aphids and flea beetles. This symbiotic relationship between lettuce, carrots, and onions makes it one of the most popular crop pairings.

Use root crops such as radishes to pop up quickly to mark rows where your slow-growing onions are. The radishes will be ready at about the time that the onions are visible, and you won’t accidentally overplant.

Many herbs that are planted alongside onions may actually improve the flavor of the onions. Herbs such as summer or winter savory, marjoram, rosemary, and dill will better the flavor of onions. Mint and parsley also improve the flavor of your onions, while summer savory makes them sweeter! Just be careful, and consider adding onions to your bed of herbs instead of the other way round. Mint can take over your gardening box, and quick-to-flower dill and parsley plants can drop seeds that return annually.

Another set of companion plants to grow together in the garden is chamomile and onions. The antifungal nature of chamomile helps to prevent some fungal issues on onions, a problem in more humid climates. The chamomile plants also attract beneficial insects to the garden that can eat bugs like aphids. 

An option for the home orchard ravaged by Japanese beetles or aphids would be to place containers in the orchard and companion planting onions, carrots, and summer flowers or herbs such as marigolds, dill, summer savory, and parsley. Not only will you get additional vegetables but the companions work together to improve the health of your garden. The onions reduce pests, while the flowers attract beneficial insects that can pollinate your orchard buds.

What Not To Plant With Onions

There are a few plants that you should avoid planting with your onion plants. Different plants interact with one another differently and are not all good companions. 

One summer vegetable you should never plant near onions is asparagus. As asparagus is a perennial and takes years to get established, it’s best to put the two plants in completely separate areas of the vegetable garden. Companion planting onions with asparagus creates competition for soil nutrients.

Other vegetables that don’t do well around onions are beans, peas, and most other crops in the legume family. The presence of the allium family plants can harm beans and peas as they can stunt their growth. There is a chemical incompatibility that keeps peas, fava beans, pole beans, bush beans, lentils, or other legumes from having a stable and beneficial relationship. Avoid garlic, onions, leeks, and other alliums in the same bed as these crops.

Like with most plant families, members of the allium family are often plagued by the same diseases and pests. Because of this, it’s beneficial to keep other members of the allium family (think leeks, garlic, chives, shallots, garlic chives, and other onions) away from one another. If you plant these vegetables together, they’re likely to attract many of the same pests, namely onion maggots and onion flies. Both of these pests can seriously harm your plants and stunt the growth of your future onions. 

Another garden vegetable companion planting to steer clear from is sage. While sage is known to stimulate growth for a wide variety of vegetables, onions are not one of them. Keep your onion crop far away from sage as it can actually stunt the growth of your plants! 

Additionally, companion planting turnips with onions results in the loss of flavor, only this time in the turnips. 

Frequently Asked Questions

Q: Can I plant onions with cucumbers?

A: Not only will the smell of the onions repel pests that prey on cucumbers, but the roots of the onion plants grow in a different soil layer from the deep taproot of the cucumber. 

Q: Can onions be planted with tomatoes?

A: Yes, they’re one of the best plants to grow alongside your tomatoes. The smell of the onion plant and other alliums can repel insects and beetles that prey on tomatoes when you plant onions near tomatoes.