Brussels sprouts (Brassica oleracea var. gemmifera) are cool-weather members of the cabbage family. They require a long growing season and significant nutrients to produce their characteristic miniature heads. Like other brassicas, they are susceptible to various pests and depend on nutrient-rich soil for a successful harvest. Strategic companion planting uses the synergy between different plant species to provide mutual benefits, such as defense against insects or enhancement of soil quality. Choosing the right neighbors promotes plant health and maximizes overall yields without relying on chemical interventions.
Beneficial Companions for Pest Deterrence
The distinct, sulfurous scent of Brussels sprouts attracts common garden pests like the cabbage worm, cabbage moth, and flea beetles. Planting highly aromatic herbs and alliums nearby confuses these insects by masking the sprouts’ scent. Strong-smelling herbs release volatile compounds that overwhelm the sprouts’ natural odor.
Thyme is effective at repelling the cabbage worm (the larval stage of the small white butterfly), while sage deters the cabbage moth, cabbage looper, and flea beetles. Alliums, including garlic, onions, and leeks, also protect the sprouts. Their sulfur compounds have a pungent, repellent effect on aphids, slugs, and cabbage loopers, and may also provide anti-fungal properties against soil-borne diseases.
Certain flowers provide powerful pest control by distracting or trapping insects. Nasturtiums and geraniums emit a peppery scent that repels cabbage worms and flea beetles. Nasturtiums can also serve as a trap crop, drawing aphids away from the sprouts.
Radishes, which grow quickly, can be planted nearby to act as a trap crop for flea beetles, as the pests prefer radish leaves over Brussels sprouts foliage. Planting dill is also advantageous because its flowers attract beneficial insects, such as parasitic wasps, that prey on destructive pests like cabbage loopers and aphids.
Growth-Enhancing Neighbors and Soil Health
Brussels sprouts are heavy feeders, requiring consistently high levels of soil nutrients, especially nitrogen. Legumes like bush beans and peas are excellent companions because they form a symbiotic relationship with Rhizobia bacteria in their root nodules. These bacteria perform nitrogen fixation, converting atmospheric nitrogen into a plant-usable form, naturally fertilizing the soil for the sprouts.
French marigolds (Tagetes patula) suppress harmful root-knot nematodes in the soil. These flowers release nematicidal compounds from their roots, which poison the nematodes. Incorporating French marigolds into a crop rotation or planting them nearby contributes to a healthier root environment.
Soil Structure and Mulch
Carrots, with their deep taproots, help to aerate and loosen compacted soil. This improves water penetration and root growth for the Brussels sprouts. Beets also make a good neighbor, as they use different soil layers than the sprouts and add magnesium to the soil, a nutrient beneficial for brassica development.
Low-growing herbs or leafy greens, such as oregano or lettuce, function as a living mulch. They cover the soil surface to reduce water evaporation. This also helps keep the shallow roots of the sprouts cool during warmer periods.
Plants That Must Be Avoided
Selecting the wrong companion is detrimental, often by introducing competition for resources or acting as a shared host for pests and diseases. The most important plants to avoid are other members of the brassica family:
- Cabbage
- Broccoli
- Cauliflower
- Kale
These plants are heavy feeders and compete directly with Brussels sprouts for nitrogen and other soil nutrients. Planting brassicas together creates a concentrated target for shared pests like the cabbage worm and flea beetle, increasing the risk of widespread infestation.
Competing Vegetables
Several heavy-feeding vegetables must be kept separate due to their high demand for nutrients and water. These plants aggressively compete for soil resources and can significantly stunt the growth and yield of the Brussels sprouts:
- Tomatoes
- Potatoes
- Sweetcorn
- Peppers
- Squash
Strawberries should also be avoided, as they are heavy feeders and suppress brassica growth. Their dense, low-growing foliage creates a damp environment that harbors slugs and other pests near the base of the plants. Melons and pole beans are poor choices because their extensive, sprawling root systems and vining habits compete for both water and light. This ultimately reduces the vigor and productivity of the nearby sprouts.