8 Best Companion Plants For Onions And 3 To Avoid

Onions are a low-maintenance, easy-to-grow crop that is a common sight in gardens across the nation. With varieties of different shapes, colors, and tastes – onions also can be grown from seed or by way of ‘onion sets’ (small pre-grown onion bulbs).

Although simple to grow, the chances of a successful yield can be improved dramatically by using the gardening technique known as companion planting.

Onions make great companion plants for many other plants, however, I want to share a few onion companion plants that also help onions to grow. 

Onions are a great crop for your garden and with the straightforward and effective approach of companion planting you can boost the health and vigor of this year’s onion harvest.

Key Takeaways

  1. Companion planting is a valuable technique for improving the health and yield of onions. By growing compatible plants nearby, you can deter pests, save space, and enhance soil health.
  2. Choose the right companion plants for onion growth. Good options to grow alongside your onions include lettuce, carrots, radishes, tomatoes, beets, chamomile, rue, and summer savory. These plants provide benefits such as pest deterrence, space utilization, and flavor enhancement.
  3. Avoid planting incompatible companions like asparagus, fennel, alliums, leeks, or garlic plants next to onions. These plants can compete for resources, inhibit growth, or attract pests that can damage onions.

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What Is Companion Planting

companion plants for onions

Companion planting is a popular method of gardening that involves growing one or more species of plant in close proximity with the aim of benefiting one or both crops. 

Let’s face it, every grower strives for a happy, healthy, and balanced growing environment and one that results in the maximum yield possible. Companion planting has been used for centuries and does exactly that.

When executed successfully this method of growing encourages healthy plants to thrive and produce more crops. 

Companion planting allows the gardener to intercrop lots of different plants which makes great use of the growing area by utilizing as much of the garden as possible. Additionally, this approach increases diversity and improves harvest amounts.

Rice growers in Asia have been using companion planting to their advantage for centuries to improve their rice plant harvests.

Gardeners in China make full use of the flooded growing conditions surrounding rice plants by encouraging a tiny aquatic mosquito fern called Azolla to grow as a companion plant. 

These ferns may be small but have the capability to increase their numbers rapidly, creating a weed-suppressing blanket around the rice plants. The Azolla plants act as a water purifier, keeping harmful bacteria at bay.

They also release nitrogen into the water which the rice plants then absorb, encouraging faster and healthier growth.

Benefits Of Companion Planting Techniques

green onion companion planting

Companion planting has a multitude of benefits that allows the grower to take advantage of each individual plant’s attributes in a natural and organic way. The practice of companion planting can not only positively influence growing conditions, but also encourage beneficial insects and pollinators.

Some additional benefits of companion planting are:

Pest Management

Companion plants can help to divert and confuse pests and is a good alternative to using synthetic pesticides. With their strong aroma, herbs and onions can help to mask the scent of main crops, luring unwanted visitors away and keeping pests at bay.

Companions may also be used as sacrificial ‘trap crops’ whereby they attract insects such as aphids to themselves and away from precious food crops.

Efficient Use of Space

Companion planting allows gardeners to grow lots of different plant varieties in even the smallest of spaces. This requires planting quick-to-mature, fast-growing plant varieties between slow-growing plants to use space much more productively. 

A good example of this is to grow salad crops such as lettuce or scallions between other slow-maturing plants like tomatoes or eggplants.

Packing in lots of plants in this way will make better use of otherwise unused growing space which increases harvests. 

Improved Soil Health

The key to having bigger, more successful crops with increased yields is to grow plants in nutrient-rich healthy soil and for most growers, this means regular mulching or fertilizing.

However, it is also possible to improve the health of your soil with a little clever companion planting. 

Plants from the Fabaceae family are a very popular choice amongst gardeners for this purpose. That is because beans, peas, and other legumes are able to absorb nitrogen from the air which they then convert and release into the soil.

This extra nitrogen is used by nearby plants to encourage healthy growth and improve harvest amounts.

Thoughts When Selecting Great Companion Plants

Companion planting is a tried and tested method of gardening, but it is also worth noting that there does always need to be some consideration given to plant choice.

For example – Popular planting partnerships are strawberry plants and the beautiful star-flowered plant borage. This planting combination works well because borage encourages pollinators and improves the flavor of the strawberries. 

However, borage – when fully grown – can be as big as 3ft x 3ft, making them significantly larger than strawberry plants’ very small and low-growing nature.

This size difference can significantly impact the strawberry plants’ development and overall health if overshadowed by a mature borage plant.

In addition to size, another consideration is spacing. Most plants need sufficient air circulation and room to grow both above and below the soil surface.

It’s also worth understanding the moisture and nutrient needs of your pairing plants because any competition will have a direct impact on the health and yield amounts. 

This is especially true when water is scarce during dry spells or in hotter climate zones. This competition can be exacerbated for main crop varieties with shallow roots. This detrimental effect can be avoided by implementing a regular watering and feeding routine. 

5 Best Onion Companion Plants To Grow

onion companion plants

Plants from the onion family (allium cepa) are a very popular companion plant choice thanks to their strong, pest-deterring fragrance. When companion planting with onions it is best to choose those that can deter pests (like onion maggots), help utilize growing space, and/or help to retain moisture in the soil in hotter climate zones or when temperatures rise throughout the day.

Here are my top picks of the best onion companions, all of which can be planted near your onions to improve their health and growth rate:

Fruit And Vegetables

Lettuce: Onions and lettuce make great companions. Growing smaller, quick-maturing lettuce varieties alongside onions can be extremely advantageous for a number of reasons.

