Mad About Berries

Onion Companion Plants

Companion planting is an old practical strategy for enhancing plant health, optimizing space, and increasing the harvest. Among the many candidates for companion planting, onions are particularly favorable due to their ability to coexist beneficially with a variety of other plants. 

Whether you are a novice or a seasoned gardener, understanding which plants to pair with your onions can transform your garden into a more productive and vibrant ecosystem.

Published: May 7, 2024.

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Introduction to Companion Planting

Companion planting is an age-old agricultural practice that involves the strategic placement of different crops near one another to enhance growth, yield, and pest control.

By understanding the natural affinities between certain plants, gardeners, and farmers can create a more harmonious garden ecosystem that promotes healthy growth and sustainable practices.

Overview of Companion Planting

The principle behind companion planting is that certain plants can benefit others when grown in close proximity. These benefits include improved nutrient uptake, pest and disease control, and better use of space.

The right plant combinations can deter pests, attract beneficial insects, and even enhance the flavor and growth rate of neighboring plants.

Benefits Specific to Onions

Onions are particularly receptive to companion planting. They can benefit significantly from the presence of certain plants, which help repel onion pests such as aphids, onion flies, and certain types of fungi.

Companion plants can also help onions by enhancing soil structure and nutrient availability. Furthermore, because onions have shallow roots, they can share space with deeper-rooted plants without competing for resources.

Why Onions Benefit from Companion Planting

Improving Soil Health

Onions, being shallow-rooted, benefit from having companion plants that can help maintain soil structure and reduce erosion. Deep-rooted companions can bring nutrients from deeper in the soil closer to the surface, making them more accessible to onion plants.

This symbiotic relationship helps maintain a healthy soil ecosystem, which is essential for sustainable gardening.

Pest and Disease Management

One of the most significant advantages of companion planting for onions involves natural pest and disease control. Certain plants emit odors or chemicals that can repel onion pests or attract beneficial insects that prey on onion pests.

Such biological control reduces the need for chemical pesticides, promoting a healthier garden environment.

Maximizing Garden Space

Companion planting with onions allows gardeners to use their garden space more efficiently. Onions can be interspersed among other plants, utilizing the available space more effectively and increasing overall productivity. This is especially beneficial in small gardens where space is at a premium.

Best Companion Plants for Onions


Carrots are excellent companions for onions because they can help break up the soil with their deeper roots, making it easier for onion roots to grow. The scent of onions also deters carrot flies, while the smell of carrots can repel onion flies, creating mutual protection.

Planting carrots and onions together should be done with adequate spacing to allow for root development and air circulation.

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Lettuce and onions make for ideal companions as lettuce has shallow roots and requires less space, allowing onions to utilize the underground area more effectively.

The quick maturity of lettuce also means it can be harvested before onions need more room to expand, making this pairing particularly space-efficient.


Strawberries can benefit from the onion's ability to deter common pests like slugs, which are known to damage strawberry leaves and fruits.

In return, strawberries cover the ground, reducing weed growth and helping to maintain moisture levels in the soil, which benefits the onions.


Spinach benefits from being planted near onions because the onions help to deter many pests that might otherwise target spinach plants. The strong scent of onions can repel aphids and other insects, providing a natural form of pest control that reduces the need for chemical interventions.

Additionally, since spinach has a relatively short growth cycle and different nutrient demands, it doesn't compete heavily with onions, allowing both plants to thrive without inhibiting each other's growth. This makes them an excellent pairing in a space-efficient garden.


The strong scent of onions can help deter common pests like cabbage worms, aphids, and flea beetles that typically target cabbage and other brassicas.

This natural pest repellent effect reduces the need for chemical pesticides, making your garden safer and more sustainable.
Additionally, onions and cabbage have different root depths, which means they don’t compete significantly for nutrients and water, allowing them to coexist harmoniously in the garden.

This pairing not only improves pest management but also optimizes the use of garden space.


Nasturtiums are known for their ability to repel a wide range of pests, including aphids and beetles, which can benefit the onions growing nearby.

They act as a trap crop, attracting pests away from onions and other vegetables.

Additionally, the bright flowers of nasturtiums can attract beneficial insects that prey on common pests, further enhancing the garden's natural pest management.

Their sprawling growth can also help suppress weeds, reducing competition for nutrients and keeping the soil moist, which benefits the onions.

This combination of pest control and ground cover makes nasturtiums a valuable ally in the companion planting garden.


