Bok choy, an Asian cabbage, is a fast-growing, cool-season crop prized for its tender leaves and crisp stalks. Like many leafy greens, it is susceptible to various garden pests and can bolt, or prematurely flower, if stressed by heat. Companion planting involves placing certain species near bok choy to enhance growth, provide natural pest deterrence, and create a more resilient and productive growing space.
Companion Plants for Pest Control and Vigor
Aromatic herbs and flowers are effective partners for bok choy by confusing common garden pests. The strong scent of plants like dill, thyme, and mint can mask the brassica odor, making it difficult for cabbage moths to locate host plants. Dill, in particular, attracts beneficial insects, such as predatory wasps and ladybugs, that prey on destructive pests like aphids and cabbage worms.
Planting alliums, such as garlic or chives, provides a chemical defense. The sulfur compounds released by alliums repel aphids, flea beetles, and cabbage worms, which are major threats to young bok choy. Marigolds are another protective companion, as certain varieties release chemicals from their roots that suppress soil-dwelling nematodes. This helps create a healthier underground environment for the bok choy’s shallow root system, promoting robust initial growth.
Nasturtiums offer a dual benefit, acting as a physical barrier and a trap crop. They draw aphids and caterpillars away from the bok choy leaves, luring pests to themselves instead. Chamomile is also a supportive neighbor because it attracts hoverflies and other minute predators that feed on smaller insects, helping to manage localized pest outbreaks.
Plants for Mutual Benefit and Soil Health
Pairing bok choy with legumes, such as bush beans or peas, enriches the soil naturally. Legumes convert atmospheric nitrogen into a usable form through nitrogen fixation. Since bok choy is a heavy feeder requiring abundant nitrogen for leafy growth, this partnership provides a continuous nutrient supply, promoting faster development and larger leaves.
Other excellent companions have contrasting root structures that minimize competition for surface nutrients and water. Lettuce and spinach, for example, have shallow root systems that occupy a different soil layer than bok choy, allowing both crops to thrive in close proximity. This interplanting optimizes garden space. The dense leaf canopy of these low-growing companions also helps to shade the soil, keeping the root zone cool and moist.
For summer plantings, when the risk of bolting is highest, bok choy benefits from the partial shade of taller crops. Placing bok choy near established plants like corn or sunflowers shields it from intense midday sun. This shading reduces heat stress, the primary trigger for premature flowering in cool-season brassicas, extending the harvest window.
Incompatible Neighbors to Avoid
Certain plants should be kept separate from bok choy because they work against its success through resource competition or shared vulnerabilities. The most important group to avoid are other members of the Brassica family, including cabbage, broccoli, kale, and cauliflower. These relatives share a common susceptibility to pests like the cabbage worm and flea beetle, creating a concentrated target for infestation.
Brassica relatives are also heavy feeders, leading to intense competition for nitrogen and potassium. When planted together, both crops often suffer from nutrient deficiencies and stunted growth. Similarly, aggressive, deep-feeding crops like tomatoes are poor neighbors for bok choy, as they aggressively deplete the soil of nitrogen and potassium, leaving little for the shallow-rooted bok choy.
Certain plants release chemicals that inhibit the growth of nearby species, a phenomenon called allelopathy. Sunflowers, for instance, release compounds that suppress the development of bok choy seedlings, making them unsuitable companions. Strawberries should also be avoided because their dense, aggressive root systems compete directly with bok choy for surface-level water and nutrients.