Frost dates for 80308 — Boulder, CO
Last spring frostMay 24median date
First fall frostSep 23median date
Growing season122 daysfrost-free
Hardiness zone6aZone 6a
How Boulder compares
- In 8 years out of 10, the last spring frost in Boulder falls between May 11 and June 10, a 30-day window. The first fall frost falls between September 9 and October 6.
- The median last frost is 13 days later than the Colorado median of May 11.
- Its 122-day growing season is longer than 29% of the 374 Colorado places with a regular frost season (state median 146 days).
- The last frost is 25 days later than the zone 6a median of Apr 29. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 6a chart.
- The weather station records an average of 188 nights a year at or below 32°F.
- Compared with Arvada, CO, 33 km away, the last frost here is 19 days later than there and the growing season is 31 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 11 |
| 50% (median) | May 24 |
| 10% (safe for tender plants) | June 10 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 9 |
| 50% (median) | September 23 |
| 90% (late) | October 6 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Boulder, CO
Frost dates for 80308 — Boulder, CO — last frost May 24, first frost Sep 23, zone 6a. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Mar 1 to Mar 15Transplant outside: Apr 26 to May 10
Start indoors: Mar 15 to Mar 29Transplant outside: Jun 7 to Jun 21
Start indoors: Mar 15 to Mar 29Transplant outside: Jun 7 to Jun 21
Start indoors: Mar 29 to Apr 12Transplant outside: May 31 to Jun 14
Start indoors: Mar 29 to Apr 12Transplant outside: May 3 to May 17Sow outdoors: Apr 26 to May 31Plant for fall: Jul 29 to Aug 26
Start indoors: Mar 29 to Apr 12Transplant outside: Apr 26 to May 10Sow outdoors: Apr 26 to May 10Plant for fall: Jul 15 to Aug 5
Start indoors: Mar 29 to Apr 12Transplant outside: May 10 to May 24Plant for fall: Jun 17 to Jul 8
Start indoors: Mar 29 to Apr 12Transplant outside: May 3 to May 17Plant for fall: Jun 17 to Jul 8
Start indoors: Mar 29 to Apr 12Transplant outside: May 10 to May 24Plant for fall: Jun 17 to Jul 8
Start indoors: Apr 12 to Apr 26Transplant outside: Jun 14 to Jun 28Sow outdoors: Jun 14 to Jun 28
Start indoors: Apr 12 to Apr 26Transplant outside: May 31 to Jun 14
Sow outdoors: Apr 12 to May 3Plant for fall: Jul 1 to Jul 22
Sow outdoors: Apr 12 to May 3Plant for fall: Jul 29 to Aug 19
Sow outdoors: Apr 19 to May 31Plant for fall: Aug 12 to Sep 2
Start indoors: Apr 26 to May 3Transplant outside: Jun 7 to Jun 14Sow outdoors: May 31 to Jun 14Plant for fall: Jul 8 to Jul 22
Start indoors: Apr 26 to May 3Sow outdoors: May 31 to Jun 14Plant for fall: Jul 15 to Jul 29
Start indoors: Apr 26 to May 3Sow outdoors: May 31 to Jun 14
Start indoors: Apr 26 to May 3Transplant outside: Jun 7 to Jun 21
Sow outdoors: May 3 to May 31Plant for fall: Jul 1 to Jul 15
Sow outdoors: May 3 to May 31Plant for fall: Jul 15 to Jul 29
Sow outdoors: May 3 to May 24
