Why Can't You Plant Tomatoes Next to Onions

Plants are known to thrive in groups that are beneficial to one another. However, not every plant benefits its neighbors. Tomatoes and onions are a perfect example of plants that do not get along. Despite being popularly grown in home gardens, tomatoes and onions should never be planted next to each other. In this article, we explore the reasons behind this advice and the scientific explanations behind it.

The Allium Family and Tomatoes

Onions, leeks, chives, and garlic belong to the Allium family. Members of this family are known to release a chemical called allicin into the soil. This chemical can inhibit the growth of neighboring plants. Tomatoes, on the other hand, are highly sensitive to this chemical. When exposed to allicin, they tend to be stunted and may fail to produce properly.

Fungal Diseases

Tomatoes and onions are both susceptible to fungal diseases. When planted too close to each other, fungal spores from one plant can easily spread to the other. For example, the fungus that causes gray mold in tomatoes can easily spread to adjacent onions. This can lead to a complete loss of the crop.

Water and Nutrient Competition

Tomatoes and onions have different needs when it comes to water and nutrients. Tomatoes require a lot of water and nitrogen, while onions prefer a drier soil and require more phosphorus and potassium. When planted together, they compete for these resources, leaving one plant nutrient-deprived. This can affect the quality and quantity of the harvest.

Companion Planting

Companion planting is a gardening technique where plants with mutually beneficial characteristics are grown together. For example, plants that attract beneficial insects can be planted alongside those that need insect pollination. However, companion planting should not involve onions and tomatoes. Instead, they should be grown in separate areas of the garden or spaced out by at least four feet to avoid cross-contamination.

Conclusion

In summary, while tomatoes and onions may be popular home garden crops, they should not be planted next to each other. The release of allicin from onions, susceptibility to fungal diseases, competition for resources, and the lack of mutual benefits in companion planting make it best to keep these two crops separate. By doing so, you can maximize the yield of both plants, avoid crop failure, and improve the overall health of your garden.