Frost Dates: First and last frost dates for Lima, 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 24, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around July 11, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before July 2, 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 7 May 1 Apr 27 Apr 24 Apr 20 Apr 17 Apr 14 Apr 10 Apr 4
Last 20° May 21 May 16 May 12 May 9 May 6 May 3 Apr 29 Apr 25 Apr 20
Last 24° Jun 23 Jun 14 Jun 8 Jun 2 May 28 May 23 May 18 May 12 May 3
Last 28° Jul 5 Jun 27 Jun 21 Jun 16 Jun 12 Jun 7 Jun 2 May 28 May 20
Last 32° Jul 16 Jul 9 Jul 5 Jul 1 Jun 27 Jun 23 Jun 19 Jun 15 Jun 8
Last 36° Jul 24 Jul 20 Jul 16 Jul 13 Jul 11 Jul 8 Jul 5 Jul 2 Jun 27

ℹ️ How to read these charts for the fall

As summer ends in Lima, 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 19, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By August 30, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By September 10, 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 10 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 21 Sep 27 Oct 2 Oct 6 Oct 9 Oct 13 Oct 17 Oct 21 Oct 28
First 20° Sep 15 Sep 21 Sep 25 Sep 28 Oct 1 Oct 4 Oct 7 Oct 11 Oct 16
First 24° Sep 6 Sep 11 Sep 15 Sep 18 Sep 21 Sep 24 Sep 27 Oct 1 Oct 6
First 28° Aug 27 Sep 1 Sep 5 Sep 8 Sep 10 Sep 13 Sep 16 Sep 20 Sep 25
First 32° Aug 14 Aug 19 Aug 23 Aug 27 Aug 30 Sep 2 Sep 6 Sep 10 Sep 15
First 36° Aug 4 Aug 10 Aug 13 Aug 17 Aug 20 Aug 23 Aug 26 Aug 30 Sep 4

📍 Frost Dates for other nearby locations

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