Brussels sprouts (Brassica oleracea var. gemmifera) are cool-season vegetables requiring a long growing period. As members of the Brassica family, they are heavy feeders and susceptible to specific pests, making them ideal for companion planting. This technique involves strategically placing different plant species near each other to create a mutually beneficial environment. Successful cultivation requires selecting companions that deter common pests or contribute necessary resources without competing for the sprouts.
Beneficial Companion Plants
Aromatic herbs serve as pest confusion agents, disrupting the ability of insects like the cabbage moth to locate the sprouts. Planting pungent herbs such as thyme, rosemary, or sage nearby masks the odor of the Brassica foliage. This chemical camouflage reduces the likelihood that adult white butterflies will lay eggs on the sprout leaves, limiting the population of cabbage worms.
Other companions improve the soil structure and nutrient profile required by Brussels sprouts. Legumes, including bush beans and clover, perform nitrogen fixation, enriching the soil with the high levels of nitrogen sprouts need for development. Deep-rooted vegetables like carrots loosen and aerate the soil. This benefits the sprouts’ shallow root system by allowing for better water and nutrient uptake.
Certain flowers and vegetables function as trap crops, drawing pests away from the main harvest. Fast-growing radishes are attractive to flea beetles, diverting these insects away from the sprout seedlings. Nasturtiums act as a preferred host for aphids and cabbage worms, concentrating the infestation on the sacrificial plant. This allows the infestation to be monitored and managed more easily.
Plants to Avoid
Placing other members of the Brassica family too close to Brussels sprouts is discouraged. Vegetables like cabbage, broccoli, and kale share the same susceptibility to pests such as the cabbage looper and flea beetle. Planting them together creates a concentrated food source. This can lead to a widespread infestation across the entire bed.
Brussels sprouts require a high quantity of nutrients, particularly nitrogen and calcium, throughout their long season. They should be kept separate from other plants with similarly high demands that would compete for limited resources. Heavy-feeding nightshades, such as tomatoes and potatoes, or sprawling crops like corn and squash, can outcompete the sprouts for water and soil nutrients. This competition results in stunted growth and a poor yield.
Specific plants can have an inhibitory effect on Brassica growth, regardless of nutrient competition. Strawberries chemically suppress the growth of all plants in the cabbage family when planted too closely. This allelopathic effect occurs because strawberries release compounds that stunt the development of the Brussels sprouts.
Strategic Placement for Pest Deterrence
The effectiveness of companion planting relies on the strategic placement of deterrents. A common method is intercropping, which involves alternating rows of Brussels sprouts with rows of quick-growing, scented herbs or leafy greens. This creates a physical and aromatic barrier that makes it difficult for pests like the cabbage moth to find and colonize the sprouts.
Aromatic plants like mint and sage are most effective when planted as a border around the entire bed, forming a protective perimeter. These scent-masking herbs must be established early in the season, before the cabbage moths begin their egg-laying cycle. Placing small, scented plants, like chamomile, directly between the sprouts also helps confuse pests by breaking up the visual and olfactory signals of the main crop.
Trap crops require a different placement strategy to maximize their function. Nasturtiums should be planted at the edges of the row, far enough away from the sprouts to draw pests, but close enough to be easily checked. Once the nasturtiums become infested with aphids or cabbage worms, the entire trap plant can be removed and discarded. This eliminates a large number of pests before they migrate to the Brussels sprouts.