Dillon, MT frost dates
Last spring frostJun 5median date
First fall frostSep 13median date
Growing season100 daysfrost-free
Hardiness zone5aZone 5a
How Dillon compares
- In 8 years out of 10, the last spring frost in Dillon falls between May 18 and June 23, a 36-day window. The first fall frost falls between August 29 and September 27.
- The median last frost is 17 days later than the Montana median of May 19.
- Its 100-day growing season is longer than 11% of the 325 Montana places with a regular frost season (state median 125 days).
- The last frost is 33 days later than the zone 5a median of May 3. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5a chart.
- The weather station records an average of 189 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 18 |
| 50% (median) | June 5 |
| 10% (safe for tender plants) | June 23 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | August 29 |
| 50% (median) | September 13 |
| 90% (late) | September 27 |
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 Dillon, MT
Dillon, MT frost dates — last frost Jun 5, first frost Sep 13, zone 5a. whenisthelastfrost.com
Crop
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Start indoors: Mar 13 to Mar 27Transplant outside: May 8 to May 22
Start indoors: Mar 27 to Apr 10Transplant outside: Jun 19 to Jul 3
Start indoors: Mar 27 to Apr 10Transplant outside: Jun 19 to Jul 3
Start indoors: Apr 10 to Apr 24Transplant outside: Jun 12 to Jun 26
Start indoors: Apr 10 to Apr 24Transplant outside: May 15 to May 29Sow outdoors: May 8 to Jun 12Plant for fall: Jul 19 to Aug 16
Start indoors: Apr 10 to Apr 24Transplant outside: May 8 to May 22Sow outdoors: May 8 to May 22Plant for fall: Jul 5 to Jul 26
Start indoors: Apr 10 to Apr 24Transplant outside: May 22 to Jun 5
Start indoors: Apr 10 to Apr 24Transplant outside: May 15 to May 29
Start indoors: Apr 10 to Apr 24Transplant outside: May 22 to Jun 5
Start indoors: Apr 24 to May 8Transplant outside: Jun 26 to Jul 10Sow outdoors: Jun 26 to Jul 10
Start indoors: Apr 24 to May 8Transplant outside: Jun 12 to Jun 26
Sow outdoors: Apr 24 to May 15Plant for fall: Jun 21 to Jul 12
Sow outdoors: Apr 24 to May 15Plant for fall: Jul 19 to Aug 9
Sow outdoors: May 1 to Jun 12Plant for fall: Aug 2 to Aug 23
Start indoors: May 8 to May 15Transplant outside: Jun 19 to Jun 26Sow outdoors: Jun 12 to Jun 26
Start indoors: May 8 to May 15Sow outdoors: Jun 12 to Jun 26
Start indoors: May 8 to May 15Sow outdoors: Jun 12 to Jun 26
Start indoors: May 8 to May 15Transplant outside: Jun 19 to Jul 3
Sow outdoors: May 15 to Jun 12
Sow outdoors: May 15 to Jun 12Plant for fall: Jul 5 to Jul 19
Sow outdoors: May 15 to Jun 5
Sow outdoors: May 22 to Jun 19Plant for fall: Jul 5 to Jul 19
Sow outdoors: May 22 to Jun 12Plant for fall: Jul 19 to Aug 9
Sow outdoors: Jun 12 to Jul 3
Sow outdoors: Jun 12 to Jun 26
Transplant outside: Jun 19 to Jul 10
Plant for fall: Aug 30 to Oct 4
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Dillon, MT
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Mar 13 – Mar 27 | May 8 – May 22 | — | — |
| Peppers | Mar 27 – Apr 10 | Jun 19 – Jul 3 | — | — |
| Eggplant | Mar 27 – Apr 10 | Jun 19 – Jul 3 | — | — |
| Tomatoes | Apr 10 – Apr 24 | Jun 12 – Jun 26 | — | — |
| Lettuce | Apr 10 – Apr 24 | May 15 – May 29 | May 8 – Jun 12 | Jul 19 – Aug 16 |
| Kale | Apr 10 – Apr 24 | May 8 – May 22 | May 8 – May 22 | Jul 5 – Jul 26 |
| Broccoli | Apr 10 – Apr 24 | May 22 – Jun 5 | — | — |
| Cabbage | Apr 10 – Apr 24 | May 15 – May 29 | — | — |
| Cauliflower | Apr 10 – Apr 24 | May 22 – Jun 5 | — | — |
| Okra | Apr 24 – May 8 | Jun 26 – Jul 10 | Jun 26 – Jul 10 | — |
| Basil | Apr 24 – May 8 | Jun 12 – Jun 26 | — | — |
| Peas | — | — | Apr 24 – May 15 | Jun 21 – Jul 12 |
| Spinach | — | — | Apr 24 – May 15 | Jul 19 – Aug 9 |
| Radishes | — | — | May 1 – Jun 12 | Aug 2 – Aug 23 |
| Cucumbers | May 8 – May 15 | Jun 19 – Jun 26 | Jun 12 – Jun 26 | — |
| Zucchini & Summer Squash | May 8 – May 15 | — | Jun 12 – Jun 26 | — |
| Winter Squash & Pumpkins Warning: Your frost-free season is about 100 days, which is tight for winter squash & pumpkins (100+ days). Choose early varieties and use transplants or row covers. | May 8 – May 15 | — | Jun 12 – Jun 26 | — |
| Melons & Watermelon | May 8 – May 15 | Jun 19 – Jul 3 | — | — |
| Carrots | — | — | May 15 – Jun 12 | — |
| Beets | — | — | May 15 – Jun 12 | Jul 5 – Jul 19 |
| Potatoes | — | — | May 15 – Jun 5 | — |
| Swiss Chard | — | — | May 22 – Jun 19 | Jul 5 – Jul 19 |
| Cilantro | — | — | May 22 – Jun 12 | Jul 19 – Aug 9 |
| Green Beans | — | — | Jun 12 – Jul 3 | — |
| Sweet Corn | — | — | Jun 12 – Jun 26 | — |
| Sweet Potatoes Warning: Your frost-free season is about 100 days, which is tight for sweet potatoes (100+ days). Choose early varieties and use transplants or row covers. | — | Jun 19 – Jul 10 | — | — |
| Garlic | — | — | — | Aug 30 – Oct 4 |
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 Dillon U Of Montana Western, MT weather station, 3 km away (elevation 5,128 ft (1,563 m)).
Frost dates near Dillon
- Glen frost any month
- Twin Bridges Jun 8 · Sep 2
- Polaris frost any month
- Sheridan May 24 · Sep 22
- Melrose frost any month
- Alder frost any month
- Virginia City Jun 4 · Sep 18
- Dell Jun 11 · Sep 10
- Jackson frost any month
- Silver Star Jun 8 · Sep 2
Frequently asked questions
When is the last frost in Dillon, MT?
The median last spring frost in Dillon, MT is June 5. There is still about a 10% chance of frost after June 23, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Dillon, MT?
The median first fall frost is September 13, with about a 10% chance of frost before August 29.
How long is the growing season in Dillon, MT?
About 100 days between the median last spring frost and first fall frost.
What planting zone is Dillon, MT?
Dillon, MT is in USDA hardiness zone 5a.