Really Cool Information for Gardeners

Frosted sungold tomato (Nov. 11, 2007)

Whenever two gardeners chat these days, one almost always asks the question, “Have you had a frost yet?”

The temperature here at Meadow Glenn was 38°F. this morning.  I thought there were frost crystals on the roof of our house, but there were no pockets of frosty grass in the low spots of our lawn.  The leaves of the super-sensitive basil in our garden remain bright green, not the drooping black they would be if frost had kissed them good-bye.

Today is October 23, and the 10-day forecast on Weather.Com lists the lowest temperature as 42°F.  Isn’t our first freeze overdue?

The short answer is, “Yes,” but other than from daily observation and recording of temperatures, which I haven’t done, where can I find out when the first freeze will be in the fall and the last freeze will be in the spring in our neighborhood?

After years of wondering, I’ve finally found a good source.  My discovery started last Friday with a posting by the Capital Weather Gang on the Washington Post website: “When should the Washington, D.C., area expect to see its first freeze of the cold season?”

Frosted strawberry leaves (November 8, 2007)

I read their article with increasing interest and began following highlighted links.  One spreadsheet, “List of locations included in the contour map,” contained first-freeze dates for 58 locations here in Maryland—and eight in Delaware, three in New Jersey, three in Pennsylvania, 72 in Virginia, and 18 in West Virginia.

I skimmed down the Maryland list and found Clarksville and Brighton Dam, both of which are about three miles from our home.  The compilation says the average first-freeze date for both locations is October 12.  Since today is October 23, yes, our first freeze is late this year.

The Capital Weather Gang explained that the first-freeze metric is “tricky … and it’s often first elevation dependent, then later (November onwards) dependent on the strength of the cold air mass, and in many cases one’s proximity to water.”

I’d like to add another complication: First-frost may come before first-freeze.  How can that be?   I noticed several years ago that frost often forms in our garden when the official temperature is above freezing by a degree or two.  When I researched that issue, I found that the thermometers used to officially record temperatures generally are located about six feet above ground.  Under certain conditions, the temperature at ground level can be freezing while the official temperature is slightly warmer just a few feet above.

 If you are a curious gardener, I recommend that you read the Capital Weather Gang’s posting, and I even more strongly urge you to follow the link to “weather cooperatives through the broader region,” which takes you to the Utah State University website with historical weather information.  When you arrive at the site, you’ll find “Utah” in the box where you are to select a state.  Select Maryland, or another state, from the pull-down list and click Select again, and you’ll find great information for scores of locations.  There are early/average/late dates for both “last spring freeze” and “first fall freeze,” plus short/average/long “freeze-free days,” which you might call the “growing season.”

Here are the dates for our town, Clarksville: “last freeze,” April 14 early, May 4 average, May 22 late.  “First freeze,” Sept. 24 early, Oct. 12 average, Nov. 5 late.  “Freeze-free days,” 138 short, 161 average, 188 long.   I can use that information, for example, to help determine when to start seeds indoors or plant them in the garden—and for spicing up gardening chats: “Well, you know, [clear throat at this point] on the average we should have had a frost on the twelfth.”

Now it’s time for you to explore. To link to the Capital Weather Gang’s posting, CLICK HERE.  To link to the Utah State University site to check out spring and fall freeze dates for your town, CLICK HERE.