Frost Dates: First and last frost dates for Charles City, IA

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 May 26, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around May 11, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before May 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° Apr 8 Apr 2 Mar 29 Mar 26 Mar 23 Mar 20 Mar 17 Mar 13 Mar 7
Last 20° Apr 13 Apr 8 Apr 4 Apr 1 Mar 29 Mar 26 Mar 22 Mar 18 Mar 13
Last 24° Apr 20 Apr 16 Apr 12 Apr 9 Apr 7 Apr 4 Apr 1 Mar 29 Mar 24
Last 28° Apr 27 Apr 22 Apr 19 Apr 16 Apr 14 Apr 11 Apr 8 Apr 5 Mar 31
Last 32° May 11 May 7 May 4 May 1 Apr 29 Apr 26 Apr 24 Apr 21 Apr 16
Last 36° May 26 May 21 May 17 May 14 May 11 May 8 May 5 May 2 Apr 27

ℹ️ How to read these charts for the fall

As summer ends in Charles City, IA, 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 24, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By October 2, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By October 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 October 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° Oct 26 Nov 1 Nov 6 Nov 9 Nov 13 Nov 16 Nov 20 Nov 24 Nov 30
First 20° Oct 19 Oct 24 Oct 28 Oct 31 Nov 3 Nov 6 Nov 9 Nov 13 Nov 18
First 24° Oct 7 Oct 13 Oct 18 Oct 21 Oct 25 Oct 28 Nov 1 Nov 5 Nov 11
First 28° Sep 24 Sep 29 Oct 3 Oct 7 Oct 10 Oct 13 Oct 17 Oct 21 Oct 27
First 32° Sep 20 Sep 24 Sep 27 Sep 30 Oct 2 Oct 4 Oct 7 Oct 10 Oct 14
First 36° Sep 11 Sep 15 Sep 18 Sep 20 Sep 23 Sep 25 Sep 27 Sep 30 Oct 4

📍 Frost Dates for other nearby locations

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