Cool-weather growing broccoli is a spring and fall crop in much of the United states, and grows throughout winter in milder areas. Starting indoors or planting in cold frames extends the growing season by protecting the broccoli plants from the elements. A nutritious garden vegetable, broccoli takes from 55 to 100 days to reach maturity, and warm summer temperatures will cause it to quickly enter seed production, ruining the harvest. Grow broccoli in spring in areas with a long cool spring or wait for fall if your summers warm up too quickly.
Plant seedlings outdoors four weeks before the last frost date in spring so the broccoli can take advantage of cool-season growing. Plant seeds directly in the garden in fall approximately 10 to 12 weeks before the first frost is expected.
Plant in well-drained soil. Work in organic matter, such as compost, to raise the bed 3 inches and improve drainage before planting.
Grow broccoli in full sun. Keep in mind spring trees will leaf out and may block sun to the broccoli later in the growing season, so avoid those areas.
Apply a 2- to 4-inch layer of organic mulch, such as bark or wood chips, over the broccoli bed to conserve moisture and keep the soil cool.
Water when regular rainfall is less than 1 inch per week. Keep soil moist but not soaking wet.
Fertilize with a nitrogen-rich fertilizer at mid-season. Apply the fertilizer around the plant and not directly on top of it.
Harvest the central broccoli head when it reaches 5 inches across and before it turns yellow. Harvest side shoots until the broccoli plant bolts in summer or dies off in winter.
Plant in a cold frame to protect broccoli from winter elements. Prop open the frame on warm days and close on cool days.