Heron, MT frost dates
Last spring frostMay 20median date
First fall frostSep 20median date
Growing season123 daysfrost-free
Hardiness zone6bZone 6b
How Heron compares
- In 8 years out of 10, the last spring frost in Heron falls between May 4 and June 5, a 32-day window. The first fall frost falls between September 1 and October 5.
- The median last frost is 1 day later than the Montana median of May 19.
- Its 123-day growing season is longer than 41% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 28 days later than the zone 6b median of Apr 22. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 6b chart.
- The weather station records an average of 174 nights a year at or below 32°F.
- Compared with Spokane, WA, 117 km away, the last frost here is 24 days later than there and the growing season is 49 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 4 |
| 50% (median) | May 20 |
| 10% (safe for tender plants) | June 5 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 1 |
| 50% (median) | September 20 |
| 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 Heron, MT
Heron, MT frost dates — last frost May 20, first frost Sep 20, zone 6b. whenisthelastfrost.com
Crop
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Start indoors: Feb 25 to Mar 11Transplant outside: Apr 22 to May 6
Start indoors: Mar 11 to Mar 25Transplant outside: Jun 3 to Jun 17
Start indoors: Mar 11 to Mar 25Transplant outside: Jun 3 to Jun 17
Start indoors: Mar 25 to Apr 8Transplant outside: May 27 to Jun 10
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 29 to May 13Sow outdoors: Apr 22 to May 27Plant for fall: Jul 26 to Aug 23
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 22 to May 6Sow outdoors: Apr 22 to May 6Plant for fall: Jul 12 to Aug 2
Start indoors: Mar 25 to Apr 8Transplant outside: May 6 to May 20Plant for fall: Jun 14 to Jul 5
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 29 to May 13Plant for fall: Jun 14 to Jul 5
Start indoors: Mar 25 to Apr 8Transplant outside: May 6 to May 20Plant for fall: Jun 14 to Jul 5
Start indoors: Apr 8 to Apr 22Transplant outside: Jun 10 to Jun 24Sow outdoors: Jun 10 to Jun 24
Start indoors: Apr 8 to Apr 22Transplant outside: May 27 to Jun 10
Sow outdoors: Apr 8 to Apr 29Plant for fall: Jun 28 to Jul 19
Sow outdoors: Apr 8 to Apr 29Plant for fall: Jul 26 to Aug 16
Sow outdoors: Apr 15 to May 27Plant for fall: Aug 9 to Aug 30
Start indoors: Apr 22 to Apr 29Transplant outside: Jun 3 to Jun 10Sow outdoors: May 27 to Jun 10Plant for fall: Jul 5 to Jul 19
Start indoors: Apr 22 to Apr 29Sow outdoors: May 27 to Jun 10Plant for fall: Jul 12 to Jul 26
Start indoors: Apr 22 to Apr 29Sow outdoors: May 27 to Jun 10
Start indoors: Apr 22 to Apr 29Transplant outside: Jun 3 to Jun 17
Sow outdoors: Apr 29 to May 27Plant for fall: Jun 28 to Jul 12
Sow outdoors: Apr 29 to May 27Plant for fall: Jul 12 to Jul 26
Sow outdoors: Apr 29 to May 20
Sow outdoors: May 6 to Jun 3Plant for fall: Jul 12 to Jul 26
Sow outdoors: May 6 to May 27Plant for fall: Jul 26 to Aug 16
Sow outdoors: May 27 to Jun 17Plant for fall: Jul 5 to Jul 19
Sow outdoors: May 27 to Jun 10
Transplant outside: Jun 3 to Jun 24
Plant for fall: Sep 6 to Oct 11
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Heron, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 25 – Mar 11 | Apr 22 – May 6 | — | — |
| Peppers | Mar 11 – Mar 25 | Jun 3 – Jun 17 | — | — |
| Eggplant | Mar 11 – Mar 25 | Jun 3 – Jun 17 | — | — |
| Tomatoes | Mar 25 – Apr 8 | May 27 – Jun 10 | — | — |
| Lettuce | Mar 25 – Apr 8 | Apr 29 – May 13 | Apr 22 – May 27 | Jul 26 – Aug 23 |
| Kale | Mar 25 – Apr 8 | Apr 22 – May 6 | Apr 22 – May 6 | Jul 12 – Aug 2 |
| Broccoli | Mar 25 – Apr 8 | May 6 – May 20 | — | Jun 14 – Jul 5 |
| Cabbage | Mar 25 – Apr 8 | Apr 29 – May 13 | — | Jun 14 – Jul 5 |
| Cauliflower | Mar 25 – Apr 8 | May 6 – May 20 | — | Jun 14 – Jul 5 |
| Okra | Apr 8 – Apr 22 | Jun 10 – Jun 24 | Jun 10 – Jun 24 | — |
| Basil | Apr 8 – Apr 22 | May 27 – Jun 10 | — | — |
| Peas | — | — | Apr 8 – Apr 29 | Jun 28 – Jul 19 |
| Spinach | — | — | Apr 8 – Apr 29 | Jul 26 – Aug 16 |
| Radishes | — | — | Apr 15 – May 27 | Aug 9 – Aug 30 |
| Cucumbers | Apr 22 – Apr 29 | Jun 3 – Jun 10 | May 27 – Jun 10 | Jul 5 – Jul 19 |
| Zucchini & Summer Squash | Apr 22 – Apr 29 | — | May 27 – Jun 10 | Jul 12 – Jul 26 |
| Winter Squash & Pumpkins | Apr 22 – Apr 29 | — | May 27 – Jun 10 | — |
| Melons & Watermelon | Apr 22 – Apr 29 | Jun 3 – Jun 17 | — | — |
| Carrots | — | — | Apr 29 – May 27 | Jun 28 – Jul 12 |
| Beets | — | — | Apr 29 – May 27 | Jul 12 – Jul 26 |
| Potatoes | — | — | Apr 29 – May 20 | — |
| Swiss Chard | — | — | May 6 – Jun 3 | Jul 12 – Jul 26 |
| Cilantro | — | — | May 6 – May 27 | Jul 26 – Aug 16 |
| Green Beans | — | — | May 27 – Jun 17 | Jul 5 – Jul 19 |
| Sweet Corn | — | — | May 27 – Jun 10 | — |
| Sweet Potatoes | — | Jun 3 – Jun 24 | — | — |
| Garlic | — | — | — | Sep 6 – Oct 11 |
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 Heron 2 Nw, MT weather station, 5 km away (elevation 2,241 ft (683 m)).
Frost dates near Heron
- Noxon May 20 · Sep 20
- Trout Creek May 20 · Sep 21
- Libby May 10 · Sep 26
- Troy May 14 · Sep 25
- Thompson Falls May 7 · Oct 4
- Saltese frost any month
- Haugan frost any month
- De Borgia frost any month
- Marion frost any month
- Saint Regis frost any month
Frequently asked questions
When is the last frost in Heron, MT?
The median last spring frost in Heron, MT is May 20. There is still about a 10% chance of frost after June 5, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Heron, MT?
The median first fall frost is September 20, with about a 10% chance of frost before September 1.
How long is the growing season in Heron, MT?
About 123 days between the median last spring frost and first fall frost.
What planting zone is Heron, MT?
Heron, MT is in USDA hardiness zone 6b.