Broccoli is a winter-hardy vegetable of the cabbage family known for its vitamin A and D content. Most varieties yield over an extended period and can be planted in early spring and again in the fall for two crops a year, extending the season almost year round. Broccoli is fast growing and can usually be harvested within three to four months of planting.
There are two slightly different vegetables known as broccoli. Calabrese forms a large green head. Sprouting broccoli grows many small florets instead of a single head.
Choose a sunny site, sheltered from the wind, with fertile, well-drained soil. Test the pH of the soil and add lime if needed to increase the pH to at least 6.8. Broccoli will grow in lower pH soil, but a pH of at least 6.8 will protect against clubroot.
Apply a base dressing of general-purpose fertilizer before planting sprouting broccoli. Supplement with boron, magnesium and calcium while the plants are young.
Plant broccoli seeds in mid-spring through early summer, about 1/2 to 3/4 inch deep. Plant in groups of 2 or 3 seeds positioned about 12 inches apart in rows at least 12 to 18 inches apart. Sprouting broccoli needs more room; plant it 24 inches apart in all directions. Plant seeds in succession so they don't all mature at once.
Water the plants well and frequently during the summer. The plants will need less water as the weather cools and will do better in the winter with less water. Apply a mulch of garden compost during the growing season to conserve moisture. Remove weeds as they appear.
Thin the seedlings, leaving the strongest plant in each group and removing the others.
Protect the young plants from pecking by birds, if needed, using a row cover of netting or screening over the plants. Plants that are not sheltered from the wind may need staking as they mature.
Watch for pests. Holes in the leaves or head might indicate an infestation of cabbage worms or loopers. Inspect plants daily and pick off any worms or loopers you find. Check for aphids on the undersides of leaves. Aphids can be controlled by washing with soapy water.
Harvest calabrese broccoli when main head is 4 to 6 inches in diameter and flower buds are developed but closed. After the main head is cut, the plant will develop side shoots. Harvest side shoots when 1 to 2 inches in diameter.
Harvest sprouting broccoli regularly to encourage the plant to produce more buds. With good management, sprouting broccoli will continue to produce for up to two months.
Rotate crops to prevent clubroot. Move broccoli plants yearly so they are not planted where broccoli or other members of the cabbage family have been recently planted.