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 15, 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.
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
Last 16° | Mar 15 | Mar 7 | Mar 1 | Feb 24 | Feb 20 | Feb 15 | Feb 10 | Feb 4 | Jan 27 |
Last 20° | Mar 27 | Mar 21 | Mar 16 | Mar 12 | Mar 8 | Mar 4 | Feb 28 | Feb 23 | Feb 17 |
Last 24° | Mar 31 | Mar 27 | Mar 24 | Mar 22 | Mar 19 | Mar 17 | Mar 14 | Mar 11 | Mar 7 |
Last 28° | Apr 14 | Apr 9 | Apr 5 | Apr 2 | Mar 30 | Mar 27 | Mar 24 | Mar 21 | Mar 16 |
Last 32° | Apr 21 | Apr 18 | Apr 15 | Apr 12 | Apr 10 | Apr 8 | Apr 6 | Apr 3 | Mar 30 |
Last 36° | May 7 | May 2 | Apr 29 | Apr 26 | Apr 24 | Apr 21 | Apr 18 | Apr 15 | Apr 10 |
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° | Dec 6 | Dec 13 | Dec 18 | Dec 22 | Dec 26 | Dec 30 | Jan 3 | Jan 8 | Jan 14 |
First 20° | Nov 24 | Nov 30 | Dec 4 | Dec 7 | Dec 10 | Dec 14 | Dec 17 | Dec 21 | Dec 27 |
First 24° | Nov 8 | Nov 13 | Nov 17 | Nov 20 | Nov 23 | Nov 26 | Nov 30 | Dec 3 | Dec 9 |
First 28° | Oct 25 | Oct 31 | Nov 3 | Nov 6 | Nov 9 | Nov 12 | Nov 16 | Nov 19 | Nov 24 |
First 32° | Oct 16 | Oct 21 | Oct 24 | Oct 27 | Oct 30 | Nov 2 | Nov 5 | Nov 9 | Nov 14 |
First 36° | Oct 2 | Oct 7 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 25 | Oct 30 |
Now that you know your frost dates, use our Garden Planting Calendar for Wilmington New Castle Co Ap, DE 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.