Companion planting involves placing specific crops near one another to provide mutual benefits. Broccoli, a member of the Brassica family, is a heavy feeder requiring abundant nutrients and is highly susceptible to common garden pests. By selecting the right companions, gardeners can establish a cooperative micro-ecosystem that naturally manages pests and optimizes resource distribution. This approach is designed to reduce stress on the broccoli plant, leading to a healthier, more productive yield.
Plants That Offer Protection and Support
Many plants offer natural defenses for broccoli. Aromatic herbs are particularly effective, as their strong odors disrupt the chemical signals pests like the cabbage moth use to locate their host plants. Herbs such as rosemary, dill, and thyme emit volatile compounds that effectively repel the imported cabbageworm and the cabbage looper, which are common threats to all brassicas.
Certain flowers and herbs attract beneficial predators that naturally control pest populations. Dill, for example, attracts parasitic wasps and ladybugs, which are highly effective against aphids and other small, soft-bodied insects. Nasturtiums are often used as a “trap crop,” drawing aphids and flea beetles away from the broccoli. Their sprawling growth habit also provides a secondary benefit by shading the soil.
Low-growing vegetables can provide crucial support for broccoli’s shallow root system by acting as a living mulch. Leafy greens like lettuce and spinach thrive in the partial shade provided by the taller broccoli canopy. This interplanting keeps the soil cool and moist around the broccoli’s roots, which helps prevent the plant from bolting prematurely. Root vegetables such as beets and radishes are excellent companions because they occupy a different soil depth. Since these root crops utilize nutrients lower in the soil profile, they avoid direct competition with the broccoli’s surface-level feeder roots.
Plants That Compete or Hinder Growth
Gardeners must avoid planting broccoli near species that can actively hinder its growth or increase the risk of disease and pest outbreaks. Other members of the Brassica family, such as cabbage, cauliflower, or kale, should be avoided. Grouping them concentrates pests like the cabbage worm and increases pressure on the entire crop. They also compete directly for the large quantities of nitrogen and calcium that broccoli requires for head formation, leading to nutrient depletion.
Other heavy-feeding plants, including corn, squash, and sunflowers, are also poor choices for proximity to broccoli. These crops strip the soil of nutrients, leaving insufficient resources for the demanding broccoli plant. Furthermore, nightshade family members, such as tomatoes, peppers, and eggplants, should be kept at a distance due to their conflicting needs and resource competition. Tomatoes, for example, prefer a slightly acidic soil pH, while broccoli performs best in neutral to slightly alkaline soil, making them incompatible neighbors.
Some plants release chemical compounds that inhibit the growth of nearby species. Strawberries, for instance, release compounds that can stunt the development of brassicas. They are also heavy feeders with aggressive spreading habits and tend to attract pests like aphids, which can easily migrate to the vulnerable broccoli plants. Avoiding these competitive or inhibitory plants is important for a successful harvest.
Managing Soil Health and Nutrient Availability
Nitrogen is a primary requirement for the development of large, dense broccoli heads. This need can be met by planting legumes like bush beans or peas nearby. These plants host rhizobia bacteria in their root nodules, which fix atmospheric nitrogen into a form that is bioavailable in the soil. While this nitrogen is highly beneficial, it is important to avoid an overdose, which can lead to excessive leaf growth at the expense of the desired central head.
To maximize the nitrogen benefit, the legume plant should be cut at the base rather than pulled out entirely when the season ends. Leaving the roots to decompose naturally releases the stored nitrogen into the soil for the next crop cycle. Companions can also be selected to manage the physical properties of the soil, which is crucial for water retention around the shallow-rooted broccoli plant.
Low-growing companions like nasturtiums or low-cut clover serve a dual purpose as ground cover to suppress weed growth and act as a living mulch. This ground cover shades the soil surface, significantly reducing water evaporation. Deep-rooted vegetables, like beets and celery, help to aerate the soil and improve drainage in the lower layers without interfering with the broccoli’s primary feeding zone.