Frost Dates: First and last frost dates for Alturas, CA

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 31, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around July 17, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before July 7, 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 25 Apr 17 Apr 10 Apr 5 Mar 31 Mar 26 Mar 20 Mar 14 Mar 5
Last 20° May 15 May 9 May 4 Apr 30 Apr 27 Apr 23 Apr 19 Apr 15 Apr 8
Last 24° Jun 3 May 27 May 22 May 17 May 13 May 9 May 5 Apr 30 Apr 22
Last 28° Jun 26 Jun 18 Jun 12 Jun 7 Jun 2 May 29 May 24 May 18 May 10
Last 32° Jul 18 Jul 12 Jul 8 Jul 4 Jun 30 Jun 26 Jun 22 Jun 18 Jun 12
Last 36° Jul 31 Jul 26 Jul 23 Jul 20 Jul 17 Jul 14 Jul 11 Jul 7 Jul 2

ℹ️ How to read these charts for the fall

As summer ends in Alturas, CA, 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 9, 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 9 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 7 Oct 13 Oct 18 Oct 21 Oct 25 Oct 28 Nov 1 Nov 5 Nov 11
First 20° Sep 27 Oct 3 Oct 8 Oct 12 Oct 16 Oct 19 Oct 23 Oct 28 Nov 3
First 24° Sep 16 Sep 21 Sep 25 Sep 28 Oct 1 Oct 4 Oct 7 Oct 11 Oct 17
First 28° Aug 30 Sep 4 Sep 8 Sep 11 Sep 14 Sep 17 Sep 20 Sep 24 Sep 29
First 32° Aug 14 Aug 19 Aug 23 Aug 26 Aug 30 Sep 2 Sep 5 Sep 9 Sep 14
First 36° Aug 1 Aug 5 Aug 8 Aug 11 Aug 13 Aug 16 Aug 18 Aug 21 Aug 26

📍 Frost Dates for other nearby locations

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