Bynum, MT frost dates
Last spring frostMay 16median date
First fall frostSep 27median date
Growing season134 daysfrost-free
Hardiness zone4bZone 4b
How Bynum compares
- In 8 years out of 10, the last spring frost in Bynum falls between May 2 and May 28, a 26-day window. The first fall frost falls between September 16 and October 9.
- The median last frost is 3 days earlier than the Montana median of May 19.
- Its 134-day growing season is longer than 68% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 8 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 169 nights a year at or below 32°F.
- Compared with Great Falls, MT, 90 km away, the last frost here is 10 days later than there and the growing season is 14 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 2 |
| 50% (median) | May 16 |
| 10% (safe for tender plants) | May 28 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 16 |
| 50% (median) | September 27 |
| 90% (late) | October 9 |
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 Bynum, MT
Bynum, MT frost dates — last frost May 16, first frost Sep 27, zone 4b. 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: Aug 2 to Aug 30
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 18 to May 2Sow outdoors: Apr 18 to May 2Plant for fall: Jul 19 to Aug 9
Start indoors: Mar 21 to Apr 4Transplant outside: May 2 to May 16Plant for fall: Jun 21 to Jul 12
Start indoors: Mar 21 to Apr 4Transplant outside: Apr 25 to May 9Plant for fall: Jun 21 to Jul 12
Start indoors: Mar 21 to Apr 4Transplant outside: May 2 to May 16Plant for fall: Jun 21 to Jul 12
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: Jul 5 to Jul 26
Sow outdoors: Apr 4 to Apr 25Plant for fall: Aug 2 to Aug 23
Sow outdoors: Apr 11 to May 23Plant for fall: Aug 16 to Sep 6
Start indoors: Apr 18 to Apr 25Transplant outside: May 30 to Jun 6Sow outdoors: May 23 to Jun 6Plant for fall: Jul 12 to Jul 26
Start indoors: Apr 18 to Apr 25Sow outdoors: May 23 to Jun 6Plant for fall: Jul 19 to Aug 2
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: Jul 5 to Jul 19
Sow outdoors: Apr 25 to May 23Plant for fall: Jul 19 to Aug 2
Sow outdoors: Apr 25 to May 16
Sow outdoors: May 2 to May 30Plant for fall: Jul 19 to Aug 2
Sow outdoors: May 2 to May 23Plant for fall: Aug 2 to Aug 23
Sow outdoors: May 23 to Jun 13Plant for fall: Jul 12 to Jul 26
Sow outdoors: May 23 to Jun 6
Transplant outside: May 30 to Jun 20
Plant for fall: Sep 13 to Oct 18
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Bynum, 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 | Aug 2 – Aug 30 |
| Kale | Mar 21 – Apr 4 | Apr 18 – May 2 | Apr 18 – May 2 | Jul 19 – Aug 9 |
| Broccoli | Mar 21 – Apr 4 | May 2 – May 16 | — | Jun 21 – Jul 12 |
| Cabbage | Mar 21 – Apr 4 | Apr 25 – May 9 | — | Jun 21 – Jul 12 |
| Cauliflower | Mar 21 – Apr 4 | May 2 – May 16 | — | Jun 21 – Jul 12 |
| 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 | Jul 5 – Jul 26 |
| Spinach | — | — | Apr 4 – Apr 25 | Aug 2 – Aug 23 |
| Radishes | — | — | Apr 11 – May 23 | Aug 16 – Sep 6 |
| Cucumbers | Apr 18 – Apr 25 | May 30 – Jun 6 | May 23 – Jun 6 | Jul 12 – Jul 26 |
| Zucchini & Summer Squash | Apr 18 – Apr 25 | — | May 23 – Jun 6 | Jul 19 – Aug 2 |
| 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 | Jul 5 – Jul 19 |
| Beets | — | — | Apr 25 – May 23 | Jul 19 – Aug 2 |
| Potatoes | — | — | Apr 25 – May 16 | — |
| Swiss Chard | — | — | May 2 – May 30 | Jul 19 – Aug 2 |
| Cilantro | — | — | May 2 – May 23 | Aug 2 – Aug 23 |
| Green Beans | — | — | May 23 – Jun 13 | Jul 12 – Jul 26 |
| Sweet Corn | — | — | May 23 – Jun 6 | — |
| Sweet Potatoes | — | May 30 – Jun 20 | — | — |
| Garlic | — | — | — | Sep 13 – Oct 18 |
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 Bynum 4 Sse, MT weather station, 7 km away (elevation 4,039 ft (1,231 m)).
Frost dates near Bynum
- Pendroy Jun 9 · Sep 3
- Choteau May 28 · Sep 12
- Dupuyer Jun 9 · Sep 3
- Valier May 17 · Sep 24
- Conrad May 20 · Sep 19
- Brady May 20 · Sep 19
- Dutton May 20 · Sep 22
- Fairfield May 13 · Sep 27
- Heart Butte Jun 8 · Sep 5
- Power May 13 · Sep 27
Frequently asked questions
When is the last frost in Bynum, MT?
The median last spring frost in Bynum, MT is May 16. There is still about a 10% chance of frost after May 28, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Bynum, MT?
The median first fall frost is September 27, with about a 10% chance of frost before September 16.
How long is the growing season in Bynum, MT?
About 134 days between the median last spring frost and first fall frost.
What planting zone is Bynum, MT?
Bynum, MT is in USDA hardiness zone 4b.