How to Companion Plant Onions

For thousands of years, gardeners have been observing their gardens and experimenting with companion planting. Much of what we know about companion planting onions and other crops comes from years of observation and more recently some more scientific studies. I’ve been experimenting with companion planting in my own garden for many years and follow a few simple methods that have improved my garden and the amount of produce my garden yields. In this guide we’ll explore how to companion plant onions.

I’ve found onions to be an important companion plant in the garden. Instead of growing one row or bed for my onions, I like to place them in a few groups around the garden alongside things like carrots and beets.

You can also find more general information about companion planting see our chart.

Contents

What to Know about Onion Companion Planting

Companion planting involves strategically growing different plants together to enhance growth, deter pests, and promote a healthy garden ecosystem.

By using the natural synergy that exists between plants, this method boosts yields and creates stronger plant growth without the need for synthetic pesticides or fertilizers.

For onions, some plants are beneficial companions, like carrots and beets, which help repel pests. On the other hand, there are certain plants, such as garlic and chives, can hinder onion growth by competing for resources. I recommend separating onions from other Allium family members.

Companion planting with onions encourages biodiversity, attracts beneficial insects, and reduces reliance on synthetic chemicals, promoting a sustainable garden environment.

The Best Onion Companion Plants for Onions

Below are a list of the best companion plants for onions based on research and practice in my own garden. I recommend experimenting with these combinations yourself as there are many other factors that impact how plants interact including your climate, soil, and specific space.

Carrots: Carrots are one of the most well-known companions for onions. They help repel pests such as onion flies and carrot flies, while onions deter carrot flies in return. Additionally, carrots and onions have different root depths, reducing competition for nutrients.

Beets: Beets are beneficial companions for onions because they repel pests like onion flies and also benefit from the odor of onions, which masks their scent from pests. Beets also have a shallow root system, so they don’t compete much with onions for nutrients.

Lettuce: Lettuce provides a living mulch around onions, helping to retain soil moisture and suppress weeds. It also attracts beneficial insects such as ladybugs and parasitic wasps, which prey on pests harmful to onions.

Spinach: Spinach is another good companion for onions because it helps to shade the soil, keeping it cool and moist, which onions prefer. Spinach also attracts beneficial insects like predatory mites and lacewings.

Chamomile: Chamomile has insect-repellent properties that can help protect onions from pests like aphids and thrips. It also adds nutrients to the soil as it decomposes, benefiting the onions.

Lavender: Lavender repels pests such as moths and fleas, which can be harmful to onions. Its foliage also adds beauty to the garden while deterring pests.

Bad Companion Plants with Onions

Members of the Allium Family: Plants such as garlic, chives, and leeks are not suitable companions for onions because they compete for similar resources, including nutrients and space. Additionally, they may attract the same pests and diseases that affect onions. This is the combination I try to avoid the most.
Beans: Beans, including both bush and pole varieties, are not ideal companions for onions. They have a dense root system that can compete with onions for water and nutrients. Additionally, beans fix nitrogen in the soil, which can lead to an excess of nitrogen that may inhibit onion bulb formation.
Peas: Peas, like beans, fix nitrogen in the soil and may compete with onions for nutrients. They also have a climbing habit that can shade onions, potentially reducing their growth and yield.
Brassicas: Plants in the brassica family, such as cabbage, broccoli, and kale, are not recommended companions for onions. They may attract similar pests like cabbage worms and onion maggots, leading to increased pest pressure on both crops.
Fennel: Fennel produces compounds that inhibit the growth of other plants, including onions. Planting onions near fennel can result in stunted growth and reduced yields for both crops.
Potatoes: Potatoes are not ideal companions for onions because they have similar growing requirements and may compete for space and nutrients in the soil. Additionally, potatoes are susceptible to diseases like late blight, which can spread to onions if planted nearby.

Avoid planting these plants near onions to limit competition and reduce the risk of pest and disease problems in your garden.

Step by Step Plan for How to Companion Plant Onions

Once you’ve done some research, it’s time to put companion planting into action. Below is a step by step guide to get you started.

Choose Beneficial Companions: Select plants that have symbiotic relationships with onions and help repel pests. Good companions for onions include carrots, beets, lettuce, and spinach.
Plan Your Garden Layout: Design your garden layout to maximize the benefits of companion planting. Consider the space available and arrange companion plants around onions in a way that optimizes their growth and interaction.
Interplant Companion Plants: Plant companion plants alongside onions, ensuring they are close enough to provide mutual benefits but not too close to compete for resources. Aim for a diverse mix of companion plants to support a healthy garden ecosystem.
Utilize Interactions: Take advantage of the natural interactions between companion plants and onions. For example, carrots and beets release substances that deter pests harmful to onions, while also providing structural support and conserving moisture in the soil.
Avoid Negative Companions: Be mindful of plants that can hinder onion growth. Avoid planting members of the Allium family, such as garlic and chives, near onions, as they may compete for resources and space.
Maintain Garden Health: Regularly monitor your garden for pests and diseases. Practice good garden hygiene, such as removing weeds and dead plant matter, to reduce the risk of pest infestations and promote a healthy garden environment.