Companion planting is the practice of strategically growing different plants near one another to create a mutually beneficial environment. For tomato growers using a raised bed, this technique maximizes limited space and resources. Careful planning is needed, as the close proximity of plants can lead to synergistic growth or detrimental competition. The goal is to establish a small, biodiverse ecosystem where the tomato plant thrives alongside its neighbors.
Why Companion Planting Benefits Tomatoes
Companion planting relies on two primary mechanisms: pest management and soil improvement. Planting a variety of species helps disrupt the monoculture environment that often invites pest and disease outbreaks. Aromatic herbs and flowers emit strong scents that confuse or repel common tomato pests like the hornworm and whiteflies, masking the tomato’s distinctive smell. Certain plants also function as “trap crops” or attract beneficial insects, such as ladybugs and parasitic wasps, which prey on harmful garden pests.
Soil health and nutrient cycling are significantly enhanced by interplanting. Legumes, like beans, fix atmospheric nitrogen into a form plants can use, directly benefiting the nitrogen-hungry tomato plant. Low-growing companions provide a living mulch that shades the soil, conserving moisture. Their root systems also help aerate the dense raised bed soil, improving drainage.
Essential Companions: Plants That Improve Growth and Flavor
Herbs
Basil is often planted directly next to the tomato stem. Its strong aroma deters pests like whiteflies and thrips. Chives, a member of the allium family, release sulfur compounds that deter aphids, spider mites, and nematodes when planted around the perimeter. Mint can repel flea beetles and aphids with its intense scent, but it must be grown in a separate container or confined root barrier to prevent aggressive spreading. Parsley is helpful because, when allowed to flower, it attracts beneficial insects like ladybugs and parasitic wasps, which control aphid and hornworm populations.
Flowers
Marigolds are effective when planted densely around the tomatoes. Their roots release a chemical that suppresses root-knot nematodes, microscopic worms that damage tomato roots and stunt growth. Nasturtiums serve as an excellent trap crop, luring aphids away from the tomato foliage, and they also repel squash bugs and whiteflies. Borage is a bushy annual flower that attracts pollinators, which helps with fruit set, and deters tomato hornworms.
Understory and Root Crops
Low-growing vegetables like lettuce and spinach are ideal for planting beneath the tomato canopy. They act as a living ground cover, providing shade to the soil and suppressing weeds. Their short harvest window means they are removed before competing heavily with the maturing tomato. Carrots and radishes are good root-crop companions because their deep, narrow taproots help loosen the soil without competing for the same surface nutrients as the tomato’s fibrous root system. Radishes can be planted densely to break up the soil and are harvested quickly, making space for the tomato to expand.
Poor Pairings: Plants to Keep Away From Tomatoes
Certain plants should be avoided in the tomato raised bed because they hinder growth or increase the risk of disease. Members of the Brassica family, such as broccoli, cabbage, and cauliflower, are poor companions. These heavy feeders compete intensely with tomatoes for the high levels of nitrogen and nutrients needed in a raised bed.
Corn should also be avoided because it shares a common pest, the corn earworm (tomato fruitworm). Planting them together creates a larger, more attractive host environment for this damaging insect. Fennel is allelopathic, releasing chemical compounds that inhibit the growth of nearly all neighboring plants, including tomatoes.
Potatoes are susceptible to the same diseases as tomatoes, such as early and late blight. Planting them in close proximity greatly increases the chance of these fungal diseases spreading. Cucumbers require large amounts of water and increase humidity around the tomato foliage, raising the risk of fungal issues.
Raised Bed Layout and Spacing Considerations
The limited volume of a raised bed necessitates intensive planting combined with vertical support. For indeterminate tomato varieties, trellising or caging is required to direct growth upward, allowing for closer spacing of 1.5 to 2 feet between plants. Supported plants take up less horizontal space and ensure better air circulation, preventing fungal diseases in a dense environment.
Intensive planting methods, such as square-foot gardening, allow smaller, ground-level companions to be placed closer to the tomato stem, maximizing the bed’s surface area. Low-growing crops should be situated to receive enough light without being overshadowed by the mature tomato canopy, often placed a few inches away from the main stem.
Crop rotation is a necessary strategy, even in a small raised bed, to prevent disease organisms and pest populations from building up year after year. Rotating companion plants annually helps break disease cycles and ensures the soil is not consistently depleted of the same nutrients. For beds deeper than 12 inches, root crops can be planted strategically to utilize the lower soil profile, improving the overall yield per square foot.