onions companion planting
Organic Gardening - Organic Gardening Pest Control

Companion Planting Onions: Best Partners for a Healthier Garden

Companion planting is a tried and true gardening method that involves strategically grouping certain plants together to enhance growth, deter pests, and encourage healthy harvests. When it comes to onions, choosing the right companion plants is particularly beneficial. Onions release certain compounds that can deter pests and diseases, making them valuable allies in the garden. By understanding which plants are compatible with onions, gardeners can create a more productive and less maintenance-intensive garden.

While the benefits of companion planting are numerous, it’s equally important to be aware of which plants could be detrimental to onions. Some plants may compete with onions for resources or attract pests that could harm them. Additionally, planning the garden layout with companion planting in mind optimizes the conditions for onions and their companions. This careful planning can lead to better growth conditions, improved pest management, and ultimately, successful harvesting and storage of the crops.

Key Takeaways

  • Companion planting with onions can enhance garden health and yield.
  • Selecting the right plant partners is crucial for maximizing benefits.
  • Proper planning and knowledge of companions mitigate pest issues and resource competition.

Table of Contents

Companion Planting Fundamentals

Companion planting leverages the synergistic properties of different plants to enhance garden health and productivity. It differs from the current common practice in many commercial agricultural operations, or factory farms, that use the technique of monocropping.

Monocropping is the planting and growing of a single crop. Each year, these single crops are grown over and over again. Although the practice was established with good intentions, they have proven to be disastrous to the soil and its biodiversity, diversity in beneficial insects such as pollinators, contamination of the soil and water due to the heavy administration of herbicides and pesticides, as well as other environmental impacts.

Find out more about monocropping on the Food Revolution Network’s post about it.

Companion planting is not a new concept. It’s a method that’s been used for centuries. This section outlines why onions are prime candidates for companion planting and the guiding rules to follow.

Benefits of Companion Planting with Onions

Onions, with their pungent aroma, are excellent in deterring common pests, thereby acting as natural protectants for nearby plants. For instance, they can be effective in repelling aphids, which are a common threat to many garden vegetables. By integrating onions among carrot plants, gardeners can reduce the need for chemical pesticides, as the strong scent of onions disrupts the ability of carrot flies to locate their preferred host.

In addition to pest control, onions can improve the overall health of the garden ecosystem. They are known to form beneficial relationships with a variety of plants, including tomatoes, peppers, and cabbage, promoting vigorous growth and better yields.

Basic Principles of Companion Planting

When engaging in companion planting, there are a few principles to keep in mind to ensure success:

  • Diversity: A diverse garden mimics natural ecosystems, creating a more resilient growing environment. Introducing onions to a garden space can contribute to this diversity.
  • Spacing: Proper spacing is vital as it allows individual plants enough room to grow without competing for resources. Onions should be spaced in such a way that both they and their companions receive adequate water, sunlight, and nutrients.
  • Layering: Consider the height and structure of plants. Tall plants can provide shade for lower-growing, shade-tolerant species, while onions can be planted in the understory of taller plants without hindering their growth.

By following these principles, gardeners can ensure that their use of onions in companion planting brings the best possible outcomes for their gardens.

Best Companion Plants for Onions

When considering companion plants for onions, gardeners should focus on species that deter pests, do not compete for resources, and can even enhance the growth and flavor of onions.


  • Root Vegetables: Vegetables such as carrots and beets thrive when planted with onions. Their root systems occupy different soil levels which prevents competition for nutrients.
  • Leafy Greens: Lettuce is an excellent companion, as the onions help deter pests, ensuring healthier lettuce leaves.
  • Brassicas: Members of the brassica family, including kale, cabbage, broccoli, and cauliflower, benefit from the pest-deterring properties of onions.


  • Chamomile and Summer Savory: These herbs can enhance the growth and flavor of onion plants. Additionally, chamomile can attract beneficial insects to the garden.
  • Parsley: This herb can contribute to a mutually beneficial relationship when grown with onions, helping to deter pests.


