When to start broccoli seeds
Short answer: start broccoli indoors 4 to 6 weeks before transplanting, and transplant 2 to 4 weeks before your average last frost. It is a cool-season crop, so timing is about beating summer heat, not waiting for it.
At a glance
- Start indoors
- 4–6 weeks before setting out (UNH; Iowa State)
- Set out
- 2–4 weeks before last frost (UNH)
- Germination temperature
- 65–70°F (Iowa State); no bottom heat needed (UMN)
- Days to sprout
- 4–7 days at 65–70°F (Iowa State); UMN says about two weeks at room temperature
- Direct sow?
- Yes, for a fall crop (UMN direct seeds in July in Minnesota)
UNH = University of New Hampshire Extension; UMN = University of Minnesota Extension; Harrington = J. F. Harrington's germination data as published by Oregon State University Extension. Full links are under Sources below.
Your dates: broccoli seed-starting calculator
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How many weeks before the last frost?
University of New Hampshire Extension gives broccoli 4 to 6 weeks from seed to transplant and says it is safe to set out 2 to 4 weeks before the last frost. That means seeds go in roughly 6 to 10 weeks before your last frost date. With an average last frost of May 10, you would sow indoors March 1 to March 15 and set plants out April 12 to April 26.
Why so early? Broccoli is a cool-season crop that tolerates light frost. Planting it early lets heads form before hot weather. In Minnesota, UMN suggests starting spring broccoli indoors in early to mid-April.
Germination
Broccoli germinates readily. Iowa State Extension lists 65–70°F with seedlings in 4 to 7 days. UC Master Gardener materials give a 40°F minimum and a 60–85°F optimum range for soil. UMN specifically says not to use bottom heat: seeds germinate and grow well at ordinary room temperature, and UMN's guide says to expect seedlings in about two weeks. The difference between those two estimates is mostly temperature, so a warmer room gives faster emergence.
Press seeds a quarter to a half inch deep in sterile seedling mix (UMN). Turn on bright lights as soon as seedlings emerge.
Growing on
UMN suggests fertilizing with a half-strength starter solution once a week when the first true leaf appears, increasing to twice a week after two true leaves. When plants have four or five true leaves, after about four weeks, they are ready to harden off.
Hardening off and transplanting
Reduce watering and put plants outside where they get wind protection and a couple of hours of sun, then give them more sun and wind over the next week. Keep them well watered. UMN spaces broccoli 8 to 10 inches apart, setting plants at the same level they grew in the pot, and suggests a row cover for the first weeks to block wind and insects. Anchor the edges firmly; a loose cover flapping in wind can do more damage than no cover.
Fall broccoli and direct sowing
Broccoli is often better in fall, when heads mature in cool weather. UMN starts fall broccoli in early to late July, either indoors or by direct seeding: drop three seeds every 8 to 10 inches, a quarter to a half inch deep, then thin to one. Keep summer seedlings watered; heat, wind and insects hit hardest when plants are small. To work out the latest sowing date for your area, use the fall planting calculator.
Common mistakes
- Planting out too late. If spring broccoli matures in hot weather, heads are often small or loose. Go out 2–4 weeks before last frost.
- Using a heat mat. Brassica seedlings grow tall and weak when warm. Room temperature is enough.
- Old, root-bound transplants. Aim to transplant at four to five true leaves.
- Skipping row cover. Young plants are vulnerable to wind, cold and insects.
Example schedules
The same timing rules applied to three different average last frost dates. Find your own date on the frost dates page, or check your zone planting calendar for typical ranges.
| Last frost | Start indoors | Plant out | Direct sow |
|---|---|---|---|
| Mar 15 | Jan 4–Jan 18 | Feb 15–Mar 1 | — |
| Apr 15 | Feb 4–Feb 18 | Mar 18–Apr 1 | — |
| May 15 | Mar 6–Mar 20 | Apr 17–May 1 | — |
Supplies
Optional. You can start seeds with very little gear; these are the items that make the steps above easier. Disclosure: some links on this site may be affiliate links; if you buy through them we may earn a commission at no extra cost to you. Learn more.
- Floating row cover and wire hoops: UMN recommends covers for wind, cold and insects in the first weeks.
- Cell trays and seed-starting mix: broccoli only needs 4–6 weeks indoors, so small cells work.
- Broccoli seed (spring and fall varieties): look for days to maturity that fit before summer heat or fall frost.
Frequently asked questions
How early can I plant broccoli outside?
UNH Extension says broccoli is safe to set out 2 to 4 weeks before your average last frost, after hardening off.
Does broccoli need a heat mat to germinate?
No. UMN advises against bottom heat; seeds germinate at room temperature. Iowa State lists 65–70°F with emergence in 4–7 days.
When should I start broccoli for a fall harvest?
UMN starts fall broccoli in early to late July in Minnesota. Elsewhere, count back from your first fall frost with the fall planting calculator.
Sources
- University of New Hampshire Extension — Growing Vegetables: When to Plant Your Vegetable Garden
- Iowa State University Extension — Germination Requirements for Annuals and Vegetables
- UC Master Gardeners (Sacramento County) — Garden Notes 154: Soil temperature conditions for vegetable seed germination (PDF)
- University of Minnesota Extension — Growing broccoli in home gardens
- University of Minnesota Extension — Starting seeds indoors
Dates in the calculator and example tables use the University of New Hampshire Extension timings. Average frost dates are not guarantees; check the forecast before setting out tender plants. Last reviewed 2026-10-23. Found an error? Tell us.