Dill is another good companion for onions but with some considerations. Dill can attract beneficial insects such as wasps and ladybugs that prey on common garden pests, including those that might affect onions. These beneficial insects help to naturally control pest populations, reducing the need for chemical pesticides.

However, dill can be somewhat allelopathic to some plants, meaning it might inhibit the growth of plants nearby due to the release of certain chemicals. While this effect is not strongly detrimental to onions, it is something to be aware of if you plan on planting dill near other more sensitive crops.

If you decide to use dill as a companion plant for onions, it's a good idea to monitor their interaction closely and possibly provide some space between dill and other more sensitive plants in your garden.

Other Compatible Plants

Other excellent companions for onions include:

  • Tomatoes: Their tall structure can provide shade for onions, reducing water evaporation from the soil.
  • Chamomile: Known to improve the flavor of onions and attract beneficial insects.
  • Beets: Share similar soil and water needs, making them low-maintenance companions.

Using these planting strategies not only maximizes the health and output of your garden but also promotes a biodiverse ecosystem where plants support each other’s growth and vitality.

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Plants to Avoid Pairing with Onions

While companion planting can have many benefits, it is equally important to be aware of plant combinations that can be detrimental. Certain plants can negatively affect onions by competing for resources, attracting pests, or through chemical antagonism.

Reasons Certain Plants Hinder Onion Growth

Plants might inhibit onion growth by:

  • Competing for space, light, or nutrients: Some plants have growth habits or root systems that overpower the relatively modest needs of onions.
  • Attracting pests that harm onions: Although some plants can repel pests, others might attract pests that are harmful to onions.
  • Chemical Interference: Certain plants release chemicals that can inhibit the growth of nearby plants, a phenomenon known as allelopathy.

Specific Examples and Explanations

  • Beans and Peas: Legumes such as beans and peas are generally poor companions for onions. They can add too much nitrogen to the soil, which can inhibit the growth of onion bulbs and lead to more foliage.
  • Sage: This herb is known to release chemicals that may inhibit the growth of onions. Keeping sage and onions apart ensures that both plants can thrive without chemical interference.
  • Asparagus: Asparagus and onions do not cohabit well because they can foster the same type of root rot, potentially devastating both crops.

Designing Your Garden Layout

Creating an effective garden layout involves considering the specific needs of each plant, including sunlight, space, and water requirements. When planting onions with their companions, thoughtful planning can maximize garden efficiency and yield.

Practical Tips for Interplanting

  • Use raised beds or rows: These can help manage different plant species' varying root depths and nutrient needs.
  • Rotate crops: This prevents soil depletion and reduces the build-up of pests and diseases.
  • Observe the mature size of plants: Ensure that each plant has enough room to grow to its full size without overcrowding.

Visual Guide to Spacing and Placement

  • Onions and Carrots: Plant onions and carrots in alternate rows, with about 3-4 inches between plants within the row. This spacing helps prevent competition and maximizes the pest deterrence effect.
  • Onions and Lettuce: Plant lettuce between onion rows. Lettuce can be harvested before onions fully mature, making efficient use of space and time.
  • Onions and Strawberries: Maintain a distance of at least 12 inches between strawberry plants and onion sets to ensure adequate space for growth and air circulation.

Caring for Your Onion Companion Garden

To ensure a healthy and productive garden, proper care involving watering, fertilization, and pest management is crucial.

Watering Needs

  • Regular and even watering: Onions require consistently moist, but not waterlogged, soil. Use mulch around the plants to help retain soil moisture and reduce water needs.

Fertilization Methods

  • Balanced approach: Use a balanced fertilizer that does not promote excessive nitrogen, as too much can encourage leaf growth at the expense of the bulbs.
  • Compost and organic matter: Adding compost can provide a slow-release source of nutrients and improve soil structure.

Pest Management Strategies Specific to Companion Setups

  • Barriers and traps: Use physical barriers like row covers to protect young onion plants from pests.
  • Natural repellents: Planting marigolds or garlic near onions can help repel certain pests.
  • Biological control: Encourage beneficial insects by planting flowers like calendula and alyssum that attract predators of common pests.

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Pairing the right companions with onions can significantly enhance your garden's health and yield.

Planting compatible fruits and veggies like carrots, lettuce, and strawberries, every gardener can naturally fend off pests, improve soil conditions, and make efficient use of your gardening space.

On the other hand, avoiding incompatible plants such as beans and sage helps ensure that the onions thrive.

Implementing these companion planting strategies not only boosts the onion crop but also contributes to a more diverse and sustainable garden environment.

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