One of the biggest challenges to Texas gardeners in the fall is the quick temperature swings that can catch even the most diligent weather-watchers off guard. Last week we had a beautiful warm morning and freezing temperatures by evening. I confess that I lost a potted plant to that freeze because I didn’t get it inside fast enough. Oops!
Have you ever wondered what happens to a plant when it freezes or why some plants can handle freezing temperatures better than others? We can do a lot to help our plants survive cold snaps if we understand how cold affects plants and the best ways to protect them.
Plants are made up about 90% water, which helps to regulate temperature and transport nutrients. When water inside plant cells freezes, ice crystals form that can cut the cell walls. Fluid leaks out of the cells as the temperatures rise and the cells begin to decay. You might have noticed the leaves on a plant that froze will turn dark and limp or brown and dry.
Many trees and woody plants can resist freeze damage because they go dormant in the winter, like pecan and peach trees. These plants might be injured by freeze if we get an early freeze before they have time to harden off or if we get a late freeze in the spring after they have started growing new leaves. Other woody plants like hollies can tolerate very cold temperatures.
Some herbaceous plants (non-woody) like lilies, irises, pansies, and snap dragon can withstand very cold temperatures, while other spring and summer growing herbaceous plants like begonia and coleus will be damaged at freezing temperatures. Be sure to check the cold hardiness on the plant label as you plan your landscape so you will know what can survive the cold and what will need to be protected.
When a freeze is expected in the forecast, take steps to ensure your plants are protected. Use a protective cover such as sheets, blankets, or row cover. The cover will not provide insulation, but it helps trap radiant energy rising from the ground. Plastic sheets or tarps are not an effective plant cover.
Another effective protection is to water the soil around plants before a frost or freeze. Wet soil and water will capture heat energy during the day and release it upward as temperatures freeze at night. Plants are also able to resist freezing better if they are not drought stressed. Potted plants can be moved under porches or in garages where they can be protected from wind and absorb heat from the building.
Hopefully, your plants survived the first freezes of the season, at least better than mine did! Check out the article below, “Protecting Landscapes and Horticultural Crops from Frosts and Freezes”. For more information