Roy, MT frost dates
Last spring frostMay 14median date
First fall frostSep 24median date
Growing season133 daysfrost-free
Hardiness zone4bZone 4b
How Roy compares
- In 8 years out of 10, the last spring frost in Roy falls between May 3 and May 29, a 26-day window. The first fall frost falls between September 12 and October 7.
- The median last frost is 5 days earlier than the Montana median of May 19.
- Its 133-day growing season is longer than 66% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 6 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 177 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 3 |
| 50% (median) | May 14 |
| 10% (safe for tender plants) | May 29 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 12 |
| 50% (median) | September 24 |
| 90% (late) | October 7 |
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 Roy, MT
Roy, MT frost dates — last frost May 14, first frost Sep 24, zone 4b. whenisthelastfrost.com
Crop
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Start indoors: Feb 19 to Mar 5Transplant outside: Apr 16 to Apr 30
Start indoors: Mar 5 to Mar 19Transplant outside: May 28 to Jun 11
Start indoors: Mar 5 to Mar 19Transplant outside: May 28 to Jun 11
Start indoors: Mar 19 to Apr 2Transplant outside: May 21 to Jun 4
Start indoors: Mar 19 to Apr 2Transplant outside: Apr 23 to May 7Sow outdoors: Apr 16 to May 21Plant for fall: Jul 30 to Aug 27
Start indoors: Mar 19 to Apr 2Transplant outside: Apr 16 to Apr 30Sow outdoors: Apr 16 to Apr 30Plant for fall: Jul 16 to Aug 6
Start indoors: Mar 19 to Apr 2Transplant outside: Apr 30 to May 14Plant for fall: Jun 18 to Jul 9
Start indoors: Mar 19 to Apr 2Transplant outside: Apr 23 to May 7Plant for fall: Jun 18 to Jul 9
Start indoors: Mar 19 to Apr 2Transplant outside: Apr 30 to May 14Plant for fall: Jun 18 to Jul 9
Start indoors: Apr 2 to Apr 16Transplant outside: Jun 4 to Jun 18Sow outdoors: Jun 4 to Jun 18
Start indoors: Apr 2 to Apr 16Transplant outside: May 21 to Jun 4
Sow outdoors: Apr 2 to Apr 23Plant for fall: Jul 2 to Jul 23
Sow outdoors: Apr 2 to Apr 23Plant for fall: Jul 30 to Aug 20
Sow outdoors: Apr 9 to May 21Plant for fall: Aug 13 to Sep 3
Start indoors: Apr 16 to Apr 23Transplant outside: May 28 to Jun 4Sow outdoors: May 21 to Jun 4Plant for fall: Jul 9 to Jul 23
Start indoors: Apr 16 to Apr 23Sow outdoors: May 21 to Jun 4Plant for fall: Jul 16 to Jul 30
Start indoors: Apr 16 to Apr 23Sow outdoors: May 21 to Jun 4
Start indoors: Apr 16 to Apr 23Transplant outside: May 28 to Jun 11
Sow outdoors: Apr 23 to May 21Plant for fall: Jul 2 to Jul 16
Sow outdoors: Apr 23 to May 21Plant for fall: Jul 16 to Jul 30
Sow outdoors: Apr 23 to May 14
Sow outdoors: Apr 30 to May 28Plant for fall: Jul 16 to Jul 30
Sow outdoors: Apr 30 to May 21Plant for fall: Jul 30 to Aug 20
Sow outdoors: May 21 to Jun 11Plant for fall: Jul 9 to Jul 23
Sow outdoors: May 21 to Jun 4
Transplant outside: May 28 to Jun 18
Plant for fall: Sep 10 to Oct 15
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Roy, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 19 – Mar 5 | Apr 16 – Apr 30 | — | — |
| Peppers | Mar 5 – Mar 19 | May 28 – Jun 11 | — | — |
| Eggplant | Mar 5 – Mar 19 | May 28 – Jun 11 | — | — |
| Tomatoes | Mar 19 – Apr 2 | May 21 – Jun 4 | — | — |
| Lettuce | Mar 19 – Apr 2 | Apr 23 – May 7 | Apr 16 – May 21 | Jul 30 – Aug 27 |
| Kale | Mar 19 – Apr 2 | Apr 16 – Apr 30 | Apr 16 – Apr 30 | Jul 16 – Aug 6 |
| Broccoli | Mar 19 – Apr 2 | Apr 30 – May 14 | — | Jun 18 – Jul 9 |
| Cabbage | Mar 19 – Apr 2 | Apr 23 – May 7 | — | Jun 18 – Jul 9 |
| Cauliflower | Mar 19 – Apr 2 | Apr 30 – May 14 | — | Jun 18 – Jul 9 |
| Okra | Apr 2 – Apr 16 | Jun 4 – Jun 18 | Jun 4 – Jun 18 | — |
| Basil | Apr 2 – Apr 16 | May 21 – Jun 4 | — | — |
| Peas | — | — | Apr 2 – Apr 23 | Jul 2 – Jul 23 |
| Spinach | — | — | Apr 2 – Apr 23 | Jul 30 – Aug 20 |
| Radishes | — | — | Apr 9 – May 21 | Aug 13 – Sep 3 |
| Cucumbers | Apr 16 – Apr 23 | May 28 – Jun 4 | May 21 – Jun 4 | Jul 9 – Jul 23 |
| Zucchini & Summer Squash | Apr 16 – Apr 23 | — | May 21 – Jun 4 | Jul 16 – Jul 30 |
| Winter Squash & Pumpkins | Apr 16 – Apr 23 | — | May 21 – Jun 4 | — |
| Melons & Watermelon | Apr 16 – Apr 23 | May 28 – Jun 11 | — | — |
| Carrots | — | — | Apr 23 – May 21 | Jul 2 – Jul 16 |
| Beets | — | — | Apr 23 – May 21 | Jul 16 – Jul 30 |
| Potatoes | — | — | Apr 23 – May 14 | — |
| Swiss Chard | — | — | Apr 30 – May 28 | Jul 16 – Jul 30 |
| Cilantro | — | — | Apr 30 – May 21 | Jul 30 – Aug 20 |
| Green Beans | — | — | May 21 – Jun 11 | Jul 9 – Jul 23 |
| Sweet Corn | — | — | May 21 – Jun 4 | — |
| Sweet Potatoes | — | May 28 – Jun 18 | — | — |
| Garlic | — | — | — | Sep 10 – Oct 15 |
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 Roy 8 Ne, MT weather station, 13 km away (elevation 3,084 ft (940 m)).
Frost dates near Roy
- Grass Range May 20 · Sep 24
- Hilger May 14 · Sep 28
- Winifred May 16 · Sep 23
- Teigen May 20 · Sep 24
- Forest Grove May 19 · Sep 25
- Zortman May 18 · Sep 23
- Lewistown May 14 · Sep 28
- Winnett May 16 · Sep 28
- Hays May 18 · Sep 23
- Lloyd May 23 · Sep 23
Frequently asked questions
When is the last frost in Roy, MT?
The median last spring frost in Roy, MT is May 14. There is still about a 10% chance of frost after May 29, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Roy, MT?
The median first fall frost is September 24, with about a 10% chance of frost before September 12.
How long is the growing season in Roy, MT?
About 133 days between the median last spring frost and first fall frost.
What planting zone is Roy, MT?
Roy, MT is in USDA hardiness zone 4b.