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 June 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 May 18, so we don't dare plant that early. We wait a few days and by May 31 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° | Feb 9 | Jan 26 | Jan 14 | Jan 2 | Dec 18 | -- | -- | -- | -- |
Last 20° | Mar 1 | Feb 16 | Feb 7 | Jan 30 | Jan 22 | Jan 14 | Jan 6 | Dec 26 | Dec 5 |
Last 24° | Mar 17 | Mar 10 | Mar 5 | Mar 1 | Feb 25 | Feb 21 | Feb 16 | Feb 11 | Feb 4 |
Last 28° | Apr 20 | Apr 12 | Apr 7 | Apr 2 | Mar 28 | Mar 24 | Mar 19 | Mar 13 | Mar 5 |
Last 32° | May 31 | May 25 | May 20 | May 15 | May 12 | May 8 | May 4 | Apr 29 | Apr 22 |
Last 36° | Jun 21 | Jun 14 | Jun 9 | Jun 4 | May 31 | May 27 | May 23 | May 18 | May 11 |
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 1 | Dec 19 | Jan 2 | Jan 18 | Feb 8 | -- | -- | -- | -- |
First 20° | Nov 10 | Nov 20 | Nov 28 | Dec 4 | Dec 10 | Dec 17 | Dec 23 | Jan 1 | Jan 18 |
First 24° | Oct 18 | Oct 29 | Nov 6 | Nov 13 | Nov 19 | Nov 25 | Dec 2 | Dec 10 | Dec 21 |
First 28° | Oct 7 | Oct 13 | Oct 18 | Oct 22 | Oct 26 | Oct 30 | Nov 3 | Nov 8 | Nov 14 |
First 32° | Sep 15 | Sep 21 | Sep 26 | Sep 29 | Oct 3 | Oct 6 | Oct 10 | Oct 14 | Oct 20 |
First 36° | Sep 3 | Sep 10 | Sep 14 | Sep 18 | Sep 21 | Sep 25 | Sep 29 | Oct 3 | Oct 9 |
Now that you know your frost dates, use our Garden Planting Calendar for Medford, OR 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.