Smith County Horticulturist
Some can withstand prolonged spells of below freezing temperatures, while others bite the dust with only a slight exposure to a freeze.
A couple of principles should be kept in mind when trying to protect marginally hardy plants from cold, or to extend the tomato or pepper harvest by covering plants.
First, plants do not generate their own heat. So, any warmth absorbed from the energy of the sun will be quickly dissipated after a few hours of below freezing temperatures, especially if it is windy.
The most practical type of plant protection is from a radiation-type freeze. This happens on a still, cloudless night after a sunny day when plants and other surfaces release back into the atmosphere any heat energy absorbed from the sun during the day.
Overhead branches and the eves of a house can trap some of this escaping heat, creating a mini-environment that is a couple of degrees warmer than just a few feet away in the open.
Floating row covers are commercially available for covering rows of vegetables. These are lightweight, spun fabrics that give a few degrees of protection, while still letting in light and air.
If you use plastic to cover plants, be sure to support the plastic to prevent the leaves from touching the plastic, or they will burn.
The other common type of freeze happens when a strong cold front brings windy conditions, blowing away accumulated heat, and bringing plants and all other surfaces down to the surrounding air temperature.
In this case, overhangs, porches, and plants under covers all reach the same, cold temperature.
Plants that are typically hardy when planted in the ground are more easily damaged when grown in aboveground containers because the roots are more exposed to freezing temperatures. Marginally hardy plants should be moved into protected areas, such as a garage, if a severe cold event is predicted.
I knew a person who grew citrus trees in very large pots. He had scrounged for old, discarded push lawn mowers.
He removed the engines, leaving the deck, wheels and handle for a convenient cart to move his heavy potted plants in and out of the garage during the winter.
Historical weather data for East Texas – dating as far back as the 1960s for some items – is only a mouse click away on the Internet.
Located at http://etweather.tamu.edu, the site lists daily weather data for rainfall, maximum temperature, minimum temperature, average temperature and total monthly rainfall back to January 1995.
There are actually lots of interesting data on this site, including a handy chart that lists dates and temperatures of the first freezes at Overton for the last 14 years.
The earliest in this time period was Oct. 28 in 2008, and the latest first freeze was the following year on Dec. 3, 2009.
Overton temperatures tend to be a few degrees lower than in the city of Tyler.
Also located on this web site are historical rainfall data, and accumulated chilling hours, of interest to fruit growers in this area.
Keith Hansen is Smith County Horticulturist with the Texas A&M AgriLife Extension Service. His web page is EastTexasGardening.tamu.edu His Blog is agrilife.org/etg.