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