Roundup, MT frost dates
Last spring frostMay 20median date
First fall frostSep 21median date
Growing season124 daysfrost-free
Hardiness zone4bZone 4b
How Roundup compares
- In 8 years out of 10, the last spring frost in Roundup falls between May 6 and June 2, a 27-day window. The first fall frost falls between September 5 and October 4.
- The median last frost is 1 day later than the Montana median of May 19.
- Its 124-day growing season is longer than 45% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 12 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 163 nights a year at or below 32°F.
- Compared with Billings, MT, 71 km away, the last frost here is 16 days later than there and the growing season is 32 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 6 |
| 50% (median) | May 20 |
| 10% (safe for tender plants) | June 2 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 5 |
| 50% (median) | September 21 |
| 90% (late) | October 4 |
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 Roundup, MT
Roundup, MT frost dates — last frost May 20, first frost Sep 21, zone 4b. 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 27 to Aug 24
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 22 to May 6Sow outdoors: Apr 22 to May 6Plant for fall: Jul 13 to Aug 3
Start indoors: Mar 25 to Apr 8Transplant outside: May 6 to May 20Plant for fall: Jun 15 to Jul 6
Start indoors: Mar 25 to Apr 8Transplant outside: Apr 29 to May 13Plant for fall: Jun 15 to Jul 6
Start indoors: Mar 25 to Apr 8Transplant outside: May 6 to May 20Plant for fall: Jun 15 to Jul 6
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 29 to Jul 20
Sow outdoors: Apr 8 to Apr 29Plant for fall: Jul 27 to Aug 17
Sow outdoors: Apr 15 to May 27Plant for fall: Aug 10 to Aug 31
Start indoors: Apr 22 to Apr 29Transplant outside: Jun 3 to Jun 10Sow outdoors: May 27 to Jun 10Plant for fall: Jul 6 to Jul 20
Start indoors: Apr 22 to Apr 29Sow outdoors: May 27 to Jun 10Plant for fall: Jul 13 to Jul 27
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 29 to Jul 13
Sow outdoors: Apr 29 to May 27Plant for fall: Jul 13 to Jul 27
Sow outdoors: Apr 29 to May 20
Sow outdoors: May 6 to Jun 3Plant for fall: Jul 13 to Jul 27
Sow outdoors: May 6 to May 27Plant for fall: Jul 27 to Aug 17
Sow outdoors: May 27 to Jun 17Plant for fall: Jul 6 to Jul 20
Sow outdoors: May 27 to Jun 10
Transplant outside: Jun 3 to Jun 24
Plant for fall: Sep 7 to Oct 12
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Roundup, 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 27 – Aug 24 |
| Kale | Mar 25 – Apr 8 | Apr 22 – May 6 | Apr 22 – May 6 | Jul 13 – Aug 3 |
| Broccoli | Mar 25 – Apr 8 | May 6 – May 20 | — | Jun 15 – Jul 6 |
| Cabbage | Mar 25 – Apr 8 | Apr 29 – May 13 | — | Jun 15 – Jul 6 |
| Cauliflower | Mar 25 – Apr 8 | May 6 – May 20 | — | Jun 15 – Jul 6 |
| 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 29 – Jul 20 |
| Spinach | — | — | Apr 8 – Apr 29 | Jul 27 – Aug 17 |
| Radishes | — | — | Apr 15 – May 27 | Aug 10 – Aug 31 |
| Cucumbers | Apr 22 – Apr 29 | Jun 3 – Jun 10 | May 27 – Jun 10 | Jul 6 – Jul 20 |
| Zucchini & Summer Squash | Apr 22 – Apr 29 | — | May 27 – Jun 10 | Jul 13 – Jul 27 |
| 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 29 – Jul 13 |
| Beets | — | — | Apr 29 – May 27 | Jul 13 – Jul 27 |
| Potatoes | — | — | Apr 29 – May 20 | — |
| Swiss Chard | — | — | May 6 – Jun 3 | Jul 13 – Jul 27 |
| Cilantro | — | — | May 6 – May 27 | Jul 27 – Aug 17 |
| Green Beans | — | — | May 27 – Jun 17 | Jul 6 – Jul 20 |
| Sweet Corn | — | — | May 27 – Jun 10 | — |
| Sweet Potatoes | — | Jun 3 – Jun 24 | — | — |
| 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 Roundup, MT weather station, about 1 km away (elevation 3,199 ft (975 m)).
ZIP codes in Roundup: 59072 59073
Frost dates near Roundup
- Musselshell May 10 · Sep 29
- Lavina May 22 · Sep 15
- Broadview May 22 · Sep 15
- Melstone May 10 · Sep 29
- Shepherd May 12 · Sep 25
- Acton May 4 · Oct 7
- Worden May 12 · Sep 25
- Ryegate May 17 · Sep 23
- Winnett May 16 · Sep 28
- Ballantine May 12 · Sep 25
Frequently asked questions
When is the last frost in Roundup, MT?
The median last spring frost in Roundup, MT is May 20. There is still about a 10% chance of frost after June 2, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Roundup, MT?
The median first fall frost is September 21, with about a 10% chance of frost before September 5.
How long is the growing season in Roundup, MT?
About 124 days between the median last spring frost and first fall frost.
What planting zone is Roundup, MT?
Roundup, MT is in USDA hardiness zone 4b.