Frost Dates: First and last frost dates for Fort Collins, Colorado

How to read these charts for the fall
As your growing season comes to an end, the nightly temperatures for Fort Collins, Colorado start to go down, and therefore every day that goes by increases the chance that you'll get frost. Your risk of frost really begins around September 18, and by October 12 you're almost certain to have received at least one frost event.

The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:

  1. You have a small 20% chance of getting 32° by September 23.
  2. There is a 50% chance of being hit by a 32° frost starting around October 2
  3. You have a 80% chance of seeing 32° by October 12
  4. Said another way, you have a 1 in 5 chance at making it to that day without a 32° night.
In the Fall
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
First 16° Oct 29 Nov 3 Nov 6 Nov 9 Nov 11 Nov 14 Nov 17 Nov 20 Nov 24
First 20° Oct 19 Oct 24 Oct 28 Oct 31 Nov 3 Nov 6 Nov 10 Nov 14 Nov 19
First 24° Oct 4 Oct 10 Oct 14 Oct 18 Oct 21 Oct 25 Oct 28 Nov 1 Nov 7
First 28° Sep 24 Sep 30 Oct 4 Oct 7 Oct 10 Oct 13 Oct 17 Oct 21 Oct 26
First 32° Sep 18 Sep 23 Sep 26 Sep 29 Oct 2 Oct 5 Oct 8 Oct 12 Oct 17
First 36° Sep 15 Sep 18 Sep 20 Sep 22 Sep 24 Sep 26 Sep 28 Oct 1 Oct 4

How to read these charts for the spring
As the growing season approaches, the days get longer, the weather begins to warm up, and the nights start being less cold. You're still getting frost, but the chance of nightly frosts gets less and less with each passing day. Eventually, the frost stops, and this is when your tender plants are fully safe. So, how do you plan for this? The probabilities on this page help you assess your risk of frost on any given day.

What's a safe temperature for tender plants? When the nightly temperature falls, frost can form, even above 32°, because the air is colder high above the ground and the frost can form up there and then fall down onto your garden and do some damage, even if it's 36° on the ground. So many factors come into play, including wind, concrete, houses, trees and other structures, etc etc etc. Because of all this, you might want to consider 36° as "the danger zone".

In your average springtime, you have a 90% chance that there will be no 36° nights by May 27. In other words, you can pretty much count on being safe from frost by that day. But we want to get those tomatoes in the ground as soon as possible, right? We see that there's still an 80% chance of 36° on May 4, so we don't dare plant that early. We wait a few days and by May 13 we are at the 50/50 point. At this point, we are close and we can start watching the weather forecast. If the upcoming week's forecast doesn't show below 40°, then it's probably okay to risk planting out your plants. If conditions change and a surprise frost does threaten, there's always things you can do to protect plants from frost.

In the Spring
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Last 16° Apr 11 Apr 4 Mar 30 Mar 25 Mar 21 Mar 17 Mar 13 Mar 8 Mar 1
Last 20° Apr 16 Apr 10 Apr 6 Apr 2 Mar 30 Mar 26 Mar 23 Mar 18 Mar 12
Last 24° Apr 20 Apr 15 Apr 12 Apr 9 Apr 7 Apr 4 Apr 1 Mar 29 Mar 25
Last 28° May 2 Apr 27 Apr 24 Apr 21 Apr 18 Apr 16 Apr 13 Apr 10 Apr 5
Last 32° May 15 May 11 May 8 May 6 May 4 May 2 Apr 30 Apr 27 Apr 23
Last 36° May 27 May 22 May 19 May 16 May 13 May 10 May 7 May 4 Apr 29

Now that you know your frost dates, use our Garden Planting Calendar for Fort Collins, Colorado to know when to sow and transplant your various vegetable plants!

Data is provided by the NOAA National Centers for Environmental Information. Photography by Garden.org member TBGDN.

Sponsored by Victory Seed Company
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