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 2, so we don't dare plant that early. We wait a few days and by May 12 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.
|Last 16°||Apr 9||Apr 1||Mar 27||Mar 22||Mar 18||Mar 13||Mar 9||Mar 3||Feb 24|
|Last 20°||Apr 15||Apr 9||Apr 5||Apr 2||Mar 30||Mar 27||Mar 23||Mar 20||Mar 14|
|Last 24°||Apr 27||Apr 21||Apr 16||Apr 12||Apr 9||Apr 5||Apr 2||Mar 28||Mar 22|
|Last 28°||May 7||May 1||Apr 27||Apr 23||Apr 20||Apr 17||Apr 13||Apr 9||Apr 3|
|Last 32°||May 13||May 9||May 5||May 2||Apr 30||Apr 27||Apr 24||Apr 21||Apr 16|
|Last 36°||May 27||May 22||May 18||May 15||May 12||May 9||May 6||May 2||Apr 27|
The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:
|First 16°||Oct 30||Nov 4||Nov 8||Nov 11||Nov 14||Nov 16||Nov 19||Nov 23||Nov 28|
|First 20°||Oct 17||Oct 23||Oct 27||Oct 31||Nov 3||Nov 6||Nov 10||Nov 14||Nov 20|
|First 24°||Oct 10||Oct 16||Oct 20||Oct 24||Oct 28||Oct 31||Nov 4||Nov 8||Nov 14|
|First 28°||Sep 28||Oct 4||Oct 8||Oct 11||Oct 15||Oct 18||Oct 22||Oct 26||Nov 1|
|First 32°||Sep 18||Sep 24||Sep 28||Oct 1||Oct 4||Oct 8||Oct 11||Oct 15||Oct 21|
|First 36°||Sep 15||Sep 19||Sep 22||Sep 24||Sep 27||Sep 29||Oct 1||Oct 4||Oct 9|
Now that you know your frost dates, use our Garden Planting Calendar for Denver, Colorado to know when to sow and transplant your various vegetable plants!