Boulder, UT frost dates
Last spring frostMay 4median date
First fall frostOct 14median date
Growing season163 daysfrost-free
Hardiness zone7aZone 7a
How Boulder compares
- In 8 years out of 10, the last spring frost in Boulder falls between April 20 and May 25, a 35-day window. The first fall frost falls between September 30 and October 29.
- The median last frost is 6 days earlier than the Utah median of May 10.
- Its 163-day growing season is longer than 67% of the 250 Utah places with a regular frost season (state median 148 days).
- The last frost is 18 days later than the zone 7a median of Apr 16. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 7a chart.
- The weather station records an average of 146 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 20 |
| 50% (median) | May 4 |
| 10% (safe for tender plants) | May 25 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 30 |
| 50% (median) | October 14 |
| 90% (late) | October 29 |
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, UT
Boulder, UT frost dates — last frost May 4, first frost Oct 14, zone 7a. whenisthelastfrost.com
Crop
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Start indoors: Feb 9 to Feb 23Transplant outside: Apr 6 to Apr 20
Start indoors: Feb 23 to Mar 9Transplant outside: May 18 to Jun 1
Start indoors: Feb 23 to Mar 9Transplant outside: May 18 to Jun 1
Start indoors: Mar 9 to Mar 23Transplant outside: May 11 to May 25
Start indoors: Mar 9 to Mar 23Transplant outside: Apr 13 to Apr 27Sow outdoors: Apr 6 to May 11Plant for fall: Aug 19 to Sep 16
Start indoors: Mar 9 to Mar 23Transplant outside: Apr 6 to Apr 20Sow outdoors: Apr 6 to Apr 20Plant for fall: Aug 5 to Aug 26
Start indoors: Mar 9 to Mar 23Transplant outside: Apr 20 to May 4Plant for fall: Jul 8 to Jul 29
Start indoors: Mar 9 to Mar 23Transplant outside: Apr 13 to Apr 27Plant for fall: Jul 8 to Jul 29
Start indoors: Mar 9 to Mar 23Transplant outside: Apr 20 to May 4Plant for fall: Jul 8 to Jul 29
Start indoors: Mar 23 to Apr 6Transplant outside: May 25 to Jun 8Sow outdoors: May 25 to Jun 8
Start indoors: Mar 23 to Apr 6Transplant outside: May 11 to May 25
Sow outdoors: Mar 23 to Apr 13Plant for fall: Jul 22 to Aug 12
Sow outdoors: Mar 23 to Apr 13Plant for fall: Aug 19 to Sep 9
Sow outdoors: Mar 30 to May 11Plant for fall: Sep 2 to Sep 23
Start indoors: Apr 6 to Apr 13Transplant outside: May 18 to May 25Sow outdoors: May 11 to May 25Plant for fall: Jul 29 to Aug 12
Start indoors: Apr 6 to Apr 13Sow outdoors: May 11 to May 25Plant for fall: Aug 5 to Aug 19
Start indoors: Apr 6 to Apr 13Sow outdoors: May 11 to May 25
Start indoors: Apr 6 to Apr 13Transplant outside: May 18 to Jun 1
Sow outdoors: Apr 13 to May 11Plant for fall: Jul 22 to Aug 5
Sow outdoors: Apr 13 to May 11Plant for fall: Aug 5 to Aug 19
Sow outdoors: Apr 13 to May 4
Sow outdoors: Apr 20 to May 18Plant for fall: Aug 5 to Aug 19
Sow outdoors: Apr 20 to May 11Plant for fall: Aug 19 to Sep 9
Sow outdoors: May 11 to Jun 1Plant for fall: Jul 29 to Aug 12
Sow outdoors: May 11 to May 25
Transplant outside: May 18 to Jun 8
Plant for fall: Sep 30 to Nov 4
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Boulder, UT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 9 – Feb 23 | Apr 6 – Apr 20 | — | — |
| Peppers | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Eggplant | Feb 23 – Mar 9 | May 18 – Jun 1 | — | — |
| Tomatoes | Mar 9 – Mar 23 | May 11 – May 25 | — | — |
| Lettuce | Mar 9 – Mar 23 | Apr 13 – Apr 27 | Apr 6 – May 11 | Aug 19 – Sep 16 |
| Kale | Mar 9 – Mar 23 | Apr 6 – Apr 20 | Apr 6 – Apr 20 | Aug 5 – Aug 26 |
| Broccoli | Mar 9 – Mar 23 | Apr 20 – May 4 | — | Jul 8 – Jul 29 |
| Cabbage | Mar 9 – Mar 23 | Apr 13 – Apr 27 | — | Jul 8 – Jul 29 |
| Cauliflower | Mar 9 – Mar 23 | Apr 20 – May 4 | — | Jul 8 – Jul 29 |
| Okra | Mar 23 – Apr 6 | May 25 – Jun 8 | May 25 – Jun 8 | — |
| Basil | Mar 23 – Apr 6 | May 11 – May 25 | — | — |
| Peas | — | — | Mar 23 – Apr 13 | Jul 22 – Aug 12 |
| Spinach | — | — | Mar 23 – Apr 13 | Aug 19 – Sep 9 |
| Radishes | — | — | Mar 30 – May 11 | Sep 2 – Sep 23 |
| Cucumbers | Apr 6 – Apr 13 | May 18 – May 25 | May 11 – May 25 | Jul 29 – Aug 12 |
| Zucchini & Summer Squash | Apr 6 – Apr 13 | — | May 11 – May 25 | Aug 5 – Aug 19 |
| Winter Squash & Pumpkins | Apr 6 – Apr 13 | — | May 11 – May 25 | — |
| Melons & Watermelon | Apr 6 – Apr 13 | May 18 – Jun 1 | — | — |
| Carrots | — | — | Apr 13 – May 11 | Jul 22 – Aug 5 |
| Beets | — | — | Apr 13 – May 11 | Aug 5 – Aug 19 |
| Potatoes | — | — | Apr 13 – May 4 | — |
| Swiss Chard | — | — | Apr 20 – May 18 | Aug 5 – Aug 19 |
| Cilantro | — | — | Apr 20 – May 11 | Aug 19 – Sep 9 |
| Green Beans | — | — | May 11 – Jun 1 | Jul 29 – Aug 12 |
| Sweet Corn | — | — | May 11 – May 25 | — |
| Sweet Potatoes | — | May 18 – Jun 8 | — | — |
| Garlic | — | — | — | Sep 30 – Nov 4 |
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, UT weather station, about 1 km away (elevation 6,650 ft (2,027 m)).
Frost dates near Boulder
- Escalante May 8 · Oct 10
- Teasdale Apr 22 · Oct 23
- Torrey Apr 22 · Oct 23
- Bicknell May 31 · Sep 21
- Antimony Jun 17 · Sep 12
- Lyman May 31 · Sep 21
- Loa May 31 · Sep 21
- Henrieville May 31 · Sep 28
- Hanksville May 5 · Oct 3
- Tropic May 23 · Sep 27
Frequently asked questions
When is the last frost in Boulder, UT?
The median last spring frost in Boulder, UT is May 4. There is still about a 10% chance of frost after May 25, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Boulder, UT?
The median first fall frost is October 14, with about a 10% chance of frost before September 30.
How long is the growing season in Boulder, UT?
About 163 days between the median last spring frost and first fall frost.
What planting zone is Boulder, UT?
Boulder, UT is in USDA hardiness zone 7a.