Don't Grow These Plants Next to Each Other in Raised Beds – You’ll Ruin Your Homegrown Harvest

Raised beds make gardening wonderfully manageable. The soil warms quickly in spring, drainage is improved and the height of the beds makes tending and picking a breeze. Planting looks neat, contained and productive. But compatibility matters in a raised bed where roots are competing for nutrients and water in a limited volume of soil. The wrong choice of plants can lead to stressed plants, poor growth and ultimately a disappointing yield.

Companion planting is often referred to in helpful terms, but it is equally important to understand which plants should be kept apart. Some plants share pests and diseases, and in a container or raised bed, infestation could spread quickly. There are even plants that release natural chemicals from their roots that can stunt the growth of nearby plants.

If you want your raised beds to be attractive and productive, careful plant placement is essential. Thoughtful spacing and planning will make the difference between a productive bed and a disappointing one. Here are the combinations best avoided in raised beds, and some reasons why.

Tomatoes and White Potatoes

Both these crops belong to the Solanaceae (nightshade) family and are highly susceptible to Phytophthora infestans, a fungus responsible for white potato and tomato blight, a disease that spreads easily between the plants.

Planting these crops beside each other will increase the risk of disease spreading through the bed.

To keep your plants healthy, dedicated beds for each of these vegetables is essential, and these should be at a distance of at least 3 feet.

Note: Sweet potatoes, whilst sharing a similar name, are botanically unrelated to white potatoes and tomatoes. Sweet potatoes belong to the Convolvulacea (morning glory) family but still share some of the same pests and diseases and are therefore more suited to their own raised bed.

Peppers and Eggplants

These crops are also members of the nightshade family, and they too are susceptible to similar pests and diseases but luckily are less susceptible than tomatoes and white potatoes.

If well-spaced (about 1-2 feet apart), they actually make excellent raised bed companions since they have similar heat and moisture requirements. However, because of their relation to tomatoes and white potatoes, it’s best not to plant them nearby, as this will increase the risk of pest transfer.

In addition, you should avoid planting tomatoes in soil that has been used to grow white potatoes, peppers or eggplant in previous years, and similarly, don’t plant potatoes where tomatoes, peppers or eggplants have been.

Rotating these crops prevents the build-up of diseases and ensures that soil nutrients are not depleted. A soil nutrient probe, such as this handy one from Amazon, can help you to check the levels, so that you'll know exactly when a nutrient boost is needed.

Corn and Tomatoes

These crops will compete for sunlight as well as nitrogen in the soil, and are not good raised bed companions.

The tall corn stalks will shade the tomatoes and inhibit growth. They also share the same pest. Did you know that corn ear-worm and tomato fruit-worm are the same critter – also known as Helicoverpa zea.

Keeping corn and tomatoes apart will reduce the risk of these plants becoming infected and damaged.

You can find better corn companion plants in our dedicated feature. You can also find 'Golden Bantam' corn seeds available from Amazon.

Fennel and Salad Crops

Fennel is well-known for its allelopathic properties and is best left in its own container or separate raised bed. The compounds released from the roots of fennel will inhibit the growth of many vegetables.

Don’t be tempted to plant salad veggies such as lettuces and cucumbers alongside herbs such as rosemary, thyme and sage.

Lettuces and cucumbers like a lot of moisture, whilst these dry-loving herbs prefer drier, well-drained conditions. Better planting companions would be parsley, dill or basil, all of which require more moisture.

Mint is a hugely invasive herb and needs to be contained in its own sturdy individual pot or planter. Their underground stems, known as rhizomes, have a horizontal habit and will aggressively invade any soil they can find.

Mint will out-compete other plants and is extremely difficult to remove once it’s taken hold. A plastic pot, such as this budget-friendly option from Amazon, will contain mint more effectively than terracotta or a wood or metal planter. If you want to plant mint in your raised bed, sink a sturdy plastic pot into the soil first.

Too Much Competition

Planting onions, garlic, leeks and chives with legumes such as beans and peas is a bad idea.

These plants will out-compete each other because legumes rely on nitrogen-fixing bacteria in their roots. Onions and garlic can inhibit this process and lead to weaker legume growth.

The allelopathic properties of the allium family (which includes onions, leeks, chives and garlic) means that the chemicals released from their roots can actually inhibit germination and stunt the early growth of beans and peas.

However, if you are wondering what does make a good planting companion with veggies from the allium family, look to leafy greens such as lettuces, spinach or kale. Similarly, herbs will grow well near the allium family, as will root crops.

Other plants that over-compete are members of the Cucurbitaceae (gourd) family – squashes, melons, and zucchini all come under this umbrella. These aggressive growers will overwhelm each other, and their large leaves cast shade onto other plants meaning that they require their own raised bed and lots of space to grow.

Raised beds reward thoughtful planning. While it’s tempting to tuck plants wherever there’s space, understanding how they interact below ground and how pests move between them can save you a season of frustration.

Keep heavy feeders apart, separate crops that share diseases, and isolate allelopathic plants. With careful placement, your raised beds will be healthier, more balanced, and far more productive from spring through fall.

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