Companion planting involves strategically positioning different plant species near one another to foster a mutually beneficial environment. This technique is particularly effective in the vegetable garden for maximizing the health and yield of primary crops like tomatoes. By creating a diverse ecosystem, gardeners can naturally manage pests, improve soil quality, and enhance plant vigor. Selecting neighbors that complement the tomato plant’s needs turns a simple row of vegetables into a dynamic and productive polyculture.
Plants That Help Tomatoes Thrive
Plants that benefit tomatoes often fall into categories based on their primary function, whether it is repelling harmful insects or improving the soil structure around the tomato roots. French marigolds are valued for their ability to combat microscopic pests in the soil. Their roots release a chemical known as alpha-terthienyl, which is toxic to root-knot nematodes that commonly attack tomato roots and compromise nutrient absorption. Interspersing these flowers throughout the tomato patch helps establish a chemical defense zone below the soil surface.
Herbs with strong scents are effective against various above-ground pests. Basil, a classic culinary partner, helps repel tomato hornworms and thrips, possibly by masking the tomato plant’s scent. Basil also encourages healthier growth in the tomato plant. Similarly, members of the Allium family, such as chives and garlic, emit sulfurous compounds that deter aphids, spider mites, and Japanese beetles from settling on the foliage.
Other companions function to attract beneficial insects that prey on tomato pests. Borage, a flowering herb, attracts pollinators and helps deter the destructive tomato hornworm. When allowed to flower, parsley and dill attract parasitic wasps, which lay their eggs inside pest caterpillars. Low-growing root vegetables like carrots also help the tomato by aerating the soil. Their deep, slender roots break up the surrounding earth, increasing water and oxygen penetration for the tomato’s root system.
Plants to Never Plant Near Tomatoes
Just as some plants offer support, others can actively harm tomatoes and should be kept at a distance. Certain plants release allelopathic chemicals, which are natural compounds that inhibit the growth of surrounding vegetation. Fennel, for example, secretes substances from its roots that stunt the development of nearly all neighboring plants, including tomatoes. Any planting that includes fennel should be isolated to a dedicated area of the garden.
Other detrimental pairings are due to competition for resources or shared susceptibility to disease. Members of the Brassica family, which includes cabbage, broccoli, and cauliflower, are heavy feeders that aggressively compete with tomatoes for soil nutrients like nitrogen and phosphorus. When grown too close, this competition can result in significantly smaller tomato harvests and overall stunted plant growth. Corn is another poor companion because it is a tall, heavy feeder that competes for light and water.
Plants in the same nightshade family as tomatoes, such as potatoes and eggplants, pose a different kind of risk. Because they share a similar genetic makeup, they are vulnerable to the same pests and soil-borne diseases, most notably early and late blight. Planting them together creates a high-risk environment where disease can spread rapidly and multiply, potentially leading to the loss of both crops. To prevent this buildup of shared pathogens, these relatives should be rotated to separate sections of the garden each year.
Strategic Placement of Companion Plants
The physical arrangement of companion plants is as important as their selection. For pest-repelling flowers like marigolds, intercropping is the most effective strategy, requiring them to be planted directly within the tomato rows. This distributes the protective root chemicals and scents across the entire planting area. Conversely, for trap crops like nasturtiums, a perimeter planting or border is more suitable, as the goal is to lure pests away from the main crop.
Low-growing herbs and greens, such as basil and lettuce, are ideal for planting directly beneath the tomato canopy. This arrangement maximizes space by utilizing the lower light conditions and helps retain soil moisture by acting as a living mulch. When growing in containers, a single tomato plant can be surrounded by three or four small companion herbs. Tall, vertical companions must be managed carefully to ensure they do not cast excessive shade on the sun-loving tomato plants. They can be planted on the north side of the garden to provide a slight, beneficial afternoon respite from intense heat.
Considering the timing of planting can also optimize the benefits of companion relationships. Trap crops should be planted slightly earlier so they are established and attractive when pests first emerge. Placing companions with different root depths, such as shallow-rooted lettuce and deep-rooted tomatoes, allows each plant to access water and nutrients from different soil layers, minimizing underground competition. This arrangement creates a layered defense system that supports the tomato throughout its growing season.