Bighorn, MT frost dates
Last spring frostMay 26median date
First fall frostSep 16median date
Growing season113 daysfrost-free
Hardiness zone4bZone 4b
How Bighorn compares
- In 8 years out of 10, the last spring frost in Bighorn falls between May 12 and June 13, a 32-day window. The first fall frost falls between September 1 and October 1.
- The median last frost is 7 days later than the Montana median of May 19.
- Its 113-day growing season is longer than 25% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 18 days later than the zone 4b median of May 8. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 4b chart.
- The weather station records an average of 194 nights a year at or below 32°F.
- Compared with Billings, MT, 96 km away, the last frost here is 22 days later than there and the growing season is 43 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 12 |
| 50% (median) | May 26 |
| 10% (safe for tender plants) | June 13 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 1 |
| 50% (median) | September 16 |
| 90% (late) | October 1 |
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 Bighorn, MT
Bighorn, MT frost dates — last frost May 26, first frost Sep 16, zone 4b. whenisthelastfrost.com
Crop
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Start indoors: Mar 3 to Mar 17Transplant outside: Apr 28 to May 12
Start indoors: Mar 17 to Mar 31Transplant outside: Jun 9 to Jun 23
Start indoors: Mar 17 to Mar 31Transplant outside: Jun 9 to Jun 23
Start indoors: Mar 31 to Apr 14Transplant outside: Jun 2 to Jun 16
Start indoors: Mar 31 to Apr 14Transplant outside: May 5 to May 19Sow outdoors: Apr 28 to Jun 2Plant for fall: Jul 22 to Aug 19
Start indoors: Mar 31 to Apr 14Transplant outside: Apr 28 to May 12Sow outdoors: Apr 28 to May 12Plant for fall: Jul 8 to Jul 29
Start indoors: Mar 31 to Apr 14Transplant outside: May 12 to May 26Plant for fall: Jun 10 to Jul 1
Start indoors: Mar 31 to Apr 14Transplant outside: May 5 to May 19Plant for fall: Jun 10 to Jul 1
Start indoors: Mar 31 to Apr 14Transplant outside: May 12 to May 26Plant for fall: Jun 10 to Jul 1
Start indoors: Apr 14 to Apr 28Transplant outside: Jun 16 to Jun 30Sow outdoors: Jun 16 to Jun 30
Start indoors: Apr 14 to Apr 28Transplant outside: Jun 2 to Jun 16
Sow outdoors: Apr 14 to May 5Plant for fall: Jun 24 to Jul 15
Sow outdoors: Apr 14 to May 5Plant for fall: Jul 22 to Aug 12
Sow outdoors: Apr 21 to Jun 2Plant for fall: Aug 5 to Aug 26
Start indoors: Apr 28 to May 5Transplant outside: Jun 9 to Jun 16Sow outdoors: Jun 2 to Jun 16Plant for fall: Jul 1 to Jul 15
Start indoors: Apr 28 to May 5Sow outdoors: Jun 2 to Jun 16Plant for fall: Jul 8 to Jul 22
Start indoors: Apr 28 to May 5Sow outdoors: Jun 2 to Jun 16
Start indoors: Apr 28 to May 5Transplant outside: Jun 9 to Jun 23
Sow outdoors: May 5 to Jun 2Plant for fall: Jun 24 to Jul 8
Sow outdoors: May 5 to Jun 2Plant for fall: Jul 8 to Jul 22
Sow outdoors: May 5 to May 26
Sow outdoors: May 12 to Jun 9Plant for fall: Jul 8 to Jul 22
Sow outdoors: May 12 to Jun 2Plant for fall: Jul 22 to Aug 12
Sow outdoors: Jun 2 to Jun 23
