When to Start Broccoli and Cabbage Seeds Indoors
On this page
Broccoli is a cool-season crop. The University of Idaho Extension guide says cool-season crops like broccoli can be transplanted outside 2 to 5 weeks before the average date of last frost. Find your date with the frost date tool.
What the source says
| Broccoli, cauliflower | Cabbage, kale, collards | |
|---|---|---|
| Ideal soil temperature for germination | 65 to 75 °F | 65 to 75 °F |
| Days to germination | 5 to 10 | 5 to 10 |
| Weeks to grow indoors | 5 to 7 | 5 to 7 |
| Move outdoors | 2 to 5 weeks before the average last frost | not stated in the guide |
The guide's sentence about moving cool-season crops outside names broccoli, onions and pansies as examples. It does not name cabbage, kale or collards. They share broccoli's seed and indoor figures, so this page works out dates for broccoli and cauliflower, and for cabbage, kale and collards it gives only the weeks indoors. Check your seed packet for their outdoor timing.
The math for broccoli and cauliflower
- Move-out window = last frost − 5 weeks to last frost − 2 weeks.
- Earliest start = earliest move-out date − 7 weeks.
- Latest start = latest move-out date − 5 weeks.
Three stations, same rules
All dates use NOAA's 50% last freeze at 32 °F and a 2027 calendar.
| Weather station | Average last freeze (50%) | Move broccoli outdoors | Start seeds indoors |
|---|---|---|---|
| Dallas-Fort Worth AP, Texas | Mar 8 | Feb 1 to Feb 22 | Dec 14 (2026) to Jan 18 |
| Port Columbus Intl AP, Ohio | Apr 18 | Mar 14 to Apr 4 | Jan 24 to Feb 28 |
| Denver Intl AP, CO | May 5 | Mar 31 to Apr 21 | Feb 10 to Mar 17 |
Check one row: Columbus, April 18 − 5 weeks = March 14, − 2 weeks = April 4. March 14 − 7 weeks = January 24. April 4 − 5 weeks = February 28.
These dates are the guide's rule applied to the average last freeze. A freeze can still follow a move-out 5 weeks before the last frost, so the seedlings will meet cold nights outdoors. That is what "cool-season" means in the guide, but the guide also notes that seedlings need hardening off, which usually takes at least a week, and protection from weather extremes once they are planted.
Sources
- University of Idaho Extension, Start Seeds Indoors with Success (CIS 1209).
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, stations named in the table.