Broccoli needs cool weather to grow–warm weather will cause the buds to “rice” or open as flowers.
Broccoli is suited for springs that are long and cool or autumns where there is no Indian summer. Where winters are mild, start broccoli in fall for harvest in spring.
Planting Calendar. Broccoli is a cool-season vegetable that requires from 40 to 90 days to reach harvest depending upon the variety. Broccoli grows best in temperatures that range from no more than 80ºF (27ºC) during the day to about 60°F at night. Broccoli is frost hardy and can tolerate temperatures as low as 20ºF. Temperatures that are too cold or too warm will cause broccoli to bolt without forming a head. Plant broccoli so that it comes to harvest during cool weather.
• Spring crop. Sow broccoli seed 4 to 6 weeks before your region’s average last frost date for a late spring harvest.
• Autumn and winter crop. For a fall or winter harvest, transplant broccoli seedlings into the garden in midsummer in the North. In mild winter regions such as the South and Southwest, broccoli can be planted in the fall. In cold regions, broccoli should come to maturity before the freezing weather sets in; protect broccoli in a plastic tunnel for harvest into winter.
Place. Broccoli grows best in full sun, but will grow in light shade. Broccoli is not a suitable crop for very hot climates.
Soil. Broccoli prefers rich, well-drained soil with a neutral pH within the 6.5 to 7.5 range. Work plenty of compost into the soil at planting time.
Spacing. Sow broccoli seed ½ inch deep and 3 inches apart. When seedlings are big enough to lift by their true leaves, about 4 to 6 weeks old, thin seedlings to 18 to 24 inches apart in wide beds or blocks. Rows should be spaced 24 to 36 inches apart. Thinned seedlings can be transplanted to another part of the garden. Transplants that are leggy or have crooked stems can be planted up to their first leaves so that won’t grow to be top heavy.
Container growing. Broccoli can be grown in a container 8 inches deep. Set plants at least 18 inches apart in large containers. Containers can warm quickly and broccoli is sensitive to heat so move containers into the shade on very warm days. Broccoli grown in containers is more easily protected from cold in the early spring;set out earlier in spring that transplants into the garden.
Water. Broccoli should be well watered from the outset. Keep soil moist but not wet. Cut back on watering as the heads approach maturity and harvest.
Feed. Work plenty of compost into the planting bed at planting time and then side dress broccoli plants with compost at midseason. Avoid high nitrogen fertilizers which can make stems hollow.
Suggested varieties. Green Comet (40 days); Packman (56 days); Premium Crop (60 days); Green Valiant (60 days); Top Star (60 days); Prominence (62 days); Royal Purple Head (90 days).
More tips at How to Grow Broccoli.