What Not to Plant With Onions: A Gardening Guide

What Not to Plant With Onions?

When planting onions, it is best to avoid companion plants such as mustard greens, cabbage, cauliflower, broccoli, kale, collards, Brussels sprouts, tomatoes, peppers, eggplant, strawberries, potatoes, lettuce, parsnips, carrots, chamomile (unless desired flavor enhancement is desired), and roses (unless dealing with aphid infestation).

These plants can potentially compete for nutrients or attract pests that may harm onions.

Key Points:

  • Avoid planting mustard greens, cabbage, cauliflower, broccoli, kale, collards, Brussels sprouts, tomatoes, peppers, eggplant, strawberries, potatoes, lettuce, parsnips, carrots, chamomile, and roses with onions.
  • These companion plants can compete for nutrients needed by onions.
  • These plants also have the potential to attract pests that can harm onions.
  • However, chamomile can be planted alongside onions if a desired flavor enhancement is desired.
  • Similarly, roses can be planted with onions if dealing with aphid infestation.
  • It is best to consider these factors when planning the companion plants for onions.

Did You Know?

1. Onions emit a chemical known as allyl sulfide, which inhibits the growth of many different plants. It is advised not to plant onions with beans, peas, or asparagus, as these plants are particularly sensitive to allyl sulfide and may struggle to thrive when grown in close proximity to onions.

2. However, onions can actually have a positive effect when planted near certain companion plants. For example, onions are known to repel aphids, making them excellent companions for plants such as roses or broccoli which are prone to aphid infestations.

3. One lesser-known fact about onions is that they were widely used as a form of currency in ancient Egypt. The value of onions was so high that they were even used to pay workers who built the pyramids.

4. The pungent odor of onions not only repels insects but also some small mammals. For instance, placing onion peels or powdered onion at the entrances of burrows has been known to deter rabbits and moles.

5. Onions are fascinating plants as they belong to the allium family, which also includes garlic, leeks, and shallots. These plants are not only delicious but are also known for their health benefits, such as boosting the immune system and reducing the risk of certain diseases like heart disease and certain cancers.

Avoid Planting Brassicas With Onions

When it comes to planting onions, it is crucial to be aware of what plants should not be grown alongside them. One category of plants to avoid planting with onions is the Brassica family. This includes mustard greens, cabbage, cauliflower, broccoli, kale, collards, and Brussels sprouts. The reason for this is that these plants require similar nutrients as onions, resulting in competition for resources. Planting them together can lead to stunted growth and reduced yields for both crops.

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Additionally, certain pests and diseases tend to affect both onions and Brassicas. For instance, the onion fly is a common pest that can infest both crops, leading to significant damage. By separating them, you decrease the risk of pest infestations and allow for better crop management. It is wise to rotate your plantings each year, ensuring that onions and Brassicas do not share the same bed.

  • Avoid planting Brassicas alongside onions because they compete for nutrients.
  • Separating them decreases the risk of pest infestations like the onion fly.
  • Rotate your plantings each year to prevent crops from sharing the same bed.

Keep Nightshades Away From Onions

Another group of plants that should not be planted with onions are nightshades. This includes tomatoes, peppers, and eggplant. Nightshades require high levels of phosphorus, while onions prefer lower levels. Planting them together can lead to imbalances in soil nutrient levels, hindering the growth and development of both crops.

Moreover, nightshades are susceptible to diseases such as blight and various fungal infections. These diseases can easily transfer to the onions if they are grown in close proximity, causing damage and reducing yields. To maintain the health and productivity of both crops, it is best to keep nightshades and onions separate.

Onions And Leafy Greens Clash

When planning your garden, avoid planting onions alongside lettuce and Swiss chard. Onions are heavy feeders and require high nutrient levels, while leafy greens prefer a more moderate amount. Planting them together can result in uneven growth and nutrient deficiencies for both crops.

Onions and leafy greens may attract similar pests, such as aphids and thrips. These pests can cause damage to both crops if they are grown in close proximity. Separating these plants will minimize the risk of pest infestations and promote healthier growth.

