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 22. 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 29, so we don't dare plant that early. We wait a few days and by May 8 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.
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
Last 16° | Mar 27 | Mar 23 | Mar 19 | Mar 16 | Mar 14 | Mar 11 | Mar 8 | Mar 5 | Feb 28 |
Last 20° | Mar 31 | Mar 27 | Mar 24 | Mar 22 | Mar 20 | Mar 18 | Mar 15 | Mar 13 | Mar 9 |
Last 24° | Apr 10 | Apr 5 | Apr 2 | Mar 30 | Mar 28 | Mar 26 | Mar 23 | Mar 20 | Mar 15 |
Last 28° | Apr 22 | Apr 18 | Apr 15 | Apr 12 | Apr 10 | Apr 8 | Apr 5 | Apr 2 | Mar 29 |
Last 32° | May 10 | May 5 | May 2 | Apr 29 | Apr 26 | Apr 23 | Apr 20 | Apr 16 | Apr 11 |
Last 36° | May 22 | May 17 | May 14 | May 11 | May 8 | May 5 | May 2 | Apr 29 | Apr 24 |
The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
First 16° | Nov 20 | Nov 25 | Nov 28 | Dec 1 | Dec 4 | Dec 7 | Dec 10 | Dec 13 | Dec 18 |
First 20° | Nov 2 | Nov 9 | Nov 14 | Nov 18 | Nov 22 | Nov 26 | Dec 1 | Dec 6 | Dec 13 |
First 24° | Oct 20 | Oct 26 | Oct 31 | Nov 4 | Nov 8 | Nov 12 | Nov 16 | Nov 21 | Nov 27 |
First 28° | Oct 8 | Oct 13 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Oct 29 | Nov 2 | Nov 7 |
First 32° | Sep 26 | Oct 1 | Oct 4 | Oct 7 | Oct 9 | Oct 12 | Oct 14 | Oct 17 | Oct 22 |
First 36° | Sep 19 | Sep 23 | Sep 26 | Sep 28 | Sep 30 | Oct 3 | Oct 5 | Oct 8 | Oct 12 |
Now that you know your frost dates, use our Garden Planting Calendar for Hartford, CT 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.