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 7. 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 April 16, so we don't dare plant that early. We wait a few days and by April 24 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°||Mar 11||Mar 4||Feb 26||Feb 22||Feb 18||Feb 13||Feb 9||Feb 3||Jan 27|
|Last 20°||Mar 23||Mar 16||Mar 11||Mar 6||Mar 2||Feb 26||Feb 22||Feb 17||Feb 10|
|Last 24°||Mar 28||Mar 24||Mar 21||Mar 18||Mar 16||Mar 14||Mar 11||Mar 8||Mar 4|
|Last 28°||Apr 11||Apr 6||Apr 3||Mar 31||Mar 28||Mar 26||Mar 23||Mar 20||Mar 15|
|Last 32°||Apr 20||Apr 16||Apr 13||Apr 11||Apr 9||Apr 6||Apr 4||Apr 1||Mar 28|
|Last 36°||May 7||May 3||Apr 30||Apr 27||Apr 24||Apr 22||Apr 19||Apr 16||Apr 11|
The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:
|First 16°||Nov 27||Dec 7||Dec 13||Dec 19||Dec 25||Dec 30||Jan 5||Jan 12||Jan 21|
|First 20°||Nov 23||Nov 29||Dec 4||Dec 8||Dec 11||Dec 15||Dec 19||Dec 23||Dec 30|
|First 24°||Nov 5||Nov 12||Nov 17||Nov 21||Nov 25||Nov 29||Dec 3||Dec 8||Dec 15|
|First 28°||Oct 19||Oct 25||Oct 30||Nov 2||Nov 6||Nov 10||Nov 14||Nov 18||Nov 25|
|First 32°||Oct 12||Oct 17||Oct 21||Oct 23||Oct 26||Oct 29||Nov 1||Nov 4||Nov 9|
|First 36°||Sep 30||Oct 5||Oct 9||Oct 12||Oct 15||Oct 17||Oct 20||Oct 24||Oct 29|
Now that you know your frost dates, use our Garden Planting Calendar for Natl Arboretum Dc, MD 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.