Brussels sprouts, scientifically classified as Brassica oleracea in the Gemmifera Group, are a unique member of the cabbage family. Unlike their relatives, these plants produce small, edible buds rather than a single large head. They are a cool-weather vegetable that requires a long growing season of 90 to 110 days or more to reach maturity. This prolonged period of growth is necessary for the plant to develop its tall, sturdy stalk.
Essential Environmental Needs
Brussels sprouts require consistent cool temperatures throughout their development. They thrive best when temperatures are consistently in the range of 60–65°F (15 to 18°C) and can become bitter if they mature during periods of sustained heat. Although typically grown as annuals, they require full sun exposure, ideally receiving eight to ten hours of direct light daily.
The soil must be rich in organic matter, well-drained, and maintained at a slightly alkaline pH, ideally around 6.8. These plants are heavy feeders, requiring high levels of nutrients to support the growth of their large leaves and thick central stem. Consistent moisture is necessary; inconsistent watering can stress the plant, leading to poor development and loose, subpar sprouts.
Starting and Establishing the Crop
Seeds are often sown indoors approximately four to six weeks before the last expected spring frost date. Starting seeds early helps ensure the plants are robust enough to withstand the summer heat and mature during the preferred cool weather of fall.
Transplanting typically occurs in early to mid-summer, allowing the required 90 to 110 days for a fall or early winter harvest. Plants must be spaced generously, usually 18 to 24 inches apart, to provide adequate air circulation and room for the substantial foliage to develop. Following transplanting, the young plants require a steady supply of water and nutrients, often benefiting from side-dressings of nitrogen fertilizer as they reach about a foot in height. Preventing damage from pests, particularly cabbage worms, is necessary early on to protect the leaves that power the plant’s growth.
The Development of Sprouts
The edible sprouts are tight, miniature heads that develop along the main stem. As the plant grows, it forms a tall, thick stalk, which can reach up to three feet in height, with large leaves extending outward. The sprouts emerge from the axils, which are the points where the base of each leaf meets the main stem.
These axillary buds develop in a spiral pattern, beginning their maturation at the bottom of the stalk and progressing upward over several weeks. Adequate light must reach the developing sprouts; some growers remove the lower, yellowing leaves to ensure sufficient exposure and energy for growth. To encourage all sprouts to mature at a more uniform rate for a single harvest, growers can perform “topping.” This involves removing the plant’s apical bud or growing tip late in the season, redirecting the plant’s energy away from vertical growth and toward the swelling of the existing sprouts.
Timing the Harvest
Harvest begins once the sprouts are firm, tightly closed, and have reached an optimal diameter of approximately one to one and a half inches. Because the sprouts mature sequentially from the bottom to the top, harvesting is typically a staggered process. The lower sprouts are picked first, and harvesting continues upward as the higher sprouts firm up.
To remove a sprout, a gardener can simply snap it off with a sharp downward twist or use a knife or shears for a clean cut at the stem. The flavor improves significantly after it has been exposed to one or two light frosts. This “cold sweetening” effect occurs as the plant converts starches into sugars to protect itself from freezing temperatures, resulting in a sweeter, less bitter taste.