Broccoli Seed Starting Tips

Broccoli seedlings

Broccoli is a cool-season crop. It thrives in temperatures between 60° and 70°F (15-21°C). Mature plants can withstand cold temperatures down to 25°F (-4°).

Broccoli can be temperamental; if you plant too early plants may produce only small heads—called “buttons.” And if you plant too late—and plants mature in very warm or hot weather—heads may not form at all and plants may simply flower and go to seed.

Time spring planting so that broccoli will come to harvest before uniformly hot weather arrives. Time late spring or summer planting so that plants mature in cool autumn temperatures.

Sowing and Planting Tips:

  • Start broccoli from seed or transplants.
  • Seed is viable for 3 years.
  • For spring crop start seeds indoors 7 to 9 weeks before the average last frost date. For a fall crop, start seed indoors 10 to 12 weeks before the first fall frost.
  • Start seeds in individual pots
  • Sow seed ¼ to ½ (6-8 mm) inch deep in seed-starting mix.
  • Keep the mix moist but not wet.
  • Seeds should germinate in 5 to 10 days at an optimal temperature of 77°F (25°C) or thereabouts.
  • Transplant seedlings into the garden when they 4 to 6 inches (10-15 cm) tall with 2- to 4-leaves.
  • Grow broccoli in full sun for best yield, but broccoli will tolerate partial shade.
  • Add 3- to 4- inches of compost and well-aged manure into planting bed, before transplanting; broccoli needs friable, moisture-holding soil.
  • Avoid planting where cabbage family crops have grown recently.
  • Space plants 18 to 24 inches (45-60 cm) apart; plants spaced 10 to 12 inches (25-30 cm) apart will yield smaller heads.
  • Space rows 36 inches (.9 m) apart.
  • Protect seedlings from cold for 2 to 3 weeks after planting covering them with a cloche or plastic tunnel or cold frame.
  • Fertilize with an organic fertilizer such as fish emulsion at half strength.

Interplanting: Plant with bush beans, beets, carrots, celery, chard, cucumbers, lettuce, peas, and tomatoes.

Container Growing: Choose a container with a minimum depth of 20 inches (51 cm).

Recommended Planting Calendar:

  • 10-8 weeks before the last frost in spring: start seed indoors for transplanting to garden late.
  • 8-6 weeks before the last frost in spring: direct-sow seed in a plastic tunnel or cold frame.
  • 4-3 weeks before the last frost in spring: direct-sow seed in the garden.

For Fall and Winter Harvest:

  • 17-15 weeks before the first frost in fall: start seed of cold-tolerant varieties indoors for transplanting out at end of summer.
  • 14-12 weeks before the first frost in fall: direct sow seed of cold-tolerant varieties in garden for fall harvest.
  • 12-10 weeks before the first frost in fall: transplant seedlings into the garden.

Recommended Varieties: ‘Green Comet’ or ‘Premium Crop’ for spring planting. ‘Gypsy’ is disease resistant and matures early. ‘Arcadia’ is mid- to late-season variety with big heads and cold tolerant. ‘Belstar’ grows in warm winters. ‘Nutribud’ is open pollinated. ‘Packman’ is an early producer. ‘Small Miracle’ and ‘Munchkin’ are good for containers and small spaces. ‘Waltham 29’ is a favorite for fall harvest ‘Purple Sprouting’ has small purple heads and comes to harvest in late fall.

Botanical Name: Brassica oleracea

Broccoli is a member of the Brassicacea (Cruciferae) or cabbage family.