Circle, MT frost dates
Last spring frostMay 17median date
First fall frostSep 22median date
Growing season128 daysfrost-free
Hardiness zone4aZone 4a
How Circle compares
- In 8 years out of 10, the last spring frost in Circle falls between May 4 and May 31, a 27-day window. The first fall frost falls between September 7 and October 6.
- The median last frost is 2 days earlier than the Montana median of May 19.
- Its 128-day growing season is longer than 55% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 5 days later than the zone 4a median of May 12. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 4a chart.
- The weather station records an average of 183 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 4 |
| 50% (median) | May 17 |
| 10% (safe for tender plants) | May 31 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 7 |
| 50% (median) | September 22 |
| 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 Circle, MT
Circle, MT frost dates — last frost May 17, first frost Sep 22, zone 4a. whenisthelastfrost.com
Crop
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Start indoors: Feb 22 to Mar 8Transplant outside: Apr 19 to May 3
Start indoors: Mar 8 to Mar 22Transplant outside: May 31 to Jun 14
Start indoors: Mar 8 to Mar 22Transplant outside: May 31 to Jun 14
Start indoors: Mar 22 to Apr 5Transplant outside: May 24 to Jun 7
Start indoors: Mar 22 to Apr 5Transplant outside: Apr 26 to May 10Sow outdoors: Apr 19 to May 24Plant for fall: Jul 28 to Aug 25
Start indoors: Mar 22 to Apr 5Transplant outside: Apr 19 to May 3Sow outdoors: Apr 19 to May 3Plant for fall: Jul 14 to Aug 4
Start indoors: Mar 22 to Apr 5Transplant outside: May 3 to May 17Plant for fall: Jun 16 to Jul 7
Start indoors: Mar 22 to Apr 5Transplant outside: Apr 26 to May 10Plant for fall: Jun 16 to Jul 7
Start indoors: Mar 22 to Apr 5Transplant outside: May 3 to May 17Plant for fall: Jun 16 to Jul 7
Start indoors: Apr 5 to Apr 19Transplant outside: Jun 7 to Jun 21Sow outdoors: Jun 7 to Jun 21
Start indoors: Apr 5 to Apr 19Transplant outside: May 24 to Jun 7
Sow outdoors: Apr 5 to Apr 26Plant for fall: Jun 30 to Jul 21
Sow outdoors: Apr 5 to Apr 26Plant for fall: Jul 28 to Aug 18
Sow outdoors: Apr 12 to May 24Plant for fall: Aug 11 to Sep 1
Start indoors: Apr 19 to Apr 26Transplant outside: May 31 to Jun 7Sow outdoors: May 24 to Jun 7Plant for fall: Jul 7 to Jul 21
Start indoors: Apr 19 to Apr 26Sow outdoors: May 24 to Jun 7Plant for fall: Jul 14 to Jul 28
Start indoors: Apr 19 to Apr 26Sow outdoors: May 24 to Jun 7
Start indoors: Apr 19 to Apr 26Transplant outside: May 31 to Jun 14
Sow outdoors: Apr 26 to May 24Plant for fall: Jun 30 to Jul 14
Sow outdoors: Apr 26 to May 24Plant for fall: Jul 14 to Jul 28
Sow outdoors: Apr 26 to May 17
Sow outdoors: May 3 to May 31Plant for fall: Jul 14 to Jul 28
Sow outdoors: May 3 to May 24Plant for fall: Jul 28 to Aug 18
Sow outdoors: May 24 to Jun 14Plant for fall: Jul 7 to Jul 21
Sow outdoors: May 24 to Jun 7
Transplant outside: May 31 to Jun 21
Plant for fall: Sep 8 to Oct 13
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Circle, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 22 – Mar 8 | Apr 19 – May 3 | — | — |
| Peppers | Mar 8 – Mar 22 | May 31 – Jun 14 | — | — |
| Eggplant | Mar 8 – Mar 22 | May 31 – Jun 14 | — | — |
| Tomatoes | Mar 22 – Apr 5 | May 24 – Jun 7 | — | — |
| Lettuce | Mar 22 – Apr 5 | Apr 26 – May 10 | Apr 19 – May 24 | Jul 28 – Aug 25 |
| Kale | Mar 22 – Apr 5 | Apr 19 – May 3 | Apr 19 – May 3 | Jul 14 – Aug 4 |
| Broccoli | Mar 22 – Apr 5 | May 3 – May 17 | — | Jun 16 – Jul 7 |
| Cabbage | Mar 22 – Apr 5 | Apr 26 – May 10 | — | Jun 16 – Jul 7 |
| Cauliflower | Mar 22 – Apr 5 | May 3 – May 17 | — | Jun 16 – Jul 7 |
| Okra | Apr 5 – Apr 19 | Jun 7 – Jun 21 | Jun 7 – Jun 21 | — |
| Basil | Apr 5 – Apr 19 | May 24 – Jun 7 | — | — |
| Peas | — | — | Apr 5 – Apr 26 | Jun 30 – Jul 21 |
| Spinach | — | — | Apr 5 – Apr 26 | Jul 28 – Aug 18 |
| Radishes | — | — | Apr 12 – May 24 | Aug 11 – Sep 1 |
| Cucumbers | Apr 19 – Apr 26 | May 31 – Jun 7 | May 24 – Jun 7 | Jul 7 – Jul 21 |
| Zucchini & Summer Squash | Apr 19 – Apr 26 | — | May 24 – Jun 7 | Jul 14 – Jul 28 |
| Winter Squash & Pumpkins | Apr 19 – Apr 26 | — | May 24 – Jun 7 | — |
| Melons & Watermelon | Apr 19 – Apr 26 | May 31 – Jun 14 | — | — |
| Carrots | — | — | Apr 26 – May 24 | Jun 30 – Jul 14 |
| Beets | — | — | Apr 26 – May 24 | Jul 14 – Jul 28 |
| Potatoes | — | — | Apr 26 – May 17 | — |
| Swiss Chard | — | — | May 3 – May 31 | Jul 14 – Jul 28 |
| Cilantro | — | — | May 3 – May 24 | Jul 28 – Aug 18 |
| Green Beans | — | — | May 24 – Jun 14 | Jul 7 – Jul 21 |
| Sweet Corn | — | — | May 24 – Jun 7 | — |
| Sweet Potatoes | — | May 31 – Jun 21 | — | — |
| Garlic | — | — | — | Sep 8 – Oct 13 |
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 Circle, MT weather station, 2 km away (elevation 2,480 ft (756 m)).
Frost dates near Circle
- Brockway May 20 · Sep 19
- Lindsay May 26 · Sep 17
- Vida May 16 · Sep 22
- Bloomfield May 3 · Oct 4
- Richey May 16 · Sep 22
- Terry May 12 · Sep 28
- Cohagen May 25 · Sep 14
- Glendive May 3 · Oct 4
- Wolf Point May 8 · Sep 28
- Fallon May 20 · Sep 22
Frequently asked questions
When is the last frost in Circle, MT?
The median last spring frost in Circle, MT is May 17. There is still about a 10% chance of frost after May 31, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Circle, MT?
The median first fall frost is September 22, with about a 10% chance of frost before September 7.
How long is the growing season in Circle, MT?
About 128 days between the median last spring frost and first fall frost.
What planting zone is Circle, MT?
Circle, MT is in USDA hardiness zone 4a.