Sow outdoors: May 10 to Jun 7Plant for fall: Jul 15 to Jul 29
Sow outdoors: May 10 to May 31Plant for fall: Jul 29 to Aug 19
Sow outdoors: May 31 to Jun 21Plant for fall: Jul 8 to Jul 22
Sow outdoors: May 31 to Jun 14
Transplant outside: Jun 7 to Jun 28
Plant for fall: Sep 9 to Oct 14
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Boulder, CO
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Mar 1 – Mar 15 | Apr 26 – May 10 | — | — |
| Peppers | Mar 15 – Mar 29 | Jun 7 – Jun 21 | — | — |
| Eggplant | Mar 15 – Mar 29 | Jun 7 – Jun 21 | — | — |
| Tomatoes | Mar 29 – Apr 12 | May 31 – Jun 14 | — | — |
| Lettuce | Mar 29 – Apr 12 | May 3 – May 17 | Apr 26 – May 31 | Jul 29 – Aug 26 |
| Kale | Mar 29 – Apr 12 | Apr 26 – May 10 | Apr 26 – May 10 | Jul 15 – Aug 5 |
| Broccoli | Mar 29 – Apr 12 | May 10 – May 24 | — | Jun 17 – Jul 8 |
| Cabbage | Mar 29 – Apr 12 | May 3 – May 17 | — | Jun 17 – Jul 8 |
| Cauliflower | Mar 29 – Apr 12 | May 10 – May 24 | — | Jun 17 – Jul 8 |
| Okra | Apr 12 – Apr 26 | Jun 14 – Jun 28 | Jun 14 – Jun 28 | — |
| Basil | Apr 12 – Apr 26 | May 31 – Jun 14 | — | — |
| Peas | — | — | Apr 12 – May 3 | Jul 1 – Jul 22 |
| Spinach | — | — | Apr 12 – May 3 | Jul 29 – Aug 19 |
| Radishes | — | — | Apr 19 – May 31 | Aug 12 – Sep 2 |
| Cucumbers | Apr 26 – May 3 | Jun 7 – Jun 14 | May 31 – Jun 14 | Jul 8 – Jul 22 |
| Zucchini & Summer Squash | Apr 26 – May 3 | — | May 31 – Jun 14 | Jul 15 – Jul 29 |
| Winter Squash & Pumpkins | Apr 26 – May 3 | — | May 31 – Jun 14 | — |
| Melons & Watermelon | Apr 26 – May 3 | Jun 7 – Jun 21 | — | — |
| Carrots | — | — | May 3 – May 31 | Jul 1 – Jul 15 |
| Beets | — | — | May 3 – May 31 | Jul 15 – Jul 29 |
| Potatoes | — | — | May 3 – May 24 | — |
| Swiss Chard | — | — | May 10 – Jun 7 | Jul 15 – Jul 29 |
| Cilantro | — | — | May 10 – May 31 | Jul 29 – Aug 19 |
| Green Beans | — | — | May 31 – Jun 21 | Jul 8 – Jul 22 |
| Sweet Corn | — | — | May 31 – Jun 14 | — |
| Sweet Potatoes | — | Jun 7 – Jun 28 | — | — |
| Garlic | — | — | — | Sep 9 – Oct 14 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Gross Rsvr, CO weather station, 11 km away (elevation 7,969 ft (2,429 m)).
ZIP codes in Boulder: 80301 80302 80303 80304 80305 80306 80307 80308 80309 80310 80314
Frost dates near Boulder
- Jamestown Jun 21 · Sep 2
- Nederland Jun 21 · Sep 2
- Pinecliffe Jun 5 · Sep 16
- Ward Jun 21 · Sep 2
- Eldorado Springs May 24 · Sep 23
- Rollinsville Jun 5 · Sep 16
- Niwot May 7 · Oct 5
- Louisville May 6 · Oct 5
Frequently asked questions
When is the last frost in Boulder, CO?
The median last spring frost in Boulder, CO is May 24. There is still about a 10% chance of frost after June 10, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Boulder, CO?
The median first fall frost is September 23, with about a 10% chance of frost before September 9.
How long is the growing season in Boulder, CO?
About 122 days between the median last spring frost and first fall frost.
What planting zone is Boulder, CO?
Boulder, CO is in USDA hardiness zone 6a.