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 10. 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 21, so we don't dare plant that early. We wait a few days and by April 28 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 17 | Mar 9 | Mar 4 | Feb 27 | Feb 23 | Feb 18 | Feb 13 | Feb 8 | Jan 31 |
Last 20° | Mar 30 | Mar 23 | Mar 17 | Mar 13 | Mar 8 | Mar 4 | Feb 27 | Feb 22 | Feb 14 |
Last 24° | Apr 3 | Mar 30 | Mar 27 | Mar 24 | Mar 21 | Mar 18 | Mar 15 | Mar 12 | Mar 7 |
Last 28° | Apr 17 | Apr 12 | Apr 8 | Apr 5 | Apr 3 | Mar 31 | Mar 28 | Mar 24 | Mar 19 |
Last 32° | May 3 | Apr 28 | Apr 24 | Apr 21 | Apr 18 | Apr 15 | Apr 12 | Apr 8 | Apr 3 |
Last 36° | May 10 | May 6 | May 3 | May 1 | Apr 28 | Apr 26 | Apr 24 | Apr 21 | Apr 17 |
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 28 | Dec 5 | Dec 10 | Dec 14 | Dec 17 | Dec 21 | Dec 25 | Dec 30 | Jan 6 |
First 20° | Nov 13 | Nov 21 | Nov 26 | Dec 1 | Dec 5 | Dec 9 | Dec 14 | Dec 19 | Dec 26 |
First 24° | Oct 31 | Nov 6 | Nov 10 | Nov 14 | Nov 18 | Nov 22 | Nov 25 | Nov 30 | Dec 6 |
First 28° | Oct 22 | Oct 28 | Nov 1 | Nov 4 | Nov 8 | Nov 11 | Nov 14 | Nov 18 | Nov 24 |
First 32° | Oct 10 | Oct 15 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Nov 1 | Nov 4 | Nov 10 |
First 36° | Oct 1 | Oct 6 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 23 | Oct 26 | Oct 31 |
Now that you know your frost dates, use our Garden Planting Calendar for Conowingo Dam, 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.