Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Consumer trends show an increase in consumption of Brussels sprouts, offering potential market opportunities for Delaware growers. Brussels sprouts have been grown successfully on a commercial level in Delaware in past years. Most East Coast production currently is centered on Long Island in New York.
Brussels sprouts were developed in maritime Europe, hence the name, and are best adapted to coastal Delmarva areas due to the more moderate temperatures. Further inland, production can be more challenging because they are very stress susceptible.
Brussels sprouts are in the cole crop group (Brassica olearacea var. gemmifer) and are closely related to cabbage, cauliflower, broccoli, kohlrabi, collards, and kale. Brussels sprouts require a long growing season and are best grown as a summer planted and fall harvested crop in Delaware. Sprouts that are produced during hot periods will be bitter, therefore spring planting is not recommended.
Recommended varieties for our region include Dimitri (105 days) and Dagan (100 days). Varieties for trial include Silvia (103 days), Marte (103 days), and Capitola (late)
Brussels sprouts can be grown as transplants in 72-128 cell flats or can be field seeded in transplant beds for bare root transplants. Transplants should be started in May or early June and then field transplanted from the third week in June to the second week in July. Long season varieties should be planted by the end of June. Use shorter maturing varieties for later plantings. Brussels sprouts are transplanted in the field at a spacing of 36″ between rows and 15-24″ in the row. Double rows on white plastic mulch with drip irrigation is an option.
Brussels sprouts require 100-150 lbs/A of nitrogen split with 50-75 lbs/A at planting and the remainder as side-dressings or fertigations. Apply 25-40 lbs/A of sulfur with nitrogen preplant applications and include 1.5-3.0 lbs/A of boron per acre and 0.2 lbs/A of molybdenum per acre as micronutrients.
Irrigation is required, with particular attention needed in summer months to achieve the equivalent of 2 inches of water per week during July and August. The goal with Brussels sprouts is to promote rapid early growth, limiting stress in the summer, and then to reduce nutrients and irrigation in September to promote sprout development.
Herbicides for weed control in Brussels sprouts are limited compared to other cole crops. Broadleaf weed control will be limited and cultivation or hand hoeing may be necessary. Brussels sprouts may be planted on white plastic mulch with drip irrigation for weed management. Do not use black plastic mulch because it is too hot.
Insect pests are similar to other cole crops and include caterpillars (imported cabbage worm, diamondback moth, cabbage looper, armyworms), aphids, thrips, and harlequin bug. Diseases include black rot, Alternaria leaf spot, and downy mildew.
The sprouts that are harvested are buds that grow to resemble miniature cabbage heads. They are produced in leaf axils along the main stem, which can grow up to 4 feet in height. Remove leaves on the lower part of the stem as the sprouts enlarge. Some growers’ top plants to promote sprout maturation but we have found that not to be necessary
Figure 1. Brussels sprouts in late December.
Sprouts for local sales can be harvested at a diameter of ¾ inch, whereas sprouts for wholesale markets should be allowed to get about 1½ inch in diameter before harvesting. Sprouts are cut or snapped off of the stem and are often directly harvested into pint or quart containers or bags. Potential harvest period for our region is the end of September through November or a heavy freeze. Sales into December are possible, especially with supplemental row covers. Brussels sprouts are very cold tolerant (hardy down to 20°F) and flavor will improve (they will be less bitter) in the colder part of the harvest season. Yields will be 2-3 lbs/plant.
An alternative method of harvest is to cut entire stems once the majority of sprouts have sized, remove the leaves, and sell as sprouts on the stalk. This is a popular method for roadside stands and other direct markets and requires much less labor.
Brussels sprouts can be room cooled, forced air cooled, hydrocooled, vacuum cooled, or top iced. They should be brought to a temperature of 32-34°F and kept at high humidity (90-95%) for storage or transportation and benefit from top icing. Brussels sprouts have a relatively long shelf of 3-5 weeks if properly stored.