  • Marigolds: These vibrant flowers are well-known for their pest-control properties and can protect onion plants from nematodes.
  • Nasturtiums: With their ability to repel numerous pests, nasturtiums are a valued companion for onions, as well as adding a splash of color to the vegetable garden.

I’ve compiled 7 plants that are onion friendly to give you a head start in your garden.

Onions and Carrots Companion Planting

These two vegetables are a great pair. Since onions have a strong, pungent aroma to them, they provide a natural deterrent for carrots. They’re able to deter the carrot fly. To me these initially didn’t seem like they would be companions since they’re both root vegetables. But as mentioned above, their roots don’t disturb one another.

Onions and Peppers Companion Planting

I find that peppers can actually be finicky. They’re easy to grow, but they require a little finesse. What’s worked best for me is making sure they get plenty of sun, but also a break from the intense heat of the day. Onions and peppers are the perfect pair. Both of these vegetables don’t require a ton of room. In addition to that, onions deter aphids, slugs, and cabbage worms that affect peppers. 

Onions and Broccoli Companion Planting

In my experience, broccoli can be a pain to grow. They can be affected by lots of pests. If you don’t stay on top of their care, they can easily become inundated. The best time to grow this crop is during the cool weather, which helps with stress from pests. They can be affected by aphids, cabbage loopers, cabbage root maggots, cabbage worms, stink bugs, and white flies. Planting these two plants together helps to repel the pests that affect broccoli.

Cucumbers and Onions Companion Planting

Cucumbers are one of the easiest crops to grow and if they’re given the right conditions, they’re also high yielding.  They can take up quite a bit of room, especially if they’re a vining variety. Vining varieties have a tendency to grow all over the place. I let them grow as they please and don’t cut them back. They thrive in the heat, the sun, and love water. Cucumbers can also be affected by a wide variety of pests like aphids, squash bugs, slugs, and more. As with all of the other vegetables that onions are planted with, they help deter pests that affect cucumbers.

Companion Planting Beets and Onions

These are both another pair of root vegetables that prefer the same soil conditions. Onions are able to repel pests like cutworms, borers, aphids, and flea beetles that affect beets.

Companion Planting Kale and Onions

Kale is another cool weather crop that can be affected by a lot of pests. They’re affected by pests like butterflies, aphids, and flea beetles. They can quickly become inundated if they’re not kept in check. Ideally, kale should be grown under cover to avoid having to deal with the amount of pests it can suffer. However, you can also plant onions alongside it to deter pests.

Parsley and Onions Companion Planting

Parsley is an easy plant to grow. What’s great about parsley is that it actually tastes better in colder weather and when it’s had a light frost. It’s a nice crispy, fresh taste that is amazing and so much better than when it’s grown during the warmer months.  There’s a good relationship between parsley and onions. Parsley helps onions out by warding off onion flies.

Plants to Avoid Near Onions

While onions are versatile companions in the garden, not all plants are beneficial to grow in close proximity to them. Certain species may compete with onions for resources or have negative allelopathic interactions, inhibiting each other’s growth. I’ve compiled 6 plants that don’t mesh well with onions. It’s always super important to know each plant’s growing conditions to make sure that they don’t counteract each other. The below list is not all inclusive of what plants to avoid near onions.

Onions and Tomatoes Companion Planting

There is mixed information that I’ve found about companion planting with onions and tomatoes. Although they can be planted together and make a good pair, if there are issues with pests like thrips, they should not be planted together. For this reason, I’d probably just avoid planting them together to avoid any issues.

Onions and Beans Companion Planting

Beans and onions just don’t mix together very well. Beans have a shallow root system that does not like to be disturbed, just like peas. If their roots are disturbed, they can be easily damaged. Once the roots become damaged, the whole plant can die very quickly. They can also require more frequent waterings because of their shallow root system. This may not bode well with onions which aren’t good at taking up water. Additionally, onions may even affect the taste of the beans.

