Brussels sprouts are a long-season, heavy-feeding vegetable belonging to the Brassica family, sharing ancestry with cabbage and kale. Companion planting involves strategically placing different plant species near each other to create a mutually beneficial micro-ecosystem. This technique leverages natural plant interactions to support the sprouts, often resulting in healthier growth, enhanced flavor, and a reduced need for chemical interventions. Selecting appropriate neighbors addresses the Brussels sprout’s main vulnerabilities: high nutrient demands and susceptibility to insect pests. The right plant pairings offer natural solutions for defense and nourishment.
Companion Plants for Pest Management
Brussels sprouts are highly susceptible to specific pests, including the cabbage looper, imported cabbageworm, and flea beetles. Companion planting utilizes aromatic herbs and flowers to mask the attractive scent or to act as a decoy, diverting pests away from the main crop. The strong, pungent scent of herbs like rosemary is effective at confusing adult cabbage moths and butterflies, preventing them from laying their eggs on the sprout leaves. This olfactory disruption makes the Brussels sprout plants harder for the pests to locate.
Other plants serve a defensive role by attracting the beneficial insects that naturally prey on common sprout pests. Dill, for instance, produces umbel-shaped flowers that are highly attractive to parasitic wasps, such as the Cotesia glomerata, which lay their eggs inside the destructive cabbage worm larvae. These beneficial wasps effectively provide a biological control mechanism, helping to keep caterpillar populations below a damaging threshold.
Marigolds, especially the French varieties (Tagetes patula), offer defense both above and below the soil line. These flowers emit a chemical compound from their roots which is known to repel certain types of plant-damaging nematodes. Above ground, the marigold’s strong fragrance can help deter various insects and has been shown to reduce aphid colonies in some intercropping studies.
Nasturtiums function primarily as a trap crop, drawing aphids and cabbage white butterflies to their foliage. When planted nearby, the pests will preferentially feed on the nasturtiums, which are typically more appealing to them than the brassica leaves. Gardeners can then monitor the trap crop and manage the concentrated pest population, allowing the Brussels sprouts to grow unmolested.
Companions That Enhance Soil and Growth
Plants can also be selected to improve the overall growing conditions for Brussels sprouts. Legumes, such as bush beans and peas, are highly beneficial because of their symbiotic relationship with Rhizobia bacteria, which live in nodules on the plant roots. These bacteria perform a process called nitrogen fixation, converting atmospheric nitrogen gas (N2) into ammonium (NH4), a form that is readily usable by the sprouts. Since Brussels sprouts are heavy feeders, requiring a high amount of nitrogen for robust leaf and sprout development, this natural nutrient boost is especially valuable.
Bush bean varieties are often preferred over pole beans because they do not compete with the tall sprouts for vertical space or sunlight. This allows the two plants to efficiently occupy different layers of the garden bed. The nitrogen fixed by the bush beans is gradually released into the soil, slowly feeding the Brussels sprouts throughout their long growing season.
Low-growing ground covers like creeping thyme and chamomile enhance the soil environment by acting as a living mulch. Creeping thyme spreads out to form a dense mat that blocks sunlight, suppressing weed seed germination. This minimizes competition for water and nutrients, which is crucial for the sprouts’ health.
Chamomile offers similar ground cover benefits and is believed to have mild antibacterial properties that support neighboring plants. Intercropping with fast-maturing, shallow-rooted plants like lettuce maximizes space efficiency. Lettuce can be planted in the wide gaps between young Brussels sprouts and harvested quickly, often in 4 to 6 weeks, before the sprouts compete for resources.
Plants That Harm Brussels Sprouts
Certain species should be kept away from Brussels sprouts because they introduce detrimental competition or shared vulnerabilities. Planting other members of the Brassica family, such as broccoli, cabbage, or kale, is generally discouraged despite their similar needs and appearance. These related crops all attract the same major pests, including the cabbage looper and diamondback moth, which concentrates the pest population and increases the risk of a widespread infestation.
All brassicas are heavy feeders, meaning they compete aggressively with Brussels sprouts for high levels of nitrogen and other macronutrients. Planting them in close proximity can lead to nutrient depletion, resulting in stunted growth and poor sprout formation across all the competing crops. A similar problem arises with strawberries, which are also considered heavy feeders and will compete with the sprouts for moisture and soil nutrients.
Plants from the nightshade family, most notably tomatoes, should also be avoided as neighbors. More importantly, both plants are susceptible to the same soil-borne diseases, such as Verticillium wilt (Verticillium dahliae), a fungus that persists in the soil. Planting them together risks spreading this disease, which can cause wilting and eventual death in both the sprouts and the tomato plants, contaminating the soil for future plantings.