Harlem, MT frost dates
Last spring frostMay 16median date
First fall frostSep 21median date
Growing season128 daysfrost-free
Hardiness zone4aZone 4a
How Harlem compares
- In 8 years out of 10, the last spring frost in Harlem falls between May 4 and May 31, a 27-day window. The first fall frost falls between September 8 and October 2.
- The median last frost is 3 days 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 4 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 192 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 4 |
| 50% (median) | May 16 |
| 10% (safe for tender plants) | May 31 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 8 |
| 50% (median) | September 21 |
| 90% (late) | October 2 |
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 Harlem, MT
Harlem, MT frost dates — last frost May 16, first frost Sep 21, zone 4a. whenisthelastfrost.com
Crop
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Start indoors: Feb 21 to Mar 7Transplant outside: Apr 18 to May 2
Start indoors: Mar 7 to Mar 21Transplant outside: May 30 to Jun 13
Start indoors: Mar 7 to Mar 21Transplant outside: May 30 to Jun 13
Start indoors: Mar 21 to Apr 4Transplant outside: May 23 to Jun 6
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 25 to May 9Sow outdoors: Apr 18 to May 23Plant for fall: Jul 27 to Aug 24
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 18 to May 2Sow outdoors: Apr 18 to May 2Plant for fall: Jul 13 to Aug 3
Start indoors: Mar 21 to Apr 4Transplant outside: May 2 to May 16Plant for fall: Jun 15 to Jul 6
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 25 to May 9Plant for fall: Jun 15 to Jul 6
Start indoors: Mar 21 to Apr 4Transplant outside: May 2 to May 16Plant for fall: Jun 15 to Jul 6
Start indoors: Apr 4 to Apr 18Transplant outside: Jun 6 to Jun 20Sow outdoors: Jun 6 to Jun 20
Start indoors: Apr 4 to Apr 18Transplant outside: May 23 to Jun 6
Sow outdoors: Apr 4 to Apr 25Plant for fall: Jun 29 to Jul 20
Sow outdoors: Apr 4 to Apr 25Plant for fall: Jul 27 to Aug 17
Sow outdoors: Apr 11 to May 23Plant for fall: Aug 10 to Aug 31
Start indoors: Apr 18 to Apr 25Transplant outside: May 30 to Jun 6Sow outdoors: May 23 to Jun 6Plant for fall: Jul 6 to Jul 20
Start indoors: Apr 18 to Apr 25Sow outdoors: May 23 to Jun 6Plant for fall: Jul 13 to Jul 27
Start indoors: Apr 18 to Apr 25Sow outdoors: May 23 to Jun 6
Start indoors: Apr 18 to Apr 25Transplant outside: May 30 to Jun 13
Sow outdoors: Apr 25 to May 23Plant for fall: Jun 29 to Jul 13
Sow outdoors: Apr 25 to May 23Plant for fall: Jul 13 to Jul 27
Sow outdoors: Apr 25 to May 16
Sow outdoors: May 2 to May 30Plant for fall: Jul 13 to Jul 27
Sow outdoors: May 2 to May 23Plant for fall: Jul 27 to Aug 17
Sow outdoors: May 23 to Jun 13Plant for fall: Jul 6 to Jul 20
Sow outdoors: May 23 to Jun 6
Transplant outside: May 30 to Jun 20
Plant for fall: Sep 7 to Oct 12
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Harlem, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 21 – Mar 7 | Apr 18 – May 2 | — | — |
| Peppers | Mar 7 – Mar 21 | May 30 – Jun 13 | — | — |
| Eggplant | Mar 7 – Mar 21 | May 30 – Jun 13 | — | — |
| Tomatoes | Mar 21 – Apr 4 | May 23 – Jun 6 | — | — |
| Lettuce | Mar 21 – Apr 4 | Apr 25 – May 9 | Apr 18 – May 23 | Jul 27 – Aug 24 |
| Kale | Mar 21 – Apr 4 | Apr 18 – May 2 | Apr 18 – May 2 | Jul 13 – Aug 3 |
| Broccoli | Mar 21 – Apr 4 | May 2 – May 16 | — | Jun 15 – Jul 6 |
| Cabbage | Mar 21 – Apr 4 | Apr 25 – May 9 | — | Jun 15 – Jul 6 |
| Cauliflower | Mar 21 – Apr 4 | May 2 – May 16 | — | Jun 15 – Jul 6 |
| Okra | Apr 4 – Apr 18 | Jun 6 – Jun 20 | Jun 6 – Jun 20 | — |
| Basil | Apr 4 – Apr 18 | May 23 – Jun 6 | — | — |
| Peas | — | — | Apr 4 – Apr 25 | Jun 29 – Jul 20 |
| Spinach | — | — | Apr 4 – Apr 25 | Jul 27 – Aug 17 |
| Radishes | — | — | Apr 11 – May 23 | Aug 10 – Aug 31 |
| Cucumbers | Apr 18 – Apr 25 | May 30 – Jun 6 | May 23 – Jun 6 | Jul 6 – Jul 20 |
| Zucchini & Summer Squash | Apr 18 – Apr 25 | — | May 23 – Jun 6 | Jul 13 – Jul 27 |
| Winter Squash & Pumpkins | Apr 18 – Apr 25 | — | May 23 – Jun 6 | — |
| Melons & Watermelon | Apr 18 – Apr 25 | May 30 – Jun 13 | — | — |
| Carrots | — | — | Apr 25 – May 23 | Jun 29 – Jul 13 |
| Beets | — | — | Apr 25 – May 23 | Jul 13 – Jul 27 |
| Potatoes | — | — | Apr 25 – May 16 | — |
| Swiss Chard | — | — | May 2 – May 30 | Jul 13 – Jul 27 |
| Cilantro | — | — | May 2 – May 23 | Jul 27 – Aug 17 |
| Green Beans | — | — | May 23 – Jun 13 | Jul 6 – Jul 20 |
| Sweet Corn | — | — | May 23 – Jun 6 | — |
| Sweet Potatoes | — | May 30 – Jun 20 | — | — |
| 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 Harlem, MT weather station, 2 km away (elevation 2,372 ft (723 m)).
Frost dates near Harlem
- Zurich May 14 · Sep 23
- Chinook May 14 · Sep 23
- Hogeland May 19 · Sep 21
- Dodson May 10 · Sep 29
- Turner May 19 · Sep 21
- Hays May 18 · Sep 23
- Havre May 15 · Sep 23
- Malta May 10 · Sep 29
- Loring May 19 · Sep 22
- Lloyd May 23 · Sep 23
Frequently asked questions
When is the last frost in Harlem, MT?
The median last spring frost in Harlem, MT is May 16. There is still about a 10% chance of frost after May 31, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Harlem, MT?
The median first fall frost is September 21, with about a 10% chance of frost before September 8.
How long is the growing season in Harlem, MT?
About 128 days between the median last spring frost and first fall frost.
What planting zone is Harlem, MT?
Harlem, MT is in USDA hardiness zone 4a.