Decker, MT frost dates
Last spring frostMay 18median date
First fall frostSep 24median date
Growing season129 daysfrost-free
Hardiness zone5aZone 5a
How Decker compares
- In 8 years out of 10, the last spring frost in Decker falls between May 4 and June 2, a 29-day window. The first fall frost falls between September 9 and October 7.
- The median last frost is 1 day earlier than the Montana median of May 19.
- Its 129-day growing season is longer than 57% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 15 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 200 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 4 |
| 50% (median) | May 18 |
| 10% (safe for tender plants) | June 2 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 9 |
| 50% (median) | September 24 |
| 90% (late) | October 7 |
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 Decker, MT
Decker, MT frost dates — last frost May 18, first frost Sep 24, zone 5a. 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 30 to Aug 27
Start indoors: Mar 23 to Apr 6Transplant outside: Apr 20 to May 4Sow outdoors: Apr 20 to May 4Plant for fall: Jul 16 to Aug 6
Start indoors: Mar 23 to Apr 6Transplant outside: May 4 to May 18Plant for fall: Jun 18 to Jul 9
Start indoors: Mar 23 to Apr 6Transplant outside: Apr 27 to May 11Plant for fall: Jun 18 to Jul 9
Start indoors: Mar 23 to Apr 6Transplant outside: May 4 to May 18Plant for fall: Jun 18 to Jul 9
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: Jul 2 to Jul 23
Sow outdoors: Apr 6 to Apr 27Plant for fall: Jul 30 to Aug 20
Sow outdoors: Apr 13 to May 25Plant for fall: Aug 13 to Sep 3
Start indoors: Apr 20 to Apr 27Transplant outside: Jun 1 to Jun 8Sow outdoors: May 25 to Jun 8Plant for fall: Jul 9 to Jul 23
Start indoors: Apr 20 to Apr 27Sow outdoors: May 25 to Jun 8Plant for fall: Jul 16 to Jul 30
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: Jul 2 to Jul 16
Sow outdoors: Apr 27 to May 25Plant for fall: Jul 16 to Jul 30
Sow outdoors: Apr 27 to May 18
Sow outdoors: May 4 to Jun 1Plant for fall: Jul 16 to Jul 30
Sow outdoors: May 4 to May 25Plant for fall: Jul 30 to Aug 20
Sow outdoors: May 25 to Jun 15Plant for fall: Jul 9 to Jul 23
Sow outdoors: May 25 to Jun 8
Transplant outside: Jun 1 to Jun 22
Plant for fall: Sep 10 to Oct 15
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Decker, 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 30 – Aug 27 |
| Kale | Mar 23 – Apr 6 | Apr 20 – May 4 | Apr 20 – May 4 | Jul 16 – Aug 6 |
| Broccoli | Mar 23 – Apr 6 | May 4 – May 18 | — | Jun 18 – Jul 9 |
| Cabbage | Mar 23 – Apr 6 | Apr 27 – May 11 | — | Jun 18 – Jul 9 |
| Cauliflower | Mar 23 – Apr 6 | May 4 – May 18 | — | Jun 18 – Jul 9 |
| 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 | Jul 2 – Jul 23 |
| Spinach | — | — | Apr 6 – Apr 27 | Jul 30 – Aug 20 |
| Radishes | — | — | Apr 13 – May 25 | Aug 13 – Sep 3 |
| Cucumbers | Apr 20 – Apr 27 | Jun 1 – Jun 8 | May 25 – Jun 8 | Jul 9 – Jul 23 |
| Zucchini & Summer Squash | Apr 20 – Apr 27 | — | May 25 – Jun 8 | Jul 16 – Jul 30 |
| 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 | Jul 2 – Jul 16 |
| Beets | — | — | Apr 27 – May 25 | Jul 16 – Jul 30 |
| Potatoes | — | — | Apr 27 – May 18 | — |
| Swiss Chard | — | — | May 4 – Jun 1 | Jul 16 – Jul 30 |
| Cilantro | — | — | May 4 – May 25 | Jul 30 – Aug 20 |
| Green Beans | — | — | May 25 – Jun 15 | Jul 9 – Jul 23 |
| Sweet Corn | — | — | May 25 – Jun 8 | — |
| Sweet Potatoes | — | Jun 1 – Jun 22 | — | — |
| 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 Sheridan Fld Stn, WY weather station, 38 km away (elevation 3,750 ft (1,143 m)).
Frost dates near Decker
- Birney May 23 · Sep 15
- Busby May 23 · Sep 15
- Lodge Grass May 21 · Sep 17
- Wyola May 21 · Sep 17
- Lame Deer May 23 · Sep 15
- Otter May 14 · Sep 30
- Garryowen May 13 · Sep 29
- Ashland May 18 · Sep 22
- Crow Agency May 13 · Sep 29
- Saint Xavier May 7 · Oct 5
Frequently asked questions
When is the last frost in Decker, MT?
The median last spring frost in Decker, MT is May 18. There is still about a 10% chance of frost after June 2, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Decker, MT?
The median first fall frost is September 24, with about a 10% chance of frost before September 9.
How long is the growing season in Decker, MT?
About 129 days between the median last spring frost and first fall frost.
What planting zone is Decker, MT?
Decker, MT is in USDA hardiness zone 5a.