Frost Dates: First and last frost dates for Libby, 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 July 12, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around June 21, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before June 6, 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° Apr 2 Mar 22 Mar 14 Mar 8 Mar 2 Feb 24 Feb 17 Feb 10 Jan 30
Last 20° Apr 25 Apr 16 Apr 10 Apr 5 Apr 1 Mar 27 Mar 22 Mar 16 Mar 7
Last 24° May 5 Apr 29 Apr 25 Apr 22 Apr 19 Apr 15 Apr 12 Apr 8 Apr 2
Last 28° May 28 May 23 May 18 May 15 May 12 May 8 May 5 May 1 Apr 25
Last 32° Jun 26 Jun 18 Jun 13 Jun 8 Jun 3 May 30 May 25 May 19 May 11
Last 36° Jul 12 Jul 5 Jun 29 Jun 25 Jun 21 Jun 16 Jun 12 Jun 6 May 30

ℹ️ How to read these charts for the fall

As summer ends in Libby, 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 September 3, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By September 14, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By September 24, 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 September 24 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° Oct 24 Nov 4 Nov 11 Nov 18 Nov 24 Nov 30 Dec 7 Dec 14 Dec 25
First 20° Oct 4 Oct 15 Oct 22 Oct 29 Nov 4 Nov 11 Nov 17 Nov 25 Dec 6
First 24° Sep 22 Oct 2 Oct 8 Oct 14 Oct 19 Oct 25 Oct 30 Nov 6 Nov 15
First 28° Sep 12 Sep 18 Sep 23 Sep 27 Oct 1 Oct 5 Oct 9 Oct 14 Oct 21
First 32° Aug 29 Sep 3 Sep 7 Sep 11 Sep 14 Sep 17 Sep 20 Sep 24 Sep 29
First 36° Aug 16 Aug 22 Aug 26 Aug 30 Sep 2 Sep 5 Sep 9 Sep 13 Sep 19

📍 Frost Dates for other nearby locations

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