Three Forks, MT frost dates
Last spring frostMay 9median date
First fall frostSep 27median date
Growing season141 daysfrost-free
Hardiness zone5aZone 5a
How Three Forks compares
- In 8 years out of 10, the last spring frost in Three Forks falls between April 29 and May 24, a 25-day window. The first fall frost falls between September 12 and October 9.
- The median last frost is 10 days earlier than the Montana median of May 19.
- Its 141-day growing season is longer than 82% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 6 days later than the zone 5a median of May 3. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5a chart.
- The weather station records an average of 174 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 29 |
| 50% (median) | May 9 |
| 10% (safe for tender plants) | May 24 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 12 |
| 50% (median) | September 27 |
| 90% (late) | October 9 |
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 Three Forks, MT
Three Forks, MT frost dates — last frost May 9, first frost Sep 27, zone 5a. whenisthelastfrost.com
Crop
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Start indoors: Feb 14 to Feb 28Transplant outside: Apr 11 to Apr 25
Start indoors: Feb 28 to Mar 14Transplant outside: May 23 to Jun 6
Start indoors: Feb 28 to Mar 14Transplant outside: May 23 to Jun 6
Start indoors: Mar 14 to Mar 28Transplant outside: May 16 to May 30
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 18 to May 2Sow outdoors: Apr 11 to May 16Plant for fall: Aug 2 to Aug 30
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 11 to Apr 25Sow outdoors: Apr 11 to Apr 25Plant for fall: Jul 19 to Aug 9
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 25 to May 9Plant for fall: Jun 21 to Jul 12
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 18 to May 2Plant for fall: Jun 21 to Jul 12
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 25 to May 9Plant for fall: Jun 21 to Jul 12
Start indoors: Mar 28 to Apr 11Transplant outside: May 30 to Jun 13Sow outdoors: May 30 to Jun 13
Start indoors: Mar 28 to Apr 11Transplant outside: May 16 to May 30
Sow outdoors: Mar 28 to Apr 18Plant for fall: Jul 5 to Jul 26
Sow outdoors: Mar 28 to Apr 18Plant for fall: Aug 2 to Aug 23
Sow outdoors: Apr 4 to May 16Plant for fall: Aug 16 to Sep 6
Start indoors: Apr 11 to Apr 18Transplant outside: May 23 to May 30Sow outdoors: May 16 to May 30Plant for fall: Jul 12 to Jul 26
Start indoors: Apr 11 to Apr 18Sow outdoors: May 16 to May 30Plant for fall: Jul 19 to Aug 2
Start indoors: Apr 11 to Apr 18Sow outdoors: May 16 to May 30
Start indoors: Apr 11 to Apr 18Transplant outside: May 23 to Jun 6
Sow outdoors: Apr 18 to May 16Plant for fall: Jul 5 to Jul 19
Sow outdoors: Apr 18 to May 16Plant for fall: Jul 19 to Aug 2
Sow outdoors: Apr 18 to May 9
Sow outdoors: Apr 25 to May 23Plant for fall: Jul 19 to Aug 2
Sow outdoors: Apr 25 to May 16Plant for fall: Aug 2 to Aug 23
Sow outdoors: May 16 to Jun 6Plant for fall: Jul 12 to Jul 26
Sow outdoors: May 16 to May 30
Transplant outside: May 23 to Jun 13
Plant for fall: Sep 13 to Oct 18
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Three Forks, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 14 – Feb 28 | Apr 11 – Apr 25 | — | — |
| Peppers | Feb 28 – Mar 14 | May 23 – Jun 6 | — | — |
| Eggplant | Feb 28 – Mar 14 | May 23 – Jun 6 | — | — |
| Tomatoes | Mar 14 – Mar 28 | May 16 – May 30 | — | — |
| Lettuce | Mar 14 – Mar 28 | Apr 18 – May 2 | Apr 11 – May 16 | Aug 2 – Aug 30 |
| Kale | Mar 14 – Mar 28 | Apr 11 – Apr 25 | Apr 11 – Apr 25 | Jul 19 – Aug 9 |
| Broccoli | Mar 14 – Mar 28 | Apr 25 – May 9 | — | Jun 21 – Jul 12 |
| Cabbage | Mar 14 – Mar 28 | Apr 18 – May 2 | — | Jun 21 – Jul 12 |
| Cauliflower | Mar 14 – Mar 28 | Apr 25 – May 9 | — | Jun 21 – Jul 12 |
| Okra | Mar 28 – Apr 11 | May 30 – Jun 13 | May 30 – Jun 13 | — |
| Basil | Mar 28 – Apr 11 | May 16 – May 30 | — | — |
| Peas | — | — | Mar 28 – Apr 18 | Jul 5 – Jul 26 |
| Spinach | — | — | Mar 28 – Apr 18 | Aug 2 – Aug 23 |
| Radishes | — | — | Apr 4 – May 16 | Aug 16 – Sep 6 |
| Cucumbers | Apr 11 – Apr 18 | May 23 – May 30 | May 16 – May 30 | Jul 12 – Jul 26 |
| Zucchini & Summer Squash | Apr 11 – Apr 18 | — | May 16 – May 30 | Jul 19 – Aug 2 |
| Winter Squash & Pumpkins | Apr 11 – Apr 18 | — | May 16 – May 30 | — |
| Melons & Watermelon | Apr 11 – Apr 18 | May 23 – Jun 6 | — | — |
| Carrots | — | — | Apr 18 – May 16 | Jul 5 – Jul 19 |
| Beets | — | — | Apr 18 – May 16 | Jul 19 – Aug 2 |
| Potatoes | — | — | Apr 18 – May 9 | — |
| Swiss Chard | — | — | Apr 25 – May 23 | Jul 19 – Aug 2 |
| Cilantro | — | — | Apr 25 – May 16 | Aug 2 – Aug 23 |
| Green Beans | — | — | May 16 – Jun 6 | Jul 12 – Jul 26 |
| Sweet Corn | — | — | May 16 – May 30 | — |
| Sweet Potatoes | — | May 23 – Jun 13 | — | — |
| Garlic | — | — | — | Sep 13 – Oct 18 |
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 Trident, MT weather station, 9 km away (elevation 4,035 ft (1,230 m)).
Frost dates near Three Forks
- Willow Creek May 26 · Sep 15
- Cardwell May 9 · Sep 27
- Manhattan May 26 · Sep 15
- Harrison Apr 30 · Oct 10
- Toston May 19 · Sep 19
- Belgrade May 26 · Sep 16
- Pony Apr 30 · Oct 10
- Radersburg May 19 · Sep 19
- Norris Apr 30 · Oct 10
- Whitehall Jun 13 · Sep 5
Frequently asked questions
When is the last frost in Three Forks, MT?
The median last spring frost in Three Forks, MT is May 9. There is still about a 10% chance of frost after May 24, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Three Forks, MT?
The median first fall frost is September 27, with about a 10% chance of frost before September 12.
How long is the growing season in Three Forks, MT?
About 141 days between the median last spring frost and first fall frost.
What planting zone is Three Forks, MT?
Three Forks, MT is in USDA hardiness zone 5a.