Grass Range, MT frost dates
Last spring frostMay 20median date
First fall frostSep 24median date
Growing season127 daysfrost-free
Hardiness zone4bZone 4b
How Grass Range compares
- In 8 years out of 10, the last spring frost in Grass Range falls between May 6 and June 6, a 31-day window. The first fall frost falls between September 11 and October 5.
- The median last frost is 1 day later than the Montana median of May 19.
- Its 127-day growing season is longer than 54% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 12 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 171 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 6 |
| 50% (median) | May 20 |
| 10% (safe for tender plants) | June 6 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 11 |
| 50% (median) | September 24 |
| 90% (late) | October 5 |
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 Grass Range, MT
Grass Range, MT frost dates — last frost May 20, first frost Sep 24, zone 4b. whenisthelastfrost.com
Crop
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Start indoors: Feb 25 to Mar 11Transplant outside: Apr 22 to May 6
Start indoors: Mar 11 to Mar 25Transplant outside: Jun 3 to Jun 17
Start indoors: Mar 11 to Mar 25Transplant outside: Jun 3 to Jun 17
Start indoors: Mar 25 to Apr 8Transplant outside: May 27 to Jun 10
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 29 to May 13Sow outdoors: Apr 22 to May 27Plant for fall: Jul 30 to Aug 27
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 22 to May 6Sow outdoors: Apr 22 to May 6Plant for fall: Jul 16 to Aug 6
Start indoors: Mar 25 to Apr 8Transplant outside: May 6 to May 20Plant for fall: Jun 18 to Jul 9
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 29 to May 13Plant for fall: Jun 18 to Jul 9
Start indoors: Mar 25 to Apr 8Transplant outside: May 6 to May 20Plant for fall: Jun 18 to Jul 9
Start indoors: Apr 8 to Apr 22Transplant outside: Jun 10 to Jun 24Sow outdoors: Jun 10 to Jun 24
Start indoors: Apr 8 to Apr 22Transplant outside: May 27 to Jun 10
Sow outdoors: Apr 8 to Apr 29Plant for fall: Jul 2 to Jul 23
Sow outdoors: Apr 8 to Apr 29Plant for fall: Jul 30 to Aug 20
Sow outdoors: Apr 15 to May 27Plant for fall: Aug 13 to Sep 3
Start indoors: Apr 22 to Apr 29Transplant outside: Jun 3 to Jun 10Sow outdoors: May 27 to Jun 10Plant for fall: Jul 9 to Jul 23
Start indoors: Apr 22 to Apr 29Sow outdoors: May 27 to Jun 10Plant for fall: Jul 16 to Jul 30
Start indoors: Apr 22 to Apr 29Sow outdoors: May 27 to Jun 10
Start indoors: Apr 22 to Apr 29Transplant outside: Jun 3 to Jun 17
Sow outdoors: Apr 29 to May 27Plant for fall: Jul 2 to Jul 16
Sow outdoors: Apr 29 to May 27Plant for fall: Jul 16 to Jul 30
Sow outdoors: Apr 29 to May 20
Sow outdoors: May 6 to Jun 3Plant for fall: Jul 16 to Jul 30
Sow outdoors: May 6 to May 27Plant for fall: Jul 30 to Aug 20
Sow outdoors: May 27 to Jun 17Plant for fall: Jul 9 to Jul 23
Sow outdoors: May 27 to Jun 10
Transplant outside: Jun 3 to Jun 24
Plant for fall: Sep 10 to Oct 15
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Grass Range, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 25 – Mar 11 | Apr 22 – May 6 | — | — |
| Peppers | Mar 11 – Mar 25 | Jun 3 – Jun 17 | — | — |
| Eggplant | Mar 11 – Mar 25 | Jun 3 – Jun 17 | — | — |
| Tomatoes | Mar 25 – Apr 8 | May 27 – Jun 10 | — | — |
| Lettuce | Mar 25 – Apr 8 | Apr 29 – May 13 | Apr 22 – May 27 | Jul 30 – Aug 27 |
| Kale | Mar 25 – Apr 8 | Apr 22 – May 6 | Apr 22 – May 6 | Jul 16 – Aug 6 |
| Broccoli | Mar 25 – Apr 8 | May 6 – May 20 | — | Jun 18 – Jul 9 |
| Cabbage | Mar 25 – Apr 8 | Apr 29 – May 13 | — | Jun 18 – Jul 9 |
| Cauliflower | Mar 25 – Apr 8 | May 6 – May 20 | — | Jun 18 – Jul 9 |
| Okra | Apr 8 – Apr 22 | Jun 10 – Jun 24 | Jun 10 – Jun 24 | — |
| Basil | Apr 8 – Apr 22 | May 27 – Jun 10 | — | — |
| Peas | — | — | Apr 8 – Apr 29 | Jul 2 – Jul 23 |
| Spinach | — | — | Apr 8 – Apr 29 | Jul 30 – Aug 20 |
| Radishes | — | — | Apr 15 – May 27 | Aug 13 – Sep 3 |
| Cucumbers | Apr 22 – Apr 29 | Jun 3 – Jun 10 | May 27 – Jun 10 | Jul 9 – Jul 23 |
| Zucchini & Summer Squash | Apr 22 – Apr 29 | — | May 27 – Jun 10 | Jul 16 – Jul 30 |
| Winter Squash & Pumpkins | Apr 22 – Apr 29 | — | May 27 – Jun 10 | — |
| Melons & Watermelon | Apr 22 – Apr 29 | Jun 3 – Jun 17 | — | — |
| Carrots | — | — | Apr 29 – May 27 | Jul 2 – Jul 16 |
| Beets | — | — | Apr 29 – May 27 | Jul 16 – Jul 30 |
| Potatoes | — | — | Apr 29 – May 20 | — |
| Swiss Chard | — | — | May 6 – Jun 3 | Jul 16 – Jul 30 |
| Cilantro | — | — | May 6 – May 27 | Jul 30 – Aug 20 |
| Green Beans | — | — | May 27 – Jun 17 | Jul 9 – Jul 23 |
| Sweet Corn | — | — | May 27 – Jun 10 | — |
| Sweet Potatoes | — | Jun 3 – Jun 24 | — | — |
| Garlic | — | — | — | Sep 10 – Oct 15 |
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 Grass Range, MT weather station, 2 km away (elevation 3,491 ft (1,064 m)).
Frost dates near Grass Range
- Teigen May 20 · Sep 24
- Forest Grove May 19 · Sep 25
- Roy May 14 · Sep 24
- Winnett May 16 · Sep 28
- Lewistown May 14 · Sep 28
- Hilger May 14 · Sep 28
- Moore May 23 · Sep 21
- Roundup May 20 · Sep 21
- Winifred May 16 · Sep 23
- Judith Gap Jun 1 · Sep 15
Frequently asked questions
When is the last frost in Grass Range, MT?
The median last spring frost in Grass Range, MT is May 20. There is still about a 10% chance of frost after June 6, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Grass Range, MT?
The median first fall frost is September 24, with about a 10% chance of frost before September 11.
How long is the growing season in Grass Range, MT?
About 127 days between the median last spring frost and first fall frost.
What planting zone is Grass Range, MT?
Grass Range, MT is in USDA hardiness zone 4b.