Zortman, MT frost dates
Last spring frostMay 18median date
First fall frostSep 23median date
Growing season128 daysfrost-free
Hardiness zone4bZone 4b
How Zortman compares
- In 8 years out of 10, the last spring frost in Zortman falls between May 4 and June 1, a 28-day window. The first fall frost falls between September 7 and October 5.
- The median last frost is 1 day earlier than the Montana median of May 19.
- Its 128-day growing season is longer than 55% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 10 days later than the zone 4b median of May 8. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 4b chart.
- The weather station records an average of 186 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 1 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 7 |
| 50% (median) | September 23 |
| 90% (late) | October 5 |
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 Zortman, MT
Zortman, MT frost dates — last frost May 18, first frost Sep 23, zone 4b. 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 29 to Aug 26
Start indoors: Mar 23 to Apr 6Transplant outside: Apr 20 to May 4Sow outdoors: Apr 20 to May 4Plant for fall: Jul 15 to Aug 5
Start indoors: Mar 23 to Apr 6Transplant outside: May 4 to May 18Plant for fall: Jun 17 to Jul 8
Start indoors: Mar 23 to Apr 6Transplant outside: Apr 27 to May 11Plant for fall: Jun 17 to Jul 8
Start indoors: Mar 23 to Apr 6Transplant outside: May 4 to May 18Plant for fall: Jun 17 to Jul 8
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 1 to Jul 22
Sow outdoors: Apr 6 to Apr 27Plant for fall: Jul 29 to Aug 19
Sow outdoors: Apr 13 to May 25Plant for fall: Aug 12 to Sep 2
Start indoors: Apr 20 to Apr 27Transplant outside: Jun 1 to Jun 8Sow outdoors: May 25 to Jun 8Plant for fall: Jul 8 to Jul 22
Start indoors: Apr 20 to Apr 27Sow outdoors: May 25 to Jun 8Plant for fall: Jul 15 to Jul 29
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 1 to Jul 15
Sow outdoors: Apr 27 to May 25Plant for fall: Jul 15 to Jul 29
Sow outdoors: Apr 27 to May 18
Sow outdoors: May 4 to Jun 1Plant for fall: Jul 15 to Jul 29
Sow outdoors: May 4 to May 25Plant for fall: Jul 29 to Aug 19
Sow outdoors: May 25 to Jun 15Plant for fall: Jul 8 to Jul 22
Sow outdoors: May 25 to Jun 8
Transplant outside: Jun 1 to Jun 22
Plant for fall: Sep 9 to Oct 14
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Zortman, 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 29 – Aug 26 |
| Kale | Mar 23 – Apr 6 | Apr 20 – May 4 | Apr 20 – May 4 | Jul 15 – Aug 5 |
| Broccoli | Mar 23 – Apr 6 | May 4 – May 18 | — | Jun 17 – Jul 8 |
| Cabbage | Mar 23 – Apr 6 | Apr 27 – May 11 | — | Jun 17 – Jul 8 |
| Cauliflower | Mar 23 – Apr 6 | May 4 – May 18 | — | Jun 17 – Jul 8 |
| 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 1 – Jul 22 |
| Spinach | — | — | Apr 6 – Apr 27 | Jul 29 – Aug 19 |
| Radishes | — | — | Apr 13 – May 25 | Aug 12 – Sep 2 |
| Cucumbers | Apr 20 – Apr 27 | Jun 1 – Jun 8 | May 25 – Jun 8 | Jul 8 – Jul 22 |
| Zucchini & Summer Squash | Apr 20 – Apr 27 | — | May 25 – Jun 8 | Jul 15 – Jul 29 |
| 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 1 – Jul 15 |
| Beets | — | — | Apr 27 – May 25 | Jul 15 – Jul 29 |
| Potatoes | — | — | Apr 27 – May 18 | — |
| Swiss Chard | — | — | May 4 – Jun 1 | Jul 15 – Jul 29 |
| Cilantro | — | — | May 4 – May 25 | Jul 29 – Aug 19 |
| Green Beans | — | — | May 25 – Jun 15 | Jul 8 – Jul 22 |
| Sweet Corn | — | — | May 25 – Jun 8 | — |
| Sweet Potatoes | — | Jun 1 – Jun 22 | — | — |
| Garlic | — | — | — | Sep 9 – Oct 14 |
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 Zortman, MT weather station, 17 km away (elevation 4,035 ft (1,230 m)).
Frost dates near Zortman
- Hays May 18 · Sep 23
- Roy May 14 · Sep 24
- Winifred May 16 · Sep 23
- Lloyd May 23 · Sep 23
- Dodson May 10 · Sep 29
- Hilger May 14 · Sep 28
- Teigen May 20 · Sep 24
- Grass Range May 20 · Sep 24
- Harlem May 16 · Sep 21
- Malta May 10 · Sep 29
Frequently asked questions
When is the last frost in Zortman, MT?
The median last spring frost in Zortman, MT is May 18. There is still about a 10% chance of frost after June 1, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Zortman, MT?
The median first fall frost is September 23, with about a 10% chance of frost before September 7.
How long is the growing season in Zortman, MT?
About 128 days between the median last spring frost and first fall frost.
What planting zone is Zortman, MT?
Zortman, MT is in USDA hardiness zone 4b.