Frost dates for 80305 — Boulder, CO
Last spring frostMay 6median date
First fall frostOct 5median date
Growing season152 daysfrost-free
Hardiness zone6aZone 6a
How Boulder compares
- In 8 years out of 10, the last spring frost in Boulder falls between April 24 and May 18, a 24-day window. The first fall frost falls between September 21 and October 18.
- The median last frost is 5 days earlier than the Colorado median of May 11.
- Its 152-day growing season is longer than 59% of the 374 Colorado places with a regular frost season (state median 146 days).
- The last frost is 7 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 138 nights a year at or below 32°F.
- Compared with Arvada, CO, 22 km away, the last frost here is 1 day later than there and the growing season is 1 day shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 24 |
| 50% (median) | May 6 |
| 10% (safe for tender plants) | May 18 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 21 |
| 50% (median) | October 5 |
| 90% (late) | October 18 |
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 80305 — Boulder, CO — last frost May 6, first frost Oct 5, zone 6a. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Feb 11 to Feb 25Transplant outside: Apr 8 to Apr 22
Start indoors: Feb 25 to Mar 11Transplant outside: May 20 to Jun 3
Start indoors: Feb 25 to Mar 11Transplant outside: May 20 to Jun 3
Start indoors: Mar 11 to Mar 25Transplant outside: May 13 to May 27
Start indoors: Mar 11 to Mar 25Transplant outside: Apr 15 to Apr 29Sow outdoors: Apr 8 to May 13Plant for fall: Aug 10 to Sep 7
Start indoors: Mar 11 to Mar 25Transplant outside: Apr 8 to Apr 22Sow outdoors: Apr 8 to Apr 22Plant for fall: Jul 27 to Aug 17
Start indoors: Mar 11 to Mar 25Transplant outside: Apr 22 to May 6Plant for fall: Jun 29 to Jul 20
Start indoors: Mar 11 to Mar 25Transplant outside: Apr 15 to Apr 29Plant for fall: Jun 29 to Jul 20
Start indoors: Mar 11 to Mar 25Transplant outside: Apr 22 to May 6Plant for fall: Jun 29 to Jul 20
Start indoors: Mar 25 to Apr 8Transplant outside: May 27 to Jun 10Sow outdoors: May 27 to Jun 10
Start indoors: Mar 25 to Apr 8Transplant outside: May 13 to May 27
Sow outdoors: Mar 25 to Apr 15Plant for fall: Jul 13 to Aug 3
Sow outdoors: Mar 25 to Apr 15Plant for fall: Aug 10 to Aug 31
Sow outdoors: Apr 1 to May 13Plant for fall: Aug 24 to Sep 14
Start indoors: Apr 8 to Apr 15Transplant outside: May 20 to May 27Sow outdoors: May 13 to May 27Plant for fall: Jul 20 to Aug 3
Start indoors: Apr 8 to Apr 15Sow outdoors: May 13 to May 27Plant for fall: Jul 27 to Aug 10
Start indoors: Apr 8 to Apr 15Sow outdoors: May 13 to May 27
Start indoors: Apr 8 to Apr 15Transplant outside: May 20 to Jun 3
Sow outdoors: Apr 15 to May 13Plant for fall: Jul 13 to Jul 27
Sow outdoors: Apr 15 to May 13Plant for fall: Jul 27 to Aug 10
Sow outdoors: Apr 15 to May 6
Sow outdoors: Apr 22 to May 20Plant for fall: Jul 27 to Aug 10
Sow outdoors: Apr 22 to May 13Plant for fall: Aug 10 to Aug 31
Sow outdoors: May 13 to Jun 3Plant for fall: Jul 20 to Aug 3
Sow outdoors: May 13 to May 27
Transplant outside: May 20 to Jun 10
Plant for fall: Sep 21 to Oct 26
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Boulder, CO
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 11 – Feb 25 | Apr 8 – Apr 22 | — | — |
| Peppers | Feb 25 – Mar 11 | May 20 – Jun 3 | — | — |
| Eggplant | Feb 25 – Mar 11 | May 20 – Jun 3 | — | — |
| Tomatoes | Mar 11 – Mar 25 | May 13 – May 27 | — | — |
| Lettuce | Mar 11 – Mar 25 | Apr 15 – Apr 29 | Apr 8 – May 13 | Aug 10 – Sep 7 |
| Kale | Mar 11 – Mar 25 | Apr 8 – Apr 22 | Apr 8 – Apr 22 | Jul 27 – Aug 17 |
| Broccoli | Mar 11 – Mar 25 | Apr 22 – May 6 | — | Jun 29 – Jul 20 |
| Cabbage | Mar 11 – Mar 25 | Apr 15 – Apr 29 | — | Jun 29 – Jul 20 |
| Cauliflower | Mar 11 – Mar 25 | Apr 22 – May 6 | — | Jun 29 – Jul 20 |
| Okra | Mar 25 – Apr 8 | May 27 – Jun 10 | May 27 – Jun 10 | — |
| Basil | Mar 25 – Apr 8 | May 13 – May 27 | — | — |
| Peas | — | — | Mar 25 – Apr 15 | Jul 13 – Aug 3 |
| Spinach | — | — | Mar 25 – Apr 15 | Aug 10 – Aug 31 |
| Radishes | — | — | Apr 1 – May 13 | Aug 24 – Sep 14 |
| Cucumbers | Apr 8 – Apr 15 | May 20 – May 27 | May 13 – May 27 | Jul 20 – Aug 3 |
| Zucchini & Summer Squash | Apr 8 – Apr 15 | — | May 13 – May 27 | Jul 27 – Aug 10 |
| Winter Squash & Pumpkins | Apr 8 – Apr 15 | — | May 13 – May 27 | — |
| Melons & Watermelon | Apr 8 – Apr 15 | May 20 – Jun 3 | — | — |
| Carrots | — | — | Apr 15 – May 13 | Jul 13 – Jul 27 |
| Beets | — | — | Apr 15 – May 13 | Jul 27 – Aug 10 |
| Potatoes | — | — | Apr 15 – May 6 | — |
| Swiss Chard | — | — | Apr 22 – May 20 | Jul 27 – Aug 10 |
| Cilantro | — | — | Apr 22 – May 13 | Aug 10 – Aug 31 |
| Green Beans | — | — | May 13 – Jun 3 | Jul 20 – Aug 3 |
| Sweet Corn | — | — | May 13 – May 27 | — |
| Sweet Potatoes | — | May 20 – Jun 10 | — | — |
| Garlic | — | — | — | Sep 21 – Oct 26 |
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 Boulder, CO weather station, 2 km away (elevation 5,486 ft (1,672 m)).
ZIP codes in Boulder: 80301 80302 80303 80304 80305 80306 80307 80308 80309 80310 80314
Frost dates near Boulder
- Eldorado Springs May 24 · Sep 23
- Louisville May 6 · Oct 5
- Lafayette May 2 · Oct 11
- Niwot May 7 · Oct 5
- Pinecliffe Jun 5 · Sep 16
- Broomfield May 2 · Oct 11
- Erie May 7 · Oct 5
- Jamestown Jun 21 · Sep 2
Frequently asked questions
When is the last frost in Boulder, CO?
The median last spring frost in Boulder, CO is May 6. There is still about a 10% chance of frost after May 18, 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 October 5, with about a 10% chance of frost before September 21.
How long is the growing season in Boulder, CO?
About 152 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.