Brussels sprouts are cool-season vegetables that require a long growing period and significant resources to produce their characteristic miniature heads. They are known as heavy feeders, demanding high levels of soil nutrients, particularly nitrogen, throughout their development. Placing them next to an incompatible plant can lead to stunted growth and a drastically reduced harvest. Understanding these negative interactions prevents nearby plants from becoming competitors, disease vectors, or chemical inhibitors.
Plants That Compete for Essential Resources
Brussels sprouts are heavy feeders, and planting them near other crops with similar nutritional needs creates intense competition for localized soil reserves. This struggle often starves the Brussels sprouts, which are slower to establish than many common garden vegetables. Heavy feeders like tomatoes and eggplants are poor neighbors because they aggressively draw substantial nitrogen and phosphorus from the soil.
Melons and squash varieties present intense competition due to their extensive root systems and high water requirements. These sprawling plants can quickly deplete the surrounding moisture, leaving the deep-rooted Brussels sprouts dehydrated and stressed. Similarly, strawberries are also heavy feeders that compete directly for nutrients and water, often resulting in poor sprout development.
Neighbors That Attract Pests and Disease
The most significant threat comes from plants that share or attract the same pests and pathogens. Since Brussels sprouts belong to the Brassica family, planting them near other brassicas like cabbage, broccoli, cauliflower, or kale is highly discouraged. These related crops act as a biological bridge, allowing pests such as the cabbage worm, cabbage looper, and flea beetle to easily migrate and multiply.
The shared susceptibility extends to pathogens; planting Brussels sprouts near strawberries, for example, increases the risk of soil-borne diseases like Verticillium wilt. Certain aromatic herbs can also pose a biological threat by acting as a “trap crop” that lures specific insects. Dill, rosemary, and mint can attract the egg-laying Cabbage White Butterfly, whose larvae, the cabbage worms, then feed voraciously on the nearby Brussels sprout leaves. Concentrating these susceptible plants creates a high-density food source, leading to pest outbreaks.
Plants That Chemically Inhibit Growth
A less common but equally damaging interaction is allelopathy, where one plant chemically suppresses the growth of another. This effect is caused by the release of biochemicals, known as allelochemicals, into the soil or air. The herb fennel (Foeniculum vulgare) is the most prominent example of an allelopathic plant that should be kept far away from Brussels sprouts.
Fennel releases compounds through its roots and decomposing matter that can stunt the growth of most nearby vegetables, including brassicas. These chemicals interfere with the cellular processes of the neighboring plant, inhibiting germination and overall development. Brussels sprouts are highly sensitive to the potent growth-suppressing compounds released by plants such as fennel, causing them to struggle even if their water and nutrient needs are met.