Frost dates for Mosby, 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 5
typical year
Safe to plant
May 26
frost is over in 9 of 10 years
First fall frost
October 4
typical year
Growing season
151 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 7 – 21 | – |
| Spinach | – | Mar 24 – Apr 14 | Aug 9 – 23 |
| Lettuce | – | Apr 7 – 28 | Aug 9 – 23 |
| Radishes | – | Apr 7 – May 19 | Aug 23 – Sep 6 |
| Onions | – | Apr 7 – 21 | – |
| Potatoes | – | Apr 14 – 28 | – |
| Carrots | – | Apr 14 – May 5 | Jul 12 – 26 |
| Beets | – | Apr 7 – 21 | Jul 26 – Aug 9 |
| Kale | Feb 24 – Mar 10 | Apr 7 – 21 | Jul 26 – Aug 9 |
| Broccoli | Feb 24 – Mar 10 | Apr 21 – May 5 | Jul 26 – Aug 9 |
| Cabbage | Feb 10 – 24 | Apr 7 – 21 | Jul 26 – Aug 9 |
| Garlic | – | – | Aug 23 – Sep 13 |
| Warm-season crops | |||
| Tomatoes | Mar 31 – Apr 14 | May 26 – Jun 9 | – |
| Peppers | Mar 24 – Apr 7 | Jun 2 – 16 | – |
| Cucumbers | – | May 26 – Jun 16 | – |
| Zucchini | – | May 26 – Jun 23 | – |
| Pumpkins | – | May 26 – Jun 16 | – |
| Green beans | – | May 26 – Jul 26 | – |
| Sweet corn | – | May 26 – Jun 23 | – |
| Basil | Apr 21 – May 5 | Jun 2 – 9 | – |
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 26 | May 5 | April 20 |
| Fall frost before | September 22 | October 4 | October 19 |
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 April 20 (May 9 in a late year), and the first one in fall around October 14.
Where these dates come from
NOAA weather station MOSBY 4 ENE, MT US (USC00245872), 1991–2020 climate normals. It's the nearest station for 2 zip codes, all within 19 miles:
59058, 59077
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.