Onions and Peas Companion Planting

They do not pair well with onions. The growth of these legumes can be stunted due to the antibacterial properties of onions, which can interfere with the nitrogen-fixing bacteria beneficial to beans and peas. Peas also have very sensitive roots. If they’re disturbed, they’ll easily die off. Like beans, peas may need more frequent waterings because of their shallow root system. Frequent waterings may not go well for onions. Onions and peas therefore have different growing needs. Alliums in general stunt the growth of peas. They may even make the plants more susceptible to pests and diseases.

Asparagus and Onions Companion Planting

Onions and asparagus compete for the same nutrients and are likely to inhibit each other’s growth when planted too close together. Asparagus have a deep root system compared to beans and peas. Onions can inhibit their growth by stunting them and alter their flavor. They also do not benefit one another in any way.

Sage and Onion Companion Planting

Sage is a vigorous grower which is great because you get a high yield with a minimal amount of seeds planted. This herb has an allelopathic effect on onions, meaning substances released by sage can inhibit onion growth. Although sage is known to stimulate growth for a wide variety of vegetables, onions just aren’t one of them. Keep these two far away from each other.

Onions and Squash Companion Planting

There was mixed information found about planting onions and squash together. So I’ll advise you to use caution when doing so. The pro about planting them together is that onions repel pests that affect squash. The cons are that they can affect the taste of the squash and may disturb their roots. So you may need a bit of room between them.

Designing Your Garden Layout

When planting onions, efficient use of space and consideration of sunlight are crucial for a thriving garden.

Spacing and Arrangement

Onions require adequate room to grow and should be spaced about 4 to 6 inches apart in rows. The rows should be separated by 12 to 18 inches to allow for proper air circulation and ease of maintenance. Gardeners should plant onions in blocks or rows rather than scattering them throughout the garden to take advantage of their pest-deterring properties and create a supportive environment for companion plants.

Sunlight and Shade Considerations

They thrive in an area that receives full sunlight, with a minimum of 6 hours of direct sunlight each day. If certain companion plants need less sunlight, they should be strategically positioned to the north of onions to avoid shading. Onions are resilient and can tolerate partial shade, but this may affect bulb development. Avoid placing taller crops to the south of onions to prevent unwanted shade.

Optimizing Growth Conditions

To achieve the best results in onion companion planting, pay careful attention to soil composition and watering practices. These factors are crucial for the overall health of onions and their companion plants. I’m also going to share a technique that I learned to get a nice size bulb. 

Soil Composition and Nutrition

Onions thrive in soil that is well-drained and rich in organic matter. Aim for a soil pH between 6.0 and 7.0. Before planting, it is beneficial to incorporate compost to enhance soil fertility. This not only provides a steady supply of nutrients but also improves soil structure, which is essential for root growth.

Adding aged manure or compost can provide the necessary nutrients for onions and its companions. Mulching with organic materials such as straw can retain moisture and suppress weeds, contributing to a more suitable growing environment.

Watering Practices

Onions require consistent moisture to develop properly, less so when the bulbs begin to mature. Overwatering can lead to root rot, while under-watering can stress the plants and reduce yield.

Consider using drip irrigation or soaker hoses to deliver water directly to the roots and avoid wetting the foliage, which can lead to fungal diseases. Monitoring soil moisture with a finger or moisture meter ensures onions are not waterlogged or dehydrated.

Spooning the Bulb

A technique I learned in the past couple of years is known as spooning the bulb. The root bulb doesn’t like to be constricted and requires loose soil for a nice big shape. Compact soil restricts the bulb and it’ll remain small. As the plant is growing, take a spoon, or simply use your hand, to loosen up the soil around the bulb. I create a circle around the bulb about half way down. Be careful not to remove too much soil around the bulb so as not to disturb it.

