Broccoli is an ideal plant for raised bed gardens. It thrives in consistently moist, rich soil, doesn't require any special care or attention and is very productive.
Broccoli is a cool weather crop. For best results, the plants should reach maturity either before or after hot weather sets in. For an early summer crop, get your broccoli off to a fast start by planting seedlings rather than seeds. Start the seeds indoors under lights and put the plants into the garden about four weeks before the last spring frost. For a fall broccoli crop, young plants should be transplanted into the garden in late summer, six weeks before the first frost. You'll probably need to start your own fall broccoli plants from seed, because it's unusual to find them for sale at garden centers; you can plant the seeds directly in the ground or in small pots.
Each broccoli plant will produce one large head in the center of the plant, and then produce edible side shoots for months afterwards. The central head is ready to harvest when it looks fully formed and the buds are still tight and dark green. Flavor and quality is best when the heads are compact. If you wait too long, the buds will start to open and turn yellow, and the flavor will become bitter.
To harvest the central head, use a sharp knife and cut the stem carefully, preferably at an angle, several inches below the crown. A week or two later, the plant will begin sending up smaller heads from the sides of the center stem. If you harvest these side shoots when the buds are still tight and green, they will be just as tasty as the first full-size head. Keep harvesting several times each week and the plant will usually keep producing for several months. At the end of the season when there is little else to harvest from the garden, you can eat some of the young broccoli leaves by steaming them like cabbage or kale.
To protect broccoli seedlings from flea beetles and cabbageworm, cover the plants with row cover (garden fabric) for the first few weeks that they're in the garden. Extreme cold or heat can cause broccoli to "button" which means the central head doesn't develop properly, and instead forms a small, bitter knob. If this happens, cut off the deformed central head and in most cases the plant will still produce a good crop of side shoots.
Plant breeders have developed broccoli varieties that are specifically suited to spring or fall growing conditions. Some varieties are also better at producing side shoots than others. If you grow your own broccoli from seed, you can seek out these special varieties.