Frost Dates: First and last frost dates for Riverside, OR

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 June 1, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around May 13, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before April 30, 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° Mar 8 Feb 22 Feb 13 Feb 5 Jan 28 Jan 20 Jan 11 Dec 30 Dec 9
Last 20° Mar 16 Mar 5 Feb 25 Feb 18 Feb 11 Feb 4 Jan 28 Jan 19 Jan 5
Last 24° Mar 31 Mar 23 Mar 17 Mar 12 Mar 8 Mar 3 Feb 26 Feb 21 Feb 13
Last 28° Apr 16 Apr 11 Apr 7 Apr 4 Apr 1 Mar 29 Mar 25 Mar 22 Mar 16
Last 32° May 6 Apr 30 Apr 26 Apr 22 Apr 19 Apr 16 Apr 12 Apr 8 Apr 2
Last 36° Jun 1 May 25 May 20 May 16 May 13 May 9 May 5 Apr 30 Apr 23

ℹ️ How to read these charts for the fall

As summer ends in Riverside, OR, 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 7, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By September 21, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By October 4, 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 October 4 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° Nov 5 Nov 17 Nov 26 Dec 3 Dec 11 Dec 18 Dec 27 Jan 8 --
First 20° Oct 26 Nov 5 Nov 13 Nov 19 Nov 25 Dec 1 Dec 8 Dec 16 Dec 29
First 24° Oct 1 Oct 9 Oct 15 Oct 20 Oct 24 Oct 29 Nov 3 Nov 8 Nov 16
First 28° Sep 9 Sep 17 Sep 23 Sep 28 Oct 2 Oct 7 Oct 12 Oct 17 Oct 25
First 32° Aug 31 Sep 7 Sep 12 Sep 17 Sep 21 Sep 25 Sep 29 Oct 4 Oct 11
First 36° Aug 26 Sep 1 Sep 6 Sep 10 Sep 14 Sep 18 Sep 22 Sep 27 Oct 3

📍 Frost Dates for other nearby locations

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