Beware Of Planting Onions Near Root Vegetables

Onions and root vegetables, such as potatoes, parsnips, and carrots, should be kept separate in your garden. These plants have different root structures and growth habits. Onions have shallow roots, while root vegetables, like potatoes, have deeper and more extensive root systems. Planting them together can lead to competition for water and nutrients, resulting in reduced yields for both crops.

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Moreover, some root vegetables, like potatoes, release chemical compounds that can inhibit the growth of onions. This can affect the overall health and productivity of the onion plants. To ensure optimal growth for both crops, it is advisable to plant them in separate areas of your garden.

  • Onions and root vegetables should be kept separate due to different root structures and growth habits.
  • Onions have shallow roots, while root vegetables like potatoes have deeper and more extensive root systems.
  • Planting them together can result in reduced yields due to competition for water and nutrients.
  • Some root vegetables, such as potatoes, release chemical compounds that can inhibit the growth of onions.
  • To ensure optimal growth, it is advisable to plant them in separate areas of your garden.

“Onions and root vegetables, such as potatoes, parsnips, and carrots, should also be kept separate in your garden.”

Specific Exceptions When Pairing Onions With Other Plants

While there are several plants that should not be planted with onions, there are a few exceptions to consider. Although chamomile can affect the flavor of onions if planted nearby, some gardeners intentionally pair them to enhance the taste. If you desire a subtle chamomile flavor in your onions, consider planting them together.

Similarly, roses can be planted with onions to deter aphids. Aphids are known to infest roses, and the presence of onions can act as a natural repellent, keeping aphids away. This can help protect your roses and promote their healthy growth.

In conclusion, it is essential to avoid planting certain plants with onions to ensure healthy growth and successful yields. Here are some examples to keep in mind:

  • Brassicas
  • Nightshades
  • Leafy greens
  • Root vegetables

These should be kept separate from onions to prevent nutrient competition, disease spread, and hindered growth.

However, there are exceptions, such as pairing onions with chamomile for flavor enhancement or roses to deter aphids. By carefully planning your garden and following these guidelines, you can maximize the potential of your onion plants and enjoy a thriving garden.


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Frequently Asked Questions

What can be planted next to onions?

In addition to Brassica vegetables, there are other plants that can benefit from being planted next to onions. Carrots and beets, for example, are compatible companions for onions. The strong aroma of the onions may deter some pests that typically target these root vegetables, helping to keep them healthy and pest-free. Furthermore, lettuce and spinach can also thrive when grown alongside onions, as the onion’s insect-repelling properties may provide a natural defense against common pests that affect leafy greens. Overall, planting onions alongside a variety of vegetables can contribute to a more robust and naturally protected garden.

What does not like to be planted next to onions?

One plant that does not appreciate being planted next to onions is asparagus. Asparagus and onions have different growth habits and nutrient needs, which may lead to competition for resources. To ensure both plants thrive, it is recommended to keep them separate. Additionally, peas should not be planted near onions. As peas are legumes, they have a symbiotic relationship with nitrogen-fixing bacteria in their roots, whereas onions prefer a lower nitrogen content in the soil. Planting the two together may disrupt the nitrogen balance and negatively impact the growth of both plants.

Do onion plants like acidic soil?

Onion plants thrive in slightly acidic soil, making it an ideal condition for their growth. Well-drained and fertile soil is essential for these easy-to-grow plants. Incorporating organic matter, such as compost, can significantly improve heavy soils and provide the necessary nutrients for onion plants to flourish. With their higher fertility requirements, onions stand out among other vegetables but happily settle in slightly acidic environments.

Does light affect onions?

Yes, light indeed plays a significant role in the growth and development of onions. The duration and quality of light can have a substantial impact on the formation and maturation of onion bulbs. In short days, the process of bulb formation is inhibited, resulting in the absence of bulbs. Conversely, in long days, onions tend to form large bulbs, but they require more time to reach maturity. On the other hand, in very long days, onions produce smaller bulbs that mature relatively quickly. Therefore, understanding the effect of light on onions is vital for optimizing their growth and obtaining desired bulb sizes within specific timeframes.

References: 1, 2, 3, 4

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