Ismay, MT frost dates
Last spring frostMay 22median date
First fall frostSep 15median date
Growing season116 daysfrost-free
Hardiness zone4aZone 4a
How Ismay compares
- In 8 years out of 10, the last spring frost in Ismay falls between May 9 and June 7, a 29-day window. The first fall frost falls between September 2 and October 1.
- The median last frost is 3 days later than the Montana median of May 19.
- Its 116-day growing season is longer than 30% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 10 days later than the zone 4a median of May 12. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 4a chart.
- The weather station records an average of 191 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 9 |
| 50% (median) | May 22 |
| 10% (safe for tender plants) | June 7 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 2 |
| 50% (median) | September 15 |
| 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 Ismay, MT
Ismay, MT frost dates — last frost May 22, first frost Sep 15, zone 4a. whenisthelastfrost.com
Crop
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Start indoors: Feb 27 to Mar 13Transplant outside: Apr 24 to May 8
Start indoors: Mar 13 to Mar 27Transplant outside: Jun 5 to Jun 19
Start indoors: Mar 13 to Mar 27Transplant outside: Jun 5 to Jun 19
Start indoors: Mar 27 to Apr 10Transplant outside: May 29 to Jun 12
Start indoors: Mar 27 to Apr 10Transplant outside: May 1 to May 15Sow outdoors: Apr 24 to May 29Plant for fall: Jul 21 to Aug 18
Start indoors: Mar 27 to Apr 10Transplant outside: Apr 24 to May 8Sow outdoors: Apr 24 to May 8Plant for fall: Jul 7 to Jul 28
Start indoors: Mar 27 to Apr 10Transplant outside: May 8 to May 22Plant for fall: Jun 9 to Jun 30
Start indoors: Mar 27 to Apr 10Transplant outside: May 1 to May 15Plant for fall: Jun 9 to Jun 30
Start indoors: Mar 27 to Apr 10Transplant outside: May 8 to May 22Plant for fall: Jun 9 to Jun 30
Start indoors: Apr 10 to Apr 24Transplant outside: Jun 12 to Jun 26Sow outdoors: Jun 12 to Jun 26
Start indoors: Apr 10 to Apr 24Transplant outside: May 29 to Jun 12
Sow outdoors: Apr 10 to May 1Plant for fall: Jun 23 to Jul 14
Sow outdoors: Apr 10 to May 1Plant for fall: Jul 21 to Aug 11
Sow outdoors: Apr 17 to May 29Plant for fall: Aug 4 to Aug 25
Start indoors: Apr 24 to May 1Transplant outside: Jun 5 to Jun 12Sow outdoors: May 29 to Jun 12Plant for fall: Jun 30 to Jul 14
Start indoors: Apr 24 to May 1Sow outdoors: May 29 to Jun 12Plant for fall: Jul 7 to Jul 21
Start indoors: Apr 24 to May 1Sow outdoors: May 29 to Jun 12
Start indoors: Apr 24 to May 1Transplant outside: Jun 5 to Jun 19
Sow outdoors: May 1 to May 29Plant for fall: Jun 23 to Jul 7
Sow outdoors: May 1 to May 29Plant for fall: Jul 7 to Jul 21
Sow outdoors: May 1 to May 22
Sow outdoors: May 8 to Jun 5Plant for fall: Jul 7 to Jul 21
Sow outdoors: May 8 to May 29Plant for fall: Jul 21 to Aug 11
Sow outdoors: May 29 to Jun 19
Sow outdoors: May 29 to Jun 12
Transplant outside: Jun 5 to Jun 26
Plant for fall: Sep 1 to Oct 6
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Ismay, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 27 – Mar 13 | Apr 24 – May 8 | — | — |
| Peppers | Mar 13 – Mar 27 | Jun 5 – Jun 19 | — | — |
| Eggplant | Mar 13 – Mar 27 | Jun 5 – Jun 19 | — | — |
| Tomatoes | Mar 27 – Apr 10 | May 29 – Jun 12 | — | — |
| Lettuce | Mar 27 – Apr 10 | May 1 – May 15 | Apr 24 – May 29 | Jul 21 – Aug 18 |
| Kale | Mar 27 – Apr 10 | Apr 24 – May 8 | Apr 24 – May 8 | Jul 7 – Jul 28 |
| Broccoli | Mar 27 – Apr 10 | May 8 – May 22 | — | Jun 9 – Jun 30 |
| Cabbage | Mar 27 – Apr 10 | May 1 – May 15 | — | Jun 9 – Jun 30 |
| Cauliflower | Mar 27 – Apr 10 | May 8 – May 22 | — | Jun 9 – Jun 30 |
| Okra | Apr 10 – Apr 24 | Jun 12 – Jun 26 | Jun 12 – Jun 26 | — |
| Basil | Apr 10 – Apr 24 | May 29 – Jun 12 | — | — |
| Peas | — | — | Apr 10 – May 1 | Jun 23 – Jul 14 |
| Spinach | — | — | Apr 10 – May 1 | Jul 21 – Aug 11 |
| Radishes | — | — | Apr 17 – May 29 | Aug 4 – Aug 25 |
| Cucumbers | Apr 24 – May 1 | Jun 5 – Jun 12 | May 29 – Jun 12 | Jun 30 – Jul 14 |
| Zucchini & Summer Squash | Apr 24 – May 1 | — | May 29 – Jun 12 | Jul 7 – Jul 21 |
| Winter Squash & Pumpkins | Apr 24 – May 1 | — | May 29 – Jun 12 | — |
| Melons & Watermelon | Apr 24 – May 1 | Jun 5 – Jun 19 | — | — |
| Carrots | — | — | May 1 – May 29 | Jun 23 – Jul 7 |
| Beets | — | — | May 1 – May 29 | Jul 7 – Jul 21 |
| Potatoes | — | — | May 1 – May 22 | — |
| Swiss Chard | — | — | May 8 – Jun 5 | Jul 7 – Jul 21 |
| Cilantro | — | — | May 8 – May 29 | Jul 21 – Aug 11 |
| Green Beans | — | — | May 29 – Jun 19 | — |
| Sweet Corn | — | — | May 29 – Jun 12 | — |
| Sweet Potatoes | — | Jun 5 – Jun 26 | — | — |
| Garlic | — | — | — | Sep 1 – Oct 6 |
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 Mizpah 4 Nnw, MT weather station, 16 km away (elevation 2,480 ft (756 m)).
Frost dates near Ismay
- Mildred May 20 · Sep 22
- Kinsey May 8 · Sep 30
- Fallon May 20 · Sep 22
- Miles City May 8 · Sep 30
- Terry May 12 · Sep 28
- Plevna May 21 · Sep 20
- Willard May 12 · Sep 26
- Baker May 16 · Sep 26
- Volborg May 18 · Sep 22
- Powderville May 13 · Sep 25
Frequently asked questions
When is the last frost in Ismay, MT?
The median last spring frost in Ismay, MT is May 22. There is still about a 10% chance of frost after June 7, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Ismay, MT?
The median first fall frost is September 15, with about a 10% chance of frost before September 2.
How long is the growing season in Ismay, MT?
About 116 days between the median last spring frost and first fall frost.
What planting zone is Ismay, MT?
Ismay, MT is in USDA hardiness zone 4a.