Sow outdoors: Jun 2 to Jun 16
Transplant outside: Jun 9 to Jun 30
Plant for fall: Sep 2 to Oct 7
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Bighorn, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Mar 3 – Mar 17 | Apr 28 – May 12 | — | — |
| Peppers | Mar 17 – Mar 31 | Jun 9 – Jun 23 | — | — |
| Eggplant | Mar 17 – Mar 31 | Jun 9 – Jun 23 | — | — |
| Tomatoes | Mar 31 – Apr 14 | Jun 2 – Jun 16 | — | — |
| Lettuce | Mar 31 – Apr 14 | May 5 – May 19 | Apr 28 – Jun 2 | Jul 22 – Aug 19 |
| Kale | Mar 31 – Apr 14 | Apr 28 – May 12 | Apr 28 – May 12 | Jul 8 – Jul 29 |
| Broccoli | Mar 31 – Apr 14 | May 12 – May 26 | — | Jun 10 – Jul 1 |
| Cabbage | Mar 31 – Apr 14 | May 5 – May 19 | — | Jun 10 – Jul 1 |
| Cauliflower | Mar 31 – Apr 14 | May 12 – May 26 | — | Jun 10 – Jul 1 |
| Okra | Apr 14 – Apr 28 | Jun 16 – Jun 30 | Jun 16 – Jun 30 | — |
| Basil | Apr 14 – Apr 28 | Jun 2 – Jun 16 | — | — |
| Peas | — | — | Apr 14 – May 5 | Jun 24 – Jul 15 |
| Spinach | — | — | Apr 14 – May 5 | Jul 22 – Aug 12 |
| Radishes | — | — | Apr 21 – Jun 2 | Aug 5 – Aug 26 |
| Cucumbers | Apr 28 – May 5 | Jun 9 – Jun 16 | Jun 2 – Jun 16 | Jul 1 – Jul 15 |
| Zucchini & Summer Squash | Apr 28 – May 5 | — | Jun 2 – Jun 16 | Jul 8 – Jul 22 |
| Winter Squash & Pumpkins Warning: Your frost-free season is about 113 days, which is tight for winter squash & pumpkins (100+ days). Choose early varieties and use transplants or row covers. | Apr 28 – May 5 | — | Jun 2 – Jun 16 | — |
| Melons & Watermelon | Apr 28 – May 5 | Jun 9 – Jun 23 | — | — |
| Carrots | — | — | May 5 – Jun 2 | Jun 24 – Jul 8 |
| Beets | — | — | May 5 – Jun 2 | Jul 8 – Jul 22 |
| Potatoes | — | — | May 5 – May 26 | — |
| Swiss Chard | — | — | May 12 – Jun 9 | Jul 8 – Jul 22 |
| Cilantro | — | — | May 12 – Jun 2 | Jul 22 – Aug 12 |
| Green Beans | — | — | Jun 2 – Jun 23 | — |
| Sweet Corn | — | — | Jun 2 – Jun 16 | — |
| Sweet Potatoes Warning: Your frost-free season is about 113 days, which is tight for sweet potatoes (100+ days). Choose early varieties and use transplants or row covers. | — | Jun 9 – Jun 30 | — | — |
| Garlic | — | — | — | Sep 2 – Oct 7 |
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 Hysham 25 Sse, MT weather station, 15 km away (elevation 3,100 ft (945 m)).
Frost dates near Bighorn
- Custer May 22 · Sep 22
- Hysham May 10 · Sep 29
- Hardin May 13 · Sep 29
- Sanders May 10 · Sep 29
- Crow Agency May 13 · Sep 29
- Pompeys Pillar May 22 · Sep 22
- Colstrip May 15 · Sep 30
- Garryowen May 13 · Sep 29
- Forsyth May 9 · Sep 29
- Busby May 23 · Sep 15
Frequently asked questions
When is the last frost in Bighorn, MT?
The median last spring frost in Bighorn, MT is May 26. There is still about a 10% chance of frost after June 13, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Bighorn, MT?
The median first fall frost is September 16, with about a 10% chance of frost before September 1.
How long is the growing season in Bighorn, MT?
About 113 days between the median last spring frost and first fall frost.
What planting zone is Bighorn, MT?
Bighorn, MT is in USDA hardiness zone 4b.