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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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    • Scarafication in botany is the process by which the hard coating of a seed is weakened so that the seed can absorb water more quickly and hasten germination. Common natural ways for seed coats to be weakened are mechanical injury–such as scratching, chemical injury–when the seed is exposed, for example, to the acid in the gut of an animal who has eaten the seed, and thermal injury–commonly exposure to warm water. Short freezing may weaken the seed coat, but it also risks freezing and rupturing and injuring cells inside the seed. That said, many seeds germinate more quickly when exposed to warm and cold–similar to but not a freeze and thaw–usually temperatures in the mid 30s and 40sF, that is above freezing; these include cool-weather crops such as lettuce, spinach, and onions.

    • Choose the coolest time of the year to grow broccoli at the equator. Broccoli grows best at temperatures between 55 and 70F. Above 75F, broccoli will flower and go to seed.

  1. I planted seeds 10 days ago. My sprouts are tall and very thin. Some are tipping over. Should I cut them back or will they eventually strengthen up?

    • If your broccoli sprouts are indoors be sure that you are not overwatering, keep the light two inches above the plants as they grow, place a fan nearby so that there is a gentle breeze–this will help the stems grow strong and stout. If the plants are outdoors, make sure they are protected from cold nights and direct wind; place a plastic tunnel over the plants or cover them with a floating row cover.

    • You are likely in USDA Zone 7 or 8; check at a local nursery to be certain. The best time to plant broccoli will be late summer for a harvest in late autumn or early winter. In your region, the weather is now warming and broccoli will not reach maturity without flowering. Time your harvest to the cool time of the year.

  2. I’ve planted broccoli (and cauliflower seeds) and they both germinated and the broccolis really sprung up in the last week but the last two days they have begun to fall over and the cauliflower has totally disappeared. I am growing indoors under a sun-facing window so it may be too hot, but I’m not sure. Any ideas or advice?

    • Broccoli flowers when temperatures are too warm; that is the way of Nature. Plant again in late summer so that broccoli matures in the cool of autumn.

  3. I’m in zone 5a and I’m new to vegetable gardening. We bought 200 broccoli seeds awhile ago but we haven’t planted any of them yet. We now have prepared raised beds available to plant some of them, but I think they will just bolt and go to flower, due to the hot summer ahead. We aren’t set-up to really plant any indoors, although we could possibly try that with a few seeds. Will the seeds be OK to keep until next year, and we’ll try to direct seed them in early spring? Or, if we direct seed some of them outdoors, if we mulch well and water frequently with cold water (and cover them somehow, on hot days), do you think we can prevent them from bolting?

    • Look at weather/temperature history for your area to get an estimate of the average first frost date in autumn. Look at the number of days to maturity for the seeds you have; count backwards from the first frost date, add a week to 10 days, then sow some of your seeds outdoors on that date. If all goes well, you will harvest just before or about the date of the first frost–broccoli likes cool weather. You can also start some of the seeds indoors for transplanting out and save some seeds for next spring.

  4. I started growing brocolli in india in winter which has 27 degrees of temperatures but in 10 days slender seedling is weakened dont know y ?

    • Your broccoli would prefer cooler temperatures. Avoid heavy nitrogen in the soil. If the seedlings are indoors, place a fan nearby to circulate the air; this will help the stems grow stout.

  5. 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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