The smaller butterhead or loose-leaf varieties of lettuce will mature in around 30 days which means space can be utilized more efficiently, helping to maximize crop yield.

In addition, the lettuce plants will also act as an effective cover crop, locking moisture in the soil and keeping competing weeds to a minimum. 

Carrots: Growing carrots and onions together is a classic pairing partnership. Both plant varieties have a very strong and distinctive fragrance which is a proven method of discouraging pests and brings mutual benefit to both species.

The onion scent helps to divert carrot root flies away, preventing them from laying eggs amongst the carrots, whilst the strong aroma of the carrots is known to discourage onion flies from doing exactly the same activity amongst the onions.

Radishes: As one of the easiest and quickest edibles to grow radishes can be harvested in as little as 21 days. Their speedy growth rate means they can be sown or planted in and around onions, picked, and eaten long before the onion plants have matured.

This makes great use of the space and allows more products to be grown. 

The added advantage to growing this small root crop is its ability to loosen compacted soil. Keeping the soil loose allows onion bulbs to swell easily.

TomatoesGrowing tomatoes and onions together make for a harmonious pairing partnership. Firstly, the strong-smelling onions help to combat pest attacks on vining tomatoes. 

Second, planting tomatoes in and around onions will help use the little space you might have. Onions grow shallow roots which means there is no competition for water or nutrients. 

Beets: Planting beets and onions together is beneficial for both plants. Like other pairings in my list, the strong odor of onions helps to deter unwanted pests. Beets return this favor by helping to protect onions from their own unwanted visitors – thrips.  

3 Herbs And Flowers

Chamomile: Chamomile is a great companion plant choice for lots of different plants in the garden including onions.

Not only is it aesthetically pleasing, its delicate white and yellow flowers are a magnet for pollinators and other beneficial predatory insects which helps keep pest populations in check. 

Chamomile also has antibacterial and antifungal properties and is thought to improve the flavor of onions too.

Rue: With its distinctive, strong scent rue helps to deter onion root fly, the larvae of which can devastate a crop of onions in no time causing leaves to curl and bulbs to rot.

Planting rue will help to mask the strong fragrance the onion emits, much the same way onions do when used as companion plants to other garden edibles. 

Summer Savory: A lovely addition to any growing space Summer Savory works very well as a companion to onions. With its slightly peppery taste and tiny white flowers, this annual herb when grown alongside onions will enhance its flavor, giving the bulbs a sweeter taste.

You may also enjoy reading Best Fertilizer For Onions And Garlic | How & When To Use

Bad Companion Plants For Onions

companion planting onions

Of course, there are some plants that should be avoided when growing onions. Many will either compete for water and nutrients, attract the same crop-destroying pests, or even stunt the growth of onions.

Here is my pick of those that do not make good companion plants for onions.

Asparagus: Onions and asparagus are not great companion plants. This slow-growing plant can take years before it is mature enough to produce harvestable crops.

Asparagus is also a heavy feeder and quick to absorb soil nutrients, leaving nothing in the soil for other crops. Planting Asparagus next to onions can stunt the growth of one or both plants.

Fennel: Fennel plants are allelopathic meaning plants release a toxic compound that inhibits nearby plant development and results in stunted growth. Fennel should be planted/grown a good distance away from onion plants.

Garlic, leeks, or other alliums: Theoretically growing plants from the same family should be a good idea. The growing conditions should be the same, feeding and maintenance can be carried out with ease, and harvest times will be similar.

However, growing lots of different plants together which are susceptible to the same pests and diseases can increase the risk of attacks and infection which will spread through all plants very quickly. 

Final Thoughts

Companion planting offers a practical and natural approach to maximizing the health and productivity of your onion crop.

By planting onions nearby other supporting crops, you can create a harmonious growing environment that keeps pests away, optimizes space, and improves soil health.

When you plant onions next to garden plants such as lettuce, carrots, radishes, tomatoes, beets, chamomile, rue, and summer savory, these plants will help contribute to the overall success of your onion harvest.

However, it’s important to be mindful of incompatible companions like asparagus, fennel, garlic, leeks, or other alliums, as they can hinder the growth and development of your onions.

By incorporating companion planting techniques into your gardening practices, you can enjoy a bountiful and thriving onion harvest while promoting a balanced and sustainable ecosystem in your garden.

FAQs About The Best Companion Plants For Onions

What Should Not Be Planted By Onions?

It is best to avoid planting broccoli, certain plants from the onion plant family, and other onions next to each other.

This is because they attract similar pests and have similar nutrient requirements, which would cause your onions to compete for survival.

What Do Onions Deter In A Garden?

Onions have natural pest-repelling properties that can help keep pests away from your garden. Onion plants work well to repel aphids, carrot rust flies, and flea beetles.

A little-known trick to help repel pests is to put a few onion peels in your garden to help ward off pests.

Can You Grow Onions With Tomatoes?

Yes, you can plant onions near tomatoes. These two plants will help keep unwanted pests away, control diseases, and improve nearby soil.

What are the best companion plants for onions?

Some of the best companion plants for onions include carrots, chamomile, and beets. Other great companion plants for onions include pepper plants and certain herbs like thyme and sage.

Are carrots good companion plants for onions?

Yes, carrots make great companion plants for onions as they help deter carrot flies and don’t compete with your onion’s root system.

Can I plant chamomile near my onions?

Yes, chamomile is an excellent companion plant for onions as it attracts beneficial insects that help with pollination and natural pest control.

Can I plant beets near onions?

Yes, beets are great companion plants for onions as they help enhance each other’s growth through soil improvement.