Westby, MT frost dates
Last spring frostMay 18median date
First fall frostSep 21median date
Growing season126 daysfrost-free
Hardiness zone3bZone 3b
How Westby compares
- In 8 years out of 10, the last spring frost in Westby falls between May 6 and May 30, a 24-day window. The first fall frost falls between September 7 and October 1.
- The median last frost is 1 day earlier than the Montana median of May 19.
- Its 126-day growing season is longer than 53% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is typical for zone 3b, where the median is May 17.
- The weather station records an average of 202 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 6 |
| 50% (median) | May 18 |
| 10% (safe for tender plants) | May 30 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 7 |
| 50% (median) | September 21 |
| 90% (late) | October 1 |
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 Westby, MT
Westby, MT frost dates — last frost May 18, first frost Sep 21, zone 3b. whenisthelastfrost.com
Crop
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Start indoors: Feb 23 to Mar 9Transplant outside: Apr 20 to May 4
Start indoors: Mar 9 to Mar 23Transplant outside: Jun 1 to Jun 15
Start indoors: Mar 9 to Mar 23Transplant outside: Jun 1 to Jun 15
Start indoors: Mar 23 to Apr 6Transplant outside: May 25 to Jun 8
Start indoors: Mar 23 to Apr 6Transplant outside: Apr 27 to May 11Sow outdoors: Apr 20 to May 25Plant for fall: Jul 27 to Aug 24
Start indoors: Mar 23 to Apr 6Transplant outside: Apr 20 to May 4Sow outdoors: Apr 20 to May 4Plant for fall: Jul 13 to Aug 3
Start indoors: Mar 23 to Apr 6Transplant outside: May 4 to May 18Plant for fall: Jun 15 to Jul 6
Start indoors: Mar 23 to Apr 6Transplant outside: Apr 27 to May 11Plant for fall: Jun 15 to Jul 6
Start indoors: Mar 23 to Apr 6Transplant outside: May 4 to May 18Plant for fall: Jun 15 to Jul 6
Start indoors: Apr 6 to Apr 20Transplant outside: Jun 8 to Jun 22Sow outdoors: Jun 8 to Jun 22
Start indoors: Apr 6 to Apr 20Transplant outside: May 25 to Jun 8
Sow outdoors: Apr 6 to Apr 27Plant for fall: Jun 29 to Jul 20
Sow outdoors: Apr 6 to Apr 27Plant for fall: Jul 27 to Aug 17
Sow outdoors: Apr 13 to May 25Plant for fall: Aug 10 to Aug 31
Start indoors: Apr 20 to Apr 27Transplant outside: Jun 1 to Jun 8Sow outdoors: May 25 to Jun 8Plant for fall: Jul 6 to Jul 20
Start indoors: Apr 20 to Apr 27Sow outdoors: May 25 to Jun 8Plant for fall: Jul 13 to Jul 27
Start indoors: Apr 20 to Apr 27Sow outdoors: May 25 to Jun 8
Start indoors: Apr 20 to Apr 27Transplant outside: Jun 1 to Jun 15
Sow outdoors: Apr 27 to May 25Plant for fall: Jun 29 to Jul 13
Sow outdoors: Apr 27 to May 25Plant for fall: Jul 13 to Jul 27
Sow outdoors: Apr 27 to May 18
Sow outdoors: May 4 to Jun 1Plant for fall: Jul 13 to Jul 27
Sow outdoors: May 4 to May 25Plant for fall: Jul 27 to Aug 17
Sow outdoors: May 25 to Jun 15Plant for fall: Jul 6 to Jul 20
Sow outdoors: May 25 to Jun 8
Transplant outside: Jun 1 to Jun 22
Plant for fall: Sep 7 to Oct 12
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Westby, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 23 – Mar 9 | Apr 20 – May 4 | — | — |
| Peppers | Mar 9 – Mar 23 | Jun 1 – Jun 15 | — | — |
| Eggplant | Mar 9 – Mar 23 | Jun 1 – Jun 15 | — | — |
| Tomatoes | Mar 23 – Apr 6 | May 25 – Jun 8 | — | — |
| Lettuce | Mar 23 – Apr 6 | Apr 27 – May 11 | Apr 20 – May 25 | Jul 27 – Aug 24 |
| Kale | Mar 23 – Apr 6 | Apr 20 – May 4 | Apr 20 – May 4 | Jul 13 – Aug 3 |
| Broccoli | Mar 23 – Apr 6 | May 4 – May 18 | — | Jun 15 – Jul 6 |
| Cabbage | Mar 23 – Apr 6 | Apr 27 – May 11 | — | Jun 15 – Jul 6 |
| Cauliflower | Mar 23 – Apr 6 | May 4 – May 18 | — | Jun 15 – Jul 6 |
| Okra | Apr 6 – Apr 20 | Jun 8 – Jun 22 | Jun 8 – Jun 22 | — |
| Basil | Apr 6 – Apr 20 | May 25 – Jun 8 | — | — |
| Peas | — | — | Apr 6 – Apr 27 | Jun 29 – Jul 20 |
| Spinach | — | — | Apr 6 – Apr 27 | Jul 27 – Aug 17 |
| Radishes | — | — | Apr 13 – May 25 | Aug 10 – Aug 31 |
| Cucumbers | Apr 20 – Apr 27 | Jun 1 – Jun 8 | May 25 – Jun 8 | Jul 6 – Jul 20 |
| Zucchini & Summer Squash | Apr 20 – Apr 27 | — | May 25 – Jun 8 | Jul 13 – Jul 27 |
| Winter Squash & Pumpkins | Apr 20 – Apr 27 | — | May 25 – Jun 8 | — |
| Melons & Watermelon | Apr 20 – Apr 27 | Jun 1 – Jun 15 | — | — |
| Carrots | — | — | Apr 27 – May 25 | Jun 29 – Jul 13 |
| Beets | — | — | Apr 27 – May 25 | Jul 13 – Jul 27 |
| Potatoes | — | — | Apr 27 – May 18 | — |
| Swiss Chard | — | — | May 4 – Jun 1 | Jul 13 – Jul 27 |
| Cilantro | — | — | May 4 – May 25 | Jul 27 – Aug 17 |
| Green Beans | — | — | May 25 – Jun 15 | Jul 6 – Jul 20 |
| Sweet Corn | — | — | May 25 – Jun 8 | — |
| Sweet Potatoes | — | Jun 1 – Jun 22 | — | — |
| Garlic | — | — | — | Sep 7 – Oct 12 |
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 Westby, MT weather station, 6 km away (elevation 2,103 ft (641 m)).
Frost dates near Westby
- Dagmar May 16 · Sep 18
- Antelope May 25 · Sep 14
- Plentywood May 25 · Sep 14
- Raymond May 25 · Sep 14
- Outlook May 28 · Sep 7
- Reserve May 16 · Sep 18
- Medicine Lake May 16 · Sep 18
- Homestead May 16 · Sep 18
- Redstone May 28 · Sep 7
- Froid May 16 · Sep 18
Frequently asked questions
When is the last frost in Westby, MT?
The median last spring frost in Westby, MT is May 18. There is still about a 10% chance of frost after May 30, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Westby, MT?
The median first fall frost is September 21, with about a 10% chance of frost before September 7.
How long is the growing season in Westby, MT?
About 126 days between the median last spring frost and first fall frost.
What planting zone is Westby, MT?
Westby, MT is in USDA hardiness zone 3b.