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 21. 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 30, 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 26 | Mar 19 | Mar 14 | Mar 9 | Mar 5 | Mar 1 | Feb 24 | Feb 19 | Feb 12 |
Last 20° | Apr 6 | Mar 31 | Mar 27 | Mar 23 | Mar 20 | Mar 17 | Mar 13 | Mar 9 | Mar 3 |
Last 24° | Apr 16 | Apr 11 | Apr 7 | Apr 3 | Mar 31 | Mar 28 | Mar 25 | Mar 21 | Mar 15 |
Last 28° | Apr 28 | Apr 23 | Apr 19 | Apr 15 | Apr 12 | Apr 9 | Apr 6 | Apr 2 | Mar 28 |
Last 32° | May 8 | May 4 | May 1 | Apr 29 | Apr 26 | Apr 24 | Apr 22 | Apr 19 | Apr 14 |
Last 36° | May 21 | May 16 | May 13 | May 11 | May 8 | May 6 | May 3 | Apr 30 | Apr 26 |
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 26 | Dec 2 | Dec 6 | Dec 10 | Dec 14 | Dec 17 | Dec 21 | Dec 25 | Dec 31 |
First 20° | Nov 9 | Nov 15 | Nov 20 | Nov 23 | Nov 27 | Dec 1 | Dec 4 | Dec 9 | Dec 15 |
First 24° | Oct 23 | Oct 29 | Nov 3 | Nov 7 | Nov 11 | Nov 15 | Nov 19 | Nov 24 | Dec 1 |
First 28° | Oct 10 | Oct 15 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 4 | Nov 9 |
First 32° | Sep 28 | Oct 4 | Oct 8 | Oct 11 | Oct 14 | Oct 18 | Oct 21 | Oct 25 | Oct 30 |
First 36° | Sep 24 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 8 | Oct 11 | Oct 14 | Oct 18 |
Now that you know your frost dates, use our Garden Planting Calendar for Lambertville, NJ 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.