Frost dates for Roy, MT
When the last spring frost and first fall frost usually come, and when to plant, from 30 years of NOAA weather records.
Last spring frost
May 14
typical year
Safe to plant
May 29
frost is over in 9 of 10 years
First fall frost
September 24
typical year
Growing season
134 days
frost-free, typical year
Frost watch this week
Tonight's and the next six nights' lows from the National Weather Service forecast for the station's location. Frost: 32°F or colder. Possible frost: 33–36°F, mostly in low spots on clear, still nights.
When to plant
Counted from this page's frost dates. Warm-season crops wait for the safe-to-plant date.
| Crop | Start indoors | Plant outside | Fall planting |
|---|---|---|---|
| Cool-season crops | |||
| Peas | – | Apr 16 – 30 | – |
| Spinach | – | Apr 2 – 23 | Jul 30 – Aug 13 |
| Lettuce | – | Apr 16 – May 7 | Jul 30 – Aug 13 |
| Radishes | – | Apr 16 – May 28 | Aug 13 – 27 |
| Onions | – | Apr 16 – 30 | – |
| Potatoes | – | Apr 23 – May 7 | – |
| Carrots | – | Apr 23 – May 14 | Jul 2 – 16 |
| Beets | – | Apr 16 – 30 | Jul 16 – 30 |
| Kale | Mar 5 – 19 | Apr 16 – 30 | Jul 16 – 30 |
| Broccoli | Mar 5 – 19 | Apr 30 – May 14 | Jul 16 – 30 |
| Cabbage | Feb 19 – Mar 5 | Apr 16 – 30 | Jul 16 – 30 |
| Garlic | – | – | Aug 13 – Sep 3 |
| Warm-season crops | |||
| Tomatoes | Apr 3 – 17 | May 29 – Jun 12 | – |
| Peppers | Mar 27 – Apr 10 | Jun 5 – 19 | – |
| Cucumbers | – | May 29 – Jun 19 | – |
| Zucchini | – | May 29 – Jun 26 | – |
| Pumpkins | – | May 29 – Jun 19 | – |
| Green beans | – | May 29 – Jul 16 | – |
| Sweet corn | – | May 29 – Jun 26 | – |
| Basil | Apr 24 – May 8 | Jun 5 – 12 | – |
Onions: from sets. Green beans: until 10 weeks before the first fall frost. Garlic: harvest next summer.
The year at a glance
Start indoors Plant outside Fall planting
The chance of frost, by date
| 1 year in 10 | Half of years | 9 years in 10 | |
|---|---|---|---|
| Spring frost after | May 29 | May 14 | May 3 |
| Fall frost before | September 12 | September 24 | October 7 |
Frost here means 32°F or colder. Read across: in 1 year in 10, spring frost carries on past the first date, which is why that date is the safe-to-plant date.
Hard freeze (28°F)
A hard freeze kills most garden plants, even hardy ones. The last one in spring usually comes around May 2 (May 15 in a late year), and the first one in fall around October 2.
Where these dates come from
NOAA weather station ROY 8 NE, MT US (USC00247228), 1991–2020 climate normals. It's the nearest station for 1 zip code, all within 5 miles:
59471
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.