Brussels sprouts require a long growing period, though newer hybrids have greatly reduced this requirement. In all but the most northern states, summers are usually too warm for completely satisfactory production from spring plantings. Plants set out in late spring to early summer grow satisfactorily and mature high-quality sprouts when the fall weather begins to cool. Transplant in early summer to midsummer about the same time that you would plant late, long-season cabbage. For summer harvest, you must plant transplants of an early, heat-resistant variety in very early spring.
Sprouts maturing in hot weather or under dry conditions are more likely to develop bitterness.
Fall production is the most practical and rewarding in most parts of the country. Space plants 24 to 36 inches apart in the row, or 24 inches in all directions in beds. Do not allow transplants to become stunted in the flats before transplanting. Brussels sprouts are grown much like the related cole crops, cabbage and broccoli. Apply one side-dress application of nitrogen fertilizer when the plants are 12 inches tall and water to keep the crop growing vigorously during the heat of summer.