Companion planting is an organic method of gardening that uses plants to assist each other in growing. Plants all contain various natural substances that can either aid or hinder another plant's growing abilities. Companion planting is also an important part of integrated pest management by repelling harmful insects without losing any beneficial allies. Brussels sprouts is part of the cabbage family and suffers and benefits from the same factors as other members of the cabbage family. Several herbs and crops make useful companions to Brussels sprouts.
Chamomile improves the flavor of Brussels sprouts, but use it sparingly. Only grow one plant every 150 feet because this low-growing herb with daisy-like apple-scented flowers is a creeper and can spread quickly. Garlic is another companion herb that improves the flavor of Brussels sprouts. Additionally, garlic doubles as a pest repellent and has anti-fungal properties, too. Garlic plants are easy to grow and grow from the individual cloves on the bulb. Nearby sage plants also help to make Brussels sprouts more succulent and tasty. Sage also likes to grow next to rosemary, which is a pest deterrent for cabbage crops.
Cabbage crops including Brussels sprouts are all susceptible to the same pests. Plant onions nearby to keep the hardest to control insect -- aphids -- in check. These small green, orange, yellow, red, black or white insects suck the plant's juices, causing yellow leaves. Nasturtiums also help deter aphids from Brussels sprout plants by acting as a trap that the aphids flock to. Nasturtiums also keep away various types of beetles like the flea beetle, which chew tiny holes in the Brussels sprouts leaves and roots. Another leaf-chewing pest is the cabbage worm, which is curbed by planting potatoes. Cabbage worms morph into cabbage white butterflies or moths, which also are a pest to Brussels sprout crops. Plant celery stalks to lure them away, as well as aromatic herbs like sage, hyssop, rosemary, peppermint and catnip.
Grow beets next to Brussels sprouts to help the soil's fertility. They contribute minerals to the soil like magnesium. Magnesium deficiency is a common problem when growing Brussels sprouts, and is identified by yellowish outer areas around the leaves. Beets are also a companion plant to onions, another of Brussels sprouts companions, and help deter common pests like aphids. Grow all three close to each other for maximum performance. Green manures are cover crops that are grown specifically to return nutrients back to the soil. Brussels sprouts are heavy feeders and often require a lot of nitrogen, which leguminous cover crops are big suppliers of. Alfalfa is one the highest nitrogen providers. Other useful cover crops for Brussels sprouts are clover, winter rye and vetch.
Although both plants are cool season crops, never plant Brussels sprouts, or any other member of the cabbage family, near strawberry plants. Brussels sprout plant growth is inhibited when planted near strawberries. Keep Brussels sprout plants away from tomatoes and pole beans, too. Cabbage crops contain plant chemicals that inhibit tomato growth, as well as other nightshades like eggplants and peppers.