Frost dates for 59626 — Helena, MT
Last spring frostMay 9median date
First fall frostSep 30median date
Growing season144 daysfrost-free
Hardiness zone4bZone 4b
How Helena compares
- In 8 years out of 10, the last spring frost in Helena falls between April 29 and May 25, a 26-day window. The first fall frost falls between September 17 and October 11.
- The median last frost is 10 days earlier than the Montana median of May 19.
- Its 144-day growing season is longer than 88% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is typical for zone 4b, where the median is May 8.
- The weather station records an average of 170 nights a year at or below 32°F.
- Compared with Great Falls, MT, 119 km away, the last frost here is 3 days later than there and the growing season is 4 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 29 |
| 50% (median) | May 9 |
| 10% (safe for tender plants) | May 25 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 17 |
| 50% (median) | September 30 |
| 90% (late) | October 11 |
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 Helena, MT
Frost dates for 59626 — Helena, MT — last frost May 9, first frost Sep 30, zone 4b. whenisthelastfrost.com
Crop
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Start indoors: Feb 14 to Feb 28Transplant outside: Apr 11 to Apr 25
Start indoors: Feb 28 to Mar 14Transplant outside: May 23 to Jun 6
Start indoors: Feb 28 to Mar 14Transplant outside: May 23 to Jun 6
Start indoors: Mar 14 to Mar 28Transplant outside: May 16 to May 30
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 18 to May 2Sow outdoors: Apr 11 to May 16Plant for fall: Aug 5 to Sep 2
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 11 to Apr 25Sow outdoors: Apr 11 to Apr 25Plant for fall: Jul 22 to Aug 12
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 25 to May 9Plant for fall: Jun 24 to Jul 15
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 18 to May 2Plant for fall: Jun 24 to Jul 15
Start indoors: Mar 14 to Mar 28Transplant outside: Apr 25 to May 9Plant for fall: Jun 24 to Jul 15
Start indoors: Mar 28 to Apr 11Transplant outside: May 30 to Jun 13Sow outdoors: May 30 to Jun 13
Start indoors: Mar 28 to Apr 11Transplant outside: May 16 to May 30
Sow outdoors: Mar 28 to Apr 18Plant for fall: Jul 8 to Jul 29
Sow outdoors: Mar 28 to Apr 18Plant for fall: Aug 5 to Aug 26
Sow outdoors: Apr 4 to May 16Plant for fall: Aug 19 to Sep 9
Start indoors: Apr 11 to Apr 18Transplant outside: May 23 to May 30Sow outdoors: May 16 to May 30Plant for fall: Jul 15 to Jul 29
Start indoors: Apr 11 to Apr 18Sow outdoors: May 16 to May 30Plant for fall: Jul 22 to Aug 5
Start indoors: Apr 11 to Apr 18Sow outdoors: May 16 to May 30
Start indoors: Apr 11 to Apr 18Transplant outside: May 23 to Jun 6
Sow outdoors: Apr 18 to May 16Plant for fall: Jul 8 to Jul 22
Sow outdoors: Apr 18 to May 16Plant for fall: Jul 22 to Aug 5
Sow outdoors: Apr 18 to May 9
Sow outdoors: Apr 25 to May 23Plant for fall: Jul 22 to Aug 5
Sow outdoors: Apr 25 to May 16Plant for fall: Aug 5 to Aug 26
Sow outdoors: May 16 to Jun 6Plant for fall: Jul 15 to Jul 29
Sow outdoors: May 16 to May 30
Transplant outside: May 23 to Jun 13
Plant for fall: Sep 16 to Oct 21
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Helena, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 14 – Feb 28 | Apr 11 – Apr 25 | — | — |
| Peppers | Feb 28 – Mar 14 | May 23 – Jun 6 | — | — |
| Eggplant | Feb 28 – Mar 14 | May 23 – Jun 6 | — | — |
| Tomatoes | Mar 14 – Mar 28 | May 16 – May 30 | — | — |
| Lettuce | Mar 14 – Mar 28 | Apr 18 – May 2 | Apr 11 – May 16 | Aug 5 – Sep 2 |
| Kale | Mar 14 – Mar 28 | Apr 11 – Apr 25 | Apr 11 – Apr 25 | Jul 22 – Aug 12 |
| Broccoli | Mar 14 – Mar 28 | Apr 25 – May 9 | — | Jun 24 – Jul 15 |
| Cabbage | Mar 14 – Mar 28 | Apr 18 – May 2 | — | Jun 24 – Jul 15 |
| Cauliflower | Mar 14 – Mar 28 | Apr 25 – May 9 | — | Jun 24 – Jul 15 |
| Okra | Mar 28 – Apr 11 | May 30 – Jun 13 | May 30 – Jun 13 | — |
| Basil | Mar 28 – Apr 11 | May 16 – May 30 | — | — |
| Peas | — | — | Mar 28 – Apr 18 | Jul 8 – Jul 29 |
| Spinach | — | — | Mar 28 – Apr 18 | Aug 5 – Aug 26 |
| Radishes | — | — | Apr 4 – May 16 | Aug 19 – Sep 9 |
| Cucumbers | Apr 11 – Apr 18 | May 23 – May 30 | May 16 – May 30 | Jul 15 – Jul 29 |
| Zucchini & Summer Squash | Apr 11 – Apr 18 | — | May 16 – May 30 | Jul 22 – Aug 5 |
| Winter Squash & Pumpkins | Apr 11 – Apr 18 | — | May 16 – May 30 | — |
| Melons & Watermelon | Apr 11 – Apr 18 | May 23 – Jun 6 | — | — |
| Carrots | — | — | Apr 18 – May 16 | Jul 8 – Jul 22 |
| Beets | — | — | Apr 18 – May 16 | Jul 22 – Aug 5 |
| Potatoes | — | — | Apr 18 – May 9 | — |
| Swiss Chard | — | — | Apr 25 – May 23 | Jul 22 – Aug 5 |
| Cilantro | — | — | Apr 25 – May 16 | Aug 5 – Aug 26 |
| Green Beans | — | — | May 16 – Jun 6 | Jul 15 – Jul 29 |
| Sweet Corn | — | — | May 16 – May 30 | — |
| Sweet Potatoes | — | May 23 – Jun 13 | — | — |
| Garlic | — | — | — | Sep 16 – Oct 21 |
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 Helena Rgnl Ap, MT weather station, 6 km away (elevation 3,829 ft (1,167 m)).
ZIP codes in Helena: 59601 59602 59604 59620 59623 59624 59625 59626
Frost dates near Helena
- Fort Harrison May 9 · Sep 30
- East Helena May 9 · Sep 30
- Clancy Jun 18 · Sep 5
- Jefferson City Jun 18 · Sep 5
- Canyon Creek Jun 4 · Sep 14
- Marysville Jun 4 · Sep 14
- Elliston Jun 9 · Sep 8
- Basin Jun 7 · Sep 8
Frequently asked questions
When is the last frost in Helena, MT?
The median last spring frost in Helena, MT is May 9. There is still about a 10% chance of frost after May 25, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Helena, MT?
The median first fall frost is September 30, with about a 10% chance of frost before September 17.
How long is the growing season in Helena, MT?
About 144 days between the median last spring frost and first fall frost.
What planting zone is Helena, MT?
Helena, MT is in USDA hardiness zone 4b.