Thompson Falls, MT frost dates
Last spring frostMay 7median date
First fall frostOct 4median date
Growing season150 daysfrost-free
Hardiness zone6aZone 6a
How Thompson Falls compares
- In 8 years out of 10, the last spring frost in Thompson Falls falls between April 25 and May 19, a 24-day window. The first fall frost falls between September 21 and October 19.
- The median last frost is 12 days earlier than the Montana median of May 19.
- Its 150-day growing season is longer than 95% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 8 days later than the zone 6a median of Apr 29. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 6a chart.
- The weather station records an average of 148 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 25 |
| 50% (median) | May 7 |
| 10% (safe for tender plants) | May 19 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 21 |
| 50% (median) | October 4 |
| 90% (late) | October 19 |
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 Thompson Falls, MT
Thompson Falls, MT frost dates — last frost May 7, first frost Oct 4, zone 6a. whenisthelastfrost.com
Crop
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Start indoors: Feb 12 to Feb 26Transplant outside: Apr 9 to Apr 23
Start indoors: Feb 26 to Mar 12Transplant outside: May 21 to Jun 4
Start indoors: Feb 26 to Mar 12Transplant outside: May 21 to Jun 4
Start indoors: Mar 12 to Mar 26Transplant outside: May 14 to May 28
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 16 to Apr 30Sow outdoors: Apr 9 to May 14Plant for fall: Aug 9 to Sep 6
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 9 to Apr 23Sow outdoors: Apr 9 to Apr 23Plant for fall: Jul 26 to Aug 16
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 23 to May 7Plant for fall: Jun 28 to Jul 19
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 16 to Apr 30Plant for fall: Jun 28 to Jul 19
Start indoors: Mar 12 to Mar 26Transplant outside: Apr 23 to May 7Plant for fall: Jun 28 to Jul 19
Start indoors: Mar 26 to Apr 9Transplant outside: May 28 to Jun 11Sow outdoors: May 28 to Jun 11
Start indoors: Mar 26 to Apr 9Transplant outside: May 14 to May 28
Sow outdoors: Mar 26 to Apr 16Plant for fall: Jul 12 to Aug 2
Sow outdoors: Mar 26 to Apr 16Plant for fall: Aug 9 to Aug 30
Sow outdoors: Apr 2 to May 14Plant for fall: Aug 23 to Sep 13
Start indoors: Apr 9 to Apr 16Transplant outside: May 21 to May 28Sow outdoors: May 14 to May 28Plant for fall: Jul 19 to Aug 2
Start indoors: Apr 9 to Apr 16Sow outdoors: May 14 to May 28Plant for fall: Jul 26 to Aug 9
Start indoors: Apr 9 to Apr 16Sow outdoors: May 14 to May 28
Start indoors: Apr 9 to Apr 16Transplant outside: May 21 to Jun 4
Sow outdoors: Apr 16 to May 14Plant for fall: Jul 12 to Jul 26
Sow outdoors: Apr 16 to May 14Plant for fall: Jul 26 to Aug 9
Sow outdoors: Apr 16 to May 7
Sow outdoors: Apr 23 to May 21Plant for fall: Jul 26 to Aug 9
Sow outdoors: Apr 23 to May 14Plant for fall: Aug 9 to Aug 30
Sow outdoors: May 14 to Jun 4Plant for fall: Jul 19 to Aug 2
Sow outdoors: May 14 to May 28
Transplant outside: May 21 to Jun 11
Plant for fall: Sep 20 to Oct 25
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Thompson Falls, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 12 – Feb 26 | Apr 9 – Apr 23 | — | — |
| Peppers | Feb 26 – Mar 12 | May 21 – Jun 4 | — | — |
| Eggplant | Feb 26 – Mar 12 | May 21 – Jun 4 | — | — |
| Tomatoes | Mar 12 – Mar 26 | May 14 – May 28 | — | — |
| Lettuce | Mar 12 – Mar 26 | Apr 16 – Apr 30 | Apr 9 – May 14 | Aug 9 – Sep 6 |
| Kale | Mar 12 – Mar 26 | Apr 9 – Apr 23 | Apr 9 – Apr 23 | Jul 26 – Aug 16 |
| Broccoli | Mar 12 – Mar 26 | Apr 23 – May 7 | — | Jun 28 – Jul 19 |
| Cabbage | Mar 12 – Mar 26 | Apr 16 – Apr 30 | — | Jun 28 – Jul 19 |
| Cauliflower | Mar 12 – Mar 26 | Apr 23 – May 7 | — | Jun 28 – Jul 19 |
| Okra | Mar 26 – Apr 9 | May 28 – Jun 11 | May 28 – Jun 11 | — |
| Basil | Mar 26 – Apr 9 | May 14 – May 28 | — | — |
| Peas | — | — | Mar 26 – Apr 16 | Jul 12 – Aug 2 |
| Spinach | — | — | Mar 26 – Apr 16 | Aug 9 – Aug 30 |
| Radishes | — | — | Apr 2 – May 14 | Aug 23 – Sep 13 |
| Cucumbers | Apr 9 – Apr 16 | May 21 – May 28 | May 14 – May 28 | Jul 19 – Aug 2 |
| Zucchini & Summer Squash | Apr 9 – Apr 16 | — | May 14 – May 28 | Jul 26 – Aug 9 |
| Winter Squash & Pumpkins | Apr 9 – Apr 16 | — | May 14 – May 28 | — |
| Melons & Watermelon | Apr 9 – Apr 16 | May 21 – Jun 4 | — | — |
| Carrots | — | — | Apr 16 – May 14 | Jul 12 – Jul 26 |
| Beets | — | — | Apr 16 – May 14 | Jul 26 – Aug 9 |
| Potatoes | — | — | Apr 16 – May 7 | — |
| Swiss Chard | — | — | Apr 23 – May 21 | Jul 26 – Aug 9 |
| Cilantro | — | — | Apr 23 – May 14 | Aug 9 – Aug 30 |
| Green Beans | — | — | May 14 – Jun 4 | Jul 19 – Aug 2 |
| Sweet Corn | — | — | May 14 – May 28 | — |
| Sweet Potatoes | — | May 21 – Jun 11 | — | — |
| Garlic | — | — | — | Sep 20 – Oct 25 |
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 Thompson Falls Ph, MT weather station, about 1 km away (elevation 2,379 ft (725 m)).
Frost dates near Thompson Falls
- De Borgia frost any month
- Saltese frost any month
- Haugan frost any month
- Trout Creek May 20 · Sep 21
- Saint Regis frost any month
- Plains frost any month
- Paradise May 17 · Sep 23
- Hot Springs May 15 · Sep 28
- Lonepine May 15 · Sep 28
- Superior May 17 · Sep 23
Frequently asked questions
When is the last frost in Thompson Falls, MT?
The median last spring frost in Thompson Falls, MT is May 7. There is still about a 10% chance of frost after May 19, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Thompson Falls, MT?
The median first fall frost is October 4, with about a 10% chance of frost before September 21.
How long is the growing season in Thompson Falls, MT?
About 150 days between the median last spring frost and first fall frost.
What planting zone is Thompson Falls, MT?
Thompson Falls, MT is in USDA hardiness zone 6a.