The term “brassicas” refers to a large family of cool-season vegetables, often called “cole crops,” including staples like cabbage, broccoli, cauliflower, Brussels sprouts, and kale. While prized for their hardiness and nutritional value, these plants are highly susceptible to specific pests and demand a significant amount of nutrients from the soil. Companion planting involves strategically placing different plant species near one another to create a mutually supportive garden ecosystem. This age-old technique aims to foster a healthier environment for your brassicas using natural plant interactions.
The Logic of Companion Planting with Brassicas
Companion planting offers brassicas two primary benefits: defense against pests and support for their high nutritional needs. The most damaging insects, such as the cabbage moth and flea beetle, often locate their host plants using scent cues. Planting highly aromatic herbs or alliums nearby masks the distinct odor of the brassica leaves, confusing pests and disrupting their ability to lay eggs.
Brassicas are known as heavy feeders, meaning they deplete the soil of nitrogen and other minerals quickly to support their rapid leaf and head development. Companion plants can help replenish these resources or make existing nutrients more available. For instance, some legumes fix atmospheric nitrogen into the soil, while other deep-rooted plants act as “dynamic accumulators,” drawing up trace minerals from deeper soil layers to the surface where brassicas can access them. This biological interplay reduces the need for external fertilizers and promotes overall soil vitality.
Allies: Plants That Protect and Support Brassicas
Plants that offer pest deterrence are some of the most effective allies for your brassica patch. Alliums, including garlic, onions, and chives, emit strong sulfur compounds that repel common pests like the cabbage maggot and cabbage worm. Aromatic herbs such as rosemary, thyme, and sage overwhelm the garden with powerful fragrances, making it difficult for the cabbage white butterfly to locate brassica plants for egg-laying.
Attracting beneficial insects is another defense mechanism. Small, nectar-rich flowers like sweet alyssum and dill attract predatory insects such as ladybugs, lacewings, and parasitic wasps. These beneficial creatures naturally control destructive pests like aphids and cabbage worms, maintaining biological balance. Dill also offers the added benefit of potentially enhancing the growth and flavor of nearby cabbage plants.
Other companions assist in managing soil conditions and maximizing space. Legumes like bush beans and clover are excellent choices because they fix nitrogen, a nutrient brassicas consume heavily. Low-growing plants, such as loose-leaf lettuce, can be intercropped between the slower-maturing brassicas, acting as living mulch to suppress weeds and maintain soil moisture. The deep taproot of borage brings up minerals that benefit brassicas, and its flowers attract pollinators.
Adversaries: Plants to Avoid Planting Near Brassicas
Not all plants are suitable neighbors for brassicas, and two main issues necessitate avoidance: intense resource competition and shared vulnerabilities to pests and diseases. Brassicas require significant nitrogen, phosphorus, and potassium, so planting them near other heavy feeders results in detrimental competition for nutrients. Crops like sweetcorn, asparagus, potatoes, and squash are highly demanding of soil resources and should be planted separately to prevent stunted growth.
The second major concern involves shared susceptibility to specific problems. Planting brassicas too close to other members of the Brassicaceae family, such as radishes or mustards, increases the concentration of pests and diseases specific to the family, making the entire patch more vulnerable. Furthermore, nightshade family members like tomatoes and peppers are hosts for Verticillium wilt, a soil-borne fungus that can also damage brassica roots. Strawberries can attract slugs and snails that will inevitably migrate to and damage tender brassica leaves.
Practical Layout and Garden Planning
Implementing a successful companion planting strategy requires intentional planning beyond simple adjacency. Intercropping, the practice of planting different crops simultaneously, is highly effective for brassicas. This involves spacing aromatic herbs or alliums strategically throughout the brassica rows, rather than just planting them along the border, to maximize the scent-masking effect. For instance, planting one dill or chamomile plant for every few brassicas ensures their protective influence is well-distributed.
Crop rotation is fundamental, especially for brassicas, due to their heavy feeding habit and susceptibility to soil-borne diseases. You should avoid planting brassicas in the same spot for more than one season to break the pest and disease cycle. When planning the arrangement, consider the growth habit of companions; tall plants should be placed where they will not cast too much shade on the brassicas, which generally prefer full sun for robust head formation.