Simms, MT frost dates
Last spring frostJun 2median date
First fall frostSep 10median date
Growing season100 daysfrost-free
Hardiness zone4bZone 4b
How Simms compares
- In 8 years out of 10, the last spring frost in Simms falls between May 18 and June 21, a 34-day window. The first fall frost falls between August 25 and September 25.
- The median last frost is 14 days later than the Montana median of May 19.
- Its 100-day growing season is longer than 11% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 25 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 170 nights a year at or below 32°F.
- Compared with Great Falls, MT, 46 km away, the last frost here is 27 days later than there and the growing season is 48 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 18 |
| 50% (median) | June 2 |
| 10% (safe for tender plants) | June 21 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | August 25 |
| 50% (median) | September 10 |
| 90% (late) | September 25 |
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 Simms, MT
Simms, MT frost dates — last frost Jun 2, first frost Sep 10, zone 4b. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Mar 10 to Mar 24Transplant outside: May 5 to May 19
Start indoors: Mar 24 to Apr 7Transplant outside: Jun 16 to Jun 30
Start indoors: Mar 24 to Apr 7Transplant outside: Jun 16 to Jun 30
Start indoors: Apr 7 to Apr 21Transplant outside: Jun 9 to Jun 23
Start indoors: Apr 7 to Apr 21Transplant outside: May 12 to May 26Sow outdoors: May 5 to Jun 9Plant for fall: Jul 16 to Aug 13
Start indoors: Apr 7 to Apr 21Transplant outside: May 5 to May 19Sow outdoors: May 5 to May 19Plant for fall: Jul 2 to Jul 23
Start indoors: Apr 7 to Apr 21Transplant outside: May 19 to Jun 2
Start indoors: Apr 7 to Apr 21Transplant outside: May 12 to May 26
Start indoors: Apr 7 to Apr 21Transplant outside: May 19 to Jun 2
Start indoors: Apr 21 to May 5Transplant outside: Jun 23 to Jul 7Sow outdoors: Jun 23 to Jul 7
Start indoors: Apr 21 to May 5Transplant outside: Jun 9 to Jun 23
Sow outdoors: Apr 21 to May 12Plant for fall: Jun 18 to Jul 9
Sow outdoors: Apr 21 to May 12Plant for fall: Jul 16 to Aug 6
Sow outdoors: Apr 28 to Jun 9Plant for fall: Jul 30 to Aug 20
Start indoors: May 5 to May 12Transplant outside: Jun 16 to Jun 23Sow outdoors: Jun 9 to Jun 23
Start indoors: May 5 to May 12Sow outdoors: Jun 9 to Jun 23
Start indoors: May 5 to May 12Sow outdoors: Jun 9 to Jun 23
Start indoors: May 5 to May 12Transplant outside: Jun 16 to Jun 30
Sow outdoors: May 12 to Jun 9
Sow outdoors: May 12 to Jun 9Plant for fall: Jul 2 to Jul 16
Sow outdoors: May 12 to Jun 2
Sow outdoors: May 19 to Jun 16Plant for fall: Jul 2 to Jul 16
Sow outdoors: May 19 to Jun 9Plant for fall: Jul 16 to Aug 6
Sow outdoors: Jun 9 to Jun 30
Sow outdoors: Jun 9 to Jun 23
Transplant outside: Jun 16 to Jul 7
Plant for fall: Aug 27 to Oct 1
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Simms, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Mar 10 – Mar 24 | May 5 – May 19 | — | — |
| Peppers | Mar 24 – Apr 7 | Jun 16 – Jun 30 | — | — |
| Eggplant | Mar 24 – Apr 7 | Jun 16 – Jun 30 | — | — |
| Tomatoes | Apr 7 – Apr 21 | Jun 9 – Jun 23 | — | — |
| Lettuce | Apr 7 – Apr 21 | May 12 – May 26 | May 5 – Jun 9 | Jul 16 – Aug 13 |
| Kale | Apr 7 – Apr 21 | May 5 – May 19 | May 5 – May 19 | Jul 2 – Jul 23 |
| Broccoli | Apr 7 – Apr 21 | May 19 – Jun 2 | — | — |
| Cabbage | Apr 7 – Apr 21 | May 12 – May 26 | — | — |
| Cauliflower | Apr 7 – Apr 21 | May 19 – Jun 2 | — | — |
| Okra | Apr 21 – May 5 | Jun 23 – Jul 7 | Jun 23 – Jul 7 | — |
| Basil | Apr 21 – May 5 | Jun 9 – Jun 23 | — | — |
| Peas | — | — | Apr 21 – May 12 | Jun 18 – Jul 9 |
| Spinach | — | — | Apr 21 – May 12 | Jul 16 – Aug 6 |
| Radishes | — | — | Apr 28 – Jun 9 | Jul 30 – Aug 20 |
| Cucumbers | May 5 – May 12 | Jun 16 – Jun 23 | Jun 9 – Jun 23 | — |
| Zucchini & Summer Squash | May 5 – May 12 | — | Jun 9 – Jun 23 | — |
| Winter Squash & Pumpkins Warning: Your frost-free season is about 100 days, which is tight for winter squash & pumpkins (100+ days). Choose early varieties and use transplants or row covers. | May 5 – May 12 | — | Jun 9 – Jun 23 | — |
| Melons & Watermelon | May 5 – May 12 | Jun 16 – Jun 30 | — | — |
| Carrots | — | — | May 12 – Jun 9 | — |
| Beets | — | — | May 12 – Jun 9 | Jul 2 – Jul 16 |
| Potatoes | — | — | May 12 – Jun 2 | — |
| Swiss Chard | — | — | May 19 – Jun 16 | Jul 2 – Jul 16 |
| Cilantro | — | — | May 19 – Jun 9 | Jul 16 – Aug 6 |
| Green Beans | — | — | Jun 9 – Jun 30 | — |
| Sweet Corn | — | — | Jun 9 – Jun 23 | — |
| Sweet Potatoes Warning: Your frost-free season is about 100 days, which is tight for sweet potatoes (100+ days). Choose early varieties and use transplants or row covers. | — | Jun 16 – Jul 7 | — | — |
| Garlic | — | — | — | Aug 27 – Oct 1 |
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 Sun Rvr 4 S, MT weather station, 11 km away (elevation 3,599 ft (1,097 m)).
Frost dates near Simms
- Fort Shaw Jun 2 · Sep 10
- Sun River Jun 2 · Sep 10
- Fairfield May 13 · Sep 27
- Power May 13 · Sep 27
- Vaughn Jun 2 · Sep 10
- Cascade May 21 · Sep 19
- Ulm May 21 · Sep 19
- Augusta May 19 · Sep 21
- Dutton May 20 · Sep 22
- Malmstrom Afb May 6 · Oct 1
Frequently asked questions
When is the last frost in Simms, MT?
The median last spring frost in Simms, MT is June 2. There is still about a 10% chance of frost after June 21, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Simms, MT?
The median first fall frost is September 10, with about a 10% chance of frost before August 25.
How long is the growing season in Simms, MT?
About 100 days between the median last spring frost and first fall frost.
What planting zone is Simms, MT?
Simms, MT is in USDA hardiness zone 4b.