Frost Dates: First and last frost dates for Sula, MT

ℹ️ How to read these charts for the spring

As spring unfolds, the risk of frost gradually decreases each day until your tender plants are finally safe. The probabilities shown in the chart help you make smart decisions about when to plant.

While frost typically forms at 32°F, tender plants can be damaged even when temperatures are slightly higher. Air temperatures are often measured several feet above the ground, but temperatures at plant level can be several degrees colder. Protected areas like porches help by blocking radiational cooling. Given these variables, we consider 36°F the "caution zone" for frost-sensitive plants.

Key dates for your spring planting:

  • By August 3, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around July 25, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before July 18, there's still an 80% risk of frost — too early for tomatoes and other tender plants unless you're prepared to protect them

If the 10-day forecast shows no temperatures below 40°F, you might safely plant earlier than the above dates suggest. Many gardeners watch for this weather window to get a head start on the growing season.

In the Spring
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Last 16° May 10 May 2 Apr 26 Apr 20 Apr 16 Apr 11 Apr 5 Mar 30 Mar 22
Last 20° May 21 May 15 May 11 May 7 May 4 Apr 30 Apr 26 Apr 22 Apr 16
Last 24° Jun 15 Jun 8 Jun 2 May 28 May 24 May 19 May 14 May 9 May 1
Last 28° Jul 10 Jul 3 Jun 27 Jun 22 Jun 18 Jun 13 Jun 8 Jun 3 May 26
Last 32° Jul 31 Jul 25 Jul 20 Jul 16 Jul 13 Jul 9 Jul 6 Jul 1 Jun 25
Last 36° Aug 3 Jul 31 Jul 29 Jul 27 Jul 25 Jul 23 Jul 21 Jul 18 Jul 15

ℹ️ How to read these charts for the fall

As summer ends in Sula, MT, nighttime temperatures begin to drop, and your risk of frost increases with each passing day. Knowing when to expect frost helps you harvest sensitive crops and extend your growing season with protection methods.

The chart below shows the probability of experiencing specific temperatures on various dates. Here's what this means for your garden:

1
Early warning: Around August 5, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By August 15, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By August 25, there's an 80% chance of seeing 32°F — most tender plants will be damaged without protection
4
Another perspective: You have only a 1 in 5 chance of making it past August 25 without a freezing night

These probabilities help you time your end-of-season harvests and know when to apply protective measures like row covers, cloches, or cold frames to extend your harvest.

In the Fall
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
First 16° Sep 15 Sep 22 Sep 27 Oct 1 Oct 5 Oct 9 Oct 13 Oct 18 Oct 25
First 20° Sep 9 Sep 14 Sep 17 Sep 21 Sep 24 Sep 26 Sep 30 Oct 3 Oct 8
First 24° Sep 2 Sep 7 Sep 10 Sep 12 Sep 15 Sep 17 Sep 20 Sep 23 Sep 27
First 28° Aug 17 Aug 23 Aug 27 Aug 30 Sep 2 Sep 5 Sep 8 Sep 12 Sep 18
First 32° Jul 31 Aug 5 Aug 9 Aug 12 Aug 15 Aug 18 Aug 22 Aug 25 Aug 31
First 36° Jul 29 Jul 31 Aug 3 Aug 5 Aug 6 Aug 8 Aug 10 Aug 12 Aug 15

📍 Frost Dates for other nearby locations

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Data is provided by the NOAA National Centers for Environmental Information.