Pest and Disease Management

In the domain of onion companion planting, certain plants serve dual functions: they act as natural repellents for pests and serve as indicator plants for potential diseases. Strategic placement of these companions can significantly reduce the need for chemical interventions.

Natural Repellents

Onions themselves can deter various pests due to their strong scent. Carrots are often planted alongside onions, as onions can repel the carrot fly, while carrots can help ward off the onion fly. Plants such as chamomile and summer savory are known to enhance onion growth and health by deterring harmful insects and attracting beneficial ones.

Beneficial combinations include:

  • Onions with Chamomile
  • Onions with Summer Savory
  • Onions with Carrots

Indicator Plants

Indicator plants signal the presence of pests or diseases before they become rampant, providing an early warning system to gardeners. For instance, if leeks, which are susceptible to onion flies, begin to show signs of stress, it might indicate a burgeoning problem for the onions as well. Planting leeks near onions can thus help in monitoring and mitigating pest infestations early on.

By integrating these practices into their gardening, individuals can uphold the health of their onion crops and surrounding plants, ensuring a bountiful harvest.

Harvesting and Storage Tips

Successful onion companion planting culminates in proper harvesting and storage practices to maximize the yield’s longevity and flavor.

Harvesting Best Practices

Harvest  onions when approximately half the tops have fallen over and begun to yellow. This indicates that the bulbs have ceased growing and are ready for harvest. The ideal time for this process is often late summer, before the cool weather sets in. To avoid damage, be gentle when pulling the onions from the soil. It’s beneficial to use a digging fork to loosen the earth around the bulbs. However, be careful using any tools so as not to damage the onion bulb.

Steps for Harvesting Onions:

  1. Check the Tops: When they start to fall over and brown, onions are ready.
  2. Loosen the Soil: Gently use a fork to lift the onions.
  3. Pull Gently: Extract the onion, taking care not to bruise the bulb.
  4. Dry & Cure: Lay them out in a warm, dry, well-ventilated area away from direct sunlight for several weeks.

Reference: When to Harvest Onions

Post-Harvest Storage

Once onions are harvested and cured, storage becomes the next critical step. They should be stored in a cool, dry place with good air circulation. Ideally, temperatures should be between 40-50°F (4-10°C) with relative humidity around 70%. Onions can be stored in mesh bags or nets to facilitate airflow. It is crucial to avoid storing them in plastic bags or any container that restricts air movement, as this can accelerate molding and spoiling.

Properly stored onions can last for several months, providing a lengthy shelf life for the harvested crop.

Key Storage Conditions:

  • Temperature: 40-50°F (4-10°C)
  • Humidity: Approximately 70%
  • Airflow: Store in mesh bags or nets, not plastic

Frequently Asked Questions

In the context of companion planting, certain pairings can enhance growth, deter pests, and maximize space. Below are answers to common questions about companion planting with onions.

Which vegetables make the best companions for onions in the garden?

Vegetables like carrots, lettuce, and beets are excellent companions for onions. They coexist well due to complementary growth habits and pest deterrence.

Are there any plants that should be avoided when companion planting with onions?

Beans and peas do not pair well with onions. Their growth can be inhibited due to biochemical incompatibilities between these plants.

What are the benefits of growing onions alongside carrots?

Onions can deter the carrot fly from attacking carrot crops, as the strong scent of onions masks the presence of carrots.

How does companion planting affect the growth of onions and tomatoes?

Tomatoes and onions are not ideal companions; both require different watering levels, and close proximity may lead to competition for nutrients.

Which herbs can be planted with onions to enhance garden health?

Herbs such as chamomile and summer savory can promote onion growth and enhance flavor, while also attracting beneficial insects.

Can onions and peppers be grown in close proximity without negative effects?

Onions and peppers can be grown together without adverse effects, as onions may help repel certain pests that harm pepper plants.

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