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Broccoli Seed Starting Tips

Seedling Broccoli
Broccoli seedling
Broccoli seedling

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.

Broccoli 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 the 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 the 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, and peas. Herbs with a strong fragrance such as dill, sage, rosemary, basil, mint, garlic and thyme are also good companions for broccoli. The strong aroma of these herbs helps to repel pest insects that may attack broccoli.

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

Broccoli Planting Calendar

  • 8-6 weeks before the last frost in spring: start seed indoors for transplanting to the garden late.
  • 6-4 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 when the minimum soil temperature is 40°

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.

More tips at How to Grow Broccoli.

Broccoli in garden
Start broccoli seed indoors 7 to 9 weeks before setting out in the garden.

Broccoli 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.

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

Comments

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  1. Do you have any information on planting purple sprouting broccoli for overwintering in Zone 6? I’m looking for best varieties, planting/transplant time and winter protection. We’re usually above 10F but I can add extra coverings for the odd cold snap. It would be in a raised bed surrounded by concrete pavers with a southern exposure, full sun, if that matters. I don’t have the room for the shorter season spring-to-fall plantings, plus having fresh veg in the ‘hungry gap’ sounds wonderful to me.
    Thank you so much. You’ve helped me in the past and I’ve been able to extend my growing season and produce more veg with succession planting based on your advice.

    • Mature purple-sprouting broccoli plants can tolerate temperatures as low as 11°F (-12°C). Sow purple-sprouting broccoli in early spring to harvest in early winter, or sow from mid-spring to late-spring to harvest from mid-winter to late spring. If plants are not mature when very cold weather comes, pull a row cover over the crop. Most row covers will provide 2 to 5 degrees protection. Varieties you may want to plant include Purple Peacock, Purple Sprouting, Early Purple Sprouting, and Burgundy Hybrid.

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