Frost dates for Tiber Dam, 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 16
typical year
Safe to plant
May 30
frost is over in 9 of 10 years
First fall frost
September 23
typical year
Growing season
129 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 18 – May 2 | – |
| Spinach | – | Apr 4 – 25 | Jul 29 – Aug 12 |
| Lettuce | – | Apr 18 – May 9 | Jul 29 – Aug 12 |
| Radishes | – | Apr 18 – May 30 | Aug 12 – 26 |
| Onions | – | Apr 18 – May 2 | – |
| Potatoes | – | Apr 25 – May 9 | – |
| Carrots | – | Apr 25 – May 16 | Jul 1 – 15 |
| Beets | – | Apr 18 – May 2 | Jul 15 – 29 |
| Kale | Mar 7 – 21 | Apr 18 – May 2 | Jul 15 – 29 |
| Broccoli | Mar 7 – 21 | May 2 – 16 | Jul 15 – 29 |
| Cabbage | Feb 21 – Mar 7 | Apr 18 – May 2 | Jul 15 – 29 |
| Garlic | – | – | Aug 12 – Sep 2 |
| Warm-season crops | |||
| Tomatoes | Apr 4 – 18 | May 30 – Jun 13 | – |
| Peppers | Mar 28 – Apr 11 | Jun 6 – 20 | – |
| Cucumbers | – | May 30 – Jun 20 | – |
| Zucchini | – | May 30 – Jun 27 | – |
| Pumpkins | – | May 30 – Jun 20 | – |
| Green beans | – | May 30 – Jul 15 | – |
| Sweet corn | – | May 30 – Jun 27 | – |
| Basil | Apr 25 – May 9 | Jun 6 – 13 | – |
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 30 | May 16 | May 2 |
| Fall frost before | September 9 | September 23 | October 3 |
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 3 (May 17 in a late year), and the first one in fall around October 1.
Where these dates come from
NOAA weather station TIBER DAM, MT US (USC00248233), 1991–2020 climate normals. It's the nearest station for 1 zip code, all within 13 miles:
59456
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.