Preventing, preparing for freeze

Published 6:00 am Sunday, March 3, 2019

Terry Rector

February exited with my few peach trees in full bloom. The good news is bumble bees were moving pollen around amongst the blooms.  The bad news is the next few nights’ temperature might make it all for naught. 

The downside of spring weather in late winter is some plants respond by blooming early.  Then when the weather goes back to normal for the time of year, the too-early blooms and fruiting structures might freeze. And there won’t be any more to replace them. 

Perennial plants, including landscape shrubs, scheduled to bloom in early spring formed their bloom buds last summer. Now, just because the “announced” temperature drops below 32 degrees does not necessarily mean all is lost.  For one thing, overnight temperature can vary a few degrees within a relatively small area. 

Email newsletter signup

Sign up for The Vicksburg Post's free newsletters

Check which newsletters you would like to receive
  • Vicksburg News: Sent daily at 5 am
  • Vicksburg Sports: Sent daily at 10 am
  • Vicksburg Living: Sent on 15th of each month

One of the do-nots of growing your own fruit is to not plant trees, bushes or vines in a low area. That’s because cold air is heavy and will sink to the low areas, making those spots more prone to freeze damage. 

Also, adjacent forests or buildings can make a slight difference in air temperature, especially if they are to the north.

Another thing to keep in mind is the location of the thermometer. The air is coldest right at ground level during the night. A thermometer located at eye level might be read a tad higher, so bloom location on a plant can matter in a close call freeze.

The most common references to threatening low temperatures this time of year are last frost date and last freeze date. Practically, the two are used to mean the same thing; the last day of the year that the temperature reaches 32 degrees or lower. That’s even though there can certainly be a freeze without frost. 

The term killing frost is a more or less colloquial way of identifying a temperature so low it is almost guaranteed to kill emerged tender spring vegetation. I’ve read descriptions of killing frost as “below 28 degrees” for a certain minimum time period as well as “in the mid-20s.”

While moisture on the surface of a leaf or bloom will freeze at 32 degrees, moisture inside plant parts have a little insulated protection. That’s why it actually takes temperatures below freezing and time to destroy buds, blooms and fruit structures. 

For instance, people in the know about such tell us it takes four hours below 29 degrees to lose a peach crop to the cold.

Centuries of farming and gardening have produced various methods to prevent losses to freezes. Covering plants is an attempt to hold in a bit of the daytime heat absorbed by plants and the ground. Fans, wind machines and helicopters push warmer air around to replace the colder air nearer the ground. And, odd as it might seem, sprinkling water on plants to prevent loss to freeze works because the actual freezing of water generates a bit of fusion heat. All of these methods are used but provide just a few degrees of protection. 


Terry Rector is spokesman for the Warren County Soil and Water Conservation District.