Sweet Grass, MT frost dates
Last spring frostMay 15median date
First fall frostSep 25median date
Growing season133 daysfrost-free
Hardiness zone4aZone 4a
How Sweet Grass compares
- In 8 years out of 10, the last spring frost in Sweet Grass falls between May 3 and May 28, a 25-day window. The first fall frost falls between September 11 and October 8.
- The median last frost is 4 days earlier than the Montana median of May 19.
- Its 133-day growing season is longer than 66% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is typical for zone 4a, where the median is May 12.
- The weather station records an average of 179 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 3 |
| 50% (median) | May 15 |
| 10% (safe for tender plants) | May 28 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 11 |
| 50% (median) | September 25 |
| 90% (late) | October 8 |
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 Sweet Grass, MT
Sweet Grass, MT frost dates — last frost May 15, first frost Sep 25, zone 4a. whenisthelastfrost.com
Crop
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Start indoors: Feb 20 to Mar 6Transplant outside: Apr 17 to May 1
Start indoors: Mar 6 to Mar 20Transplant outside: May 29 to Jun 12
Start indoors: Mar 6 to Mar 20Transplant outside: May 29 to Jun 12
Start indoors: Mar 20 to Apr 3Transplant outside: May 22 to Jun 5
Start indoors: Mar 20 to Apr 3Transplant outside: Apr 24 to May 8Sow outdoors: Apr 17 to May 22Plant for fall: Jul 31 to Aug 28
Start indoors: Mar 20 to Apr 3Transplant outside: Apr 17 to May 1Sow outdoors: Apr 17 to May 1Plant for fall: Jul 17 to Aug 7
Start indoors: Mar 20 to Apr 3Transplant outside: May 1 to May 15Plant for fall: Jun 19 to Jul 10
Start indoors: Mar 20 to Apr 3Transplant outside: Apr 24 to May 8Plant for fall: Jun 19 to Jul 10
Start indoors: Mar 20 to Apr 3Transplant outside: May 1 to May 15Plant for fall: Jun 19 to Jul 10
Start indoors: Apr 3 to Apr 17Transplant outside: Jun 5 to Jun 19Sow outdoors: Jun 5 to Jun 19
Start indoors: Apr 3 to Apr 17Transplant outside: May 22 to Jun 5
Sow outdoors: Apr 3 to Apr 24Plant for fall: Jul 3 to Jul 24
Sow outdoors: Apr 3 to Apr 24Plant for fall: Jul 31 to Aug 21
Sow outdoors: Apr 10 to May 22Plant for fall: Aug 14 to Sep 4
Start indoors: Apr 17 to Apr 24Transplant outside: May 29 to Jun 5Sow outdoors: May 22 to Jun 5Plant for fall: Jul 10 to Jul 24
Start indoors: Apr 17 to Apr 24Sow outdoors: May 22 to Jun 5Plant for fall: Jul 17 to Jul 31
Start indoors: Apr 17 to Apr 24Sow outdoors: May 22 to Jun 5
Start indoors: Apr 17 to Apr 24Transplant outside: May 29 to Jun 12
Sow outdoors: Apr 24 to May 22Plant for fall: Jul 3 to Jul 17
Sow outdoors: Apr 24 to May 22Plant for fall: Jul 17 to Jul 31
Sow outdoors: Apr 24 to May 15
Sow outdoors: May 1 to May 29Plant for fall: Jul 17 to Jul 31
Sow outdoors: May 1 to May 22Plant for fall: Jul 31 to Aug 21
Sow outdoors: May 22 to Jun 12Plant for fall: Jul 10 to Jul 24
Sow outdoors: May 22 to Jun 5
Transplant outside: May 29 to Jun 19
Plant for fall: Sep 11 to Oct 16
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Sweet Grass, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 20 – Mar 6 | Apr 17 – May 1 | — | — |
| Peppers | Mar 6 – Mar 20 | May 29 – Jun 12 | — | — |
| Eggplant | Mar 6 – Mar 20 | May 29 – Jun 12 | — | — |
| Tomatoes | Mar 20 – Apr 3 | May 22 – Jun 5 | — | — |
| Lettuce | Mar 20 – Apr 3 | Apr 24 – May 8 | Apr 17 – May 22 | Jul 31 – Aug 28 |
| Kale | Mar 20 – Apr 3 | Apr 17 – May 1 | Apr 17 – May 1 | Jul 17 – Aug 7 |
| Broccoli | Mar 20 – Apr 3 | May 1 – May 15 | — | Jun 19 – Jul 10 |
| Cabbage | Mar 20 – Apr 3 | Apr 24 – May 8 | — | Jun 19 – Jul 10 |
| Cauliflower | Mar 20 – Apr 3 | May 1 – May 15 | — | Jun 19 – Jul 10 |
| Okra | Apr 3 – Apr 17 | Jun 5 – Jun 19 | Jun 5 – Jun 19 | — |
| Basil | Apr 3 – Apr 17 | May 22 – Jun 5 | — | — |
| Peas | — | — | Apr 3 – Apr 24 | Jul 3 – Jul 24 |
| Spinach | — | — | Apr 3 – Apr 24 | Jul 31 – Aug 21 |
| Radishes | — | — | Apr 10 – May 22 | Aug 14 – Sep 4 |
| Cucumbers | Apr 17 – Apr 24 | May 29 – Jun 5 | May 22 – Jun 5 | Jul 10 – Jul 24 |
| Zucchini & Summer Squash | Apr 17 – Apr 24 | — | May 22 – Jun 5 | Jul 17 – Jul 31 |
| Winter Squash & Pumpkins | Apr 17 – Apr 24 | — | May 22 – Jun 5 | — |
| Melons & Watermelon | Apr 17 – Apr 24 | May 29 – Jun 12 | — | — |
| Carrots | — | — | Apr 24 – May 22 | Jul 3 – Jul 17 |
| Beets | — | — | Apr 24 – May 22 | Jul 17 – Jul 31 |
| Potatoes | — | — | Apr 24 – May 15 | — |
| Swiss Chard | — | — | May 1 – May 29 | Jul 17 – Jul 31 |
| Cilantro | — | — | May 1 – May 22 | Jul 31 – Aug 21 |
| Green Beans | — | — | May 22 – Jun 12 | Jul 10 – Jul 24 |
| Sweet Corn | — | — | May 22 – Jun 5 | — |
| Sweet Potatoes | — | May 29 – Jun 19 | — | — |
| Garlic | — | — | — | Sep 11 – Oct 16 |
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 Sweetgrass, MT weather station, about 1 km away (elevation 3,510 ft (1,070 m)).
Frost dates near Sweet Grass
- Sunburst May 17 · Sep 25
- Kevin May 17 · Sep 25
- Oilmont May 17 · Sep 25
- Galata May 23 · Sep 14
- Cut Bank May 24 · Sep 15
- Ethridge May 24 · Sep 15
- Shelby May 23 · Sep 16
- Whitlash frost any month
- Lothair May 24 · Sep 17
- Valier May 17 · Sep 24
Frequently asked questions
When is the last frost in Sweet Grass, MT?
The median last spring frost in Sweet Grass, MT is May 15. There is still about a 10% chance of frost after May 28, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Sweet Grass, MT?
The median first fall frost is September 25, with about a 10% chance of frost before September 11.
How long is the growing season in Sweet Grass, MT?
About 133 days between the median last spring frost and first fall frost.
What planting zone is Sweet Grass, MT?
Sweet Grass, MT is in USDA hardiness zone 4a.