Have we had our last frost?
Oh how these recent sunny days whet the appetite for spring gardening! As I write this, I am encased in my office at a computer wishing I could be outside. My window has a smudge where I press my nose to the glass waiting for the weekend.
As you read this in early March, there has been one consistent question that I have been hearing, “Have we had our last frost?”
This question (and its answer) can be simplified to one date, but requires an abundance of history, statistics and science that I’ll sum up here:
Simply stated, March 13 is the “average” last day to see a frost.
The average gives us a historical mid-point, an average of the dates that did reach down to 32 degrees F. Thus on March 13 we have a 50-50 chance of it reaching that temperature. Historically, last Friday, March 4 we would have expected a 70% chance of seeing another frost. Hmm….
If that concerns you, remember that a “frost” is not a “freeze”. Water freezes at 32 degrees F – that would be a frost. Water in a solution (such as the water contained in flower buds) requires a lower temperature.
For peaches, temperatures at or below 28°degrees F for 30 minutes or more will cause commercially important damage to a developing peach crop. Temperatures of 25°degrees F or below will generally cause severe damage to the peach crop. For blueberries, open blueberry blossoms and green fruit will freeze at 29 degrees F.
Freezes at or before the swollen bud stage are generally not an important problem, though one can bet that it sure causes an enormous level of stress for growers watching the thermometer during those really cold spells.
Vegetable gardeners know too well that onions can take a colder temperatures, but tomatoes (and other warm climate vegetables) will perish and have to be replaced.
Now many out there will be saying, “But when is Easter? That’s what I base my planting dates on.”
Easter this year is on Sunday, March 27. Historically, again, Easter can be as early as March 22 and as late as April 25.
In the year 325, an early Christian council determined that Easter would be held on the first Sunday after the first full moon occurring on or after the vernal (spring) equinox. An equinox is the midpoint between the summer and winter solstice. A solstice typically equates as the longest and shortest days of the year. Regarding the reference to the moon, we have a full moon every 29-30 days.
The moon’s rotation around the earth isn’t on the same time frame as the earth around the sun. The result? Nearly a month of difference between the earliest and latest dates for Easter.
Now with all the talk about the historical averages, frosts vs. freezes, Easter and the lunar phases aside, have we seen our last frost?
I have no idea. Looking at a 15 day forecast (from the time this article was written), the middle of March looks to have a high of 84 degrees F and a low of 56 degrees F.
Maybe I’ll just wait until after my pecans bud out…
Cary Sims is the County Extension Agent for agriculture and natural resources for Angelina County. His email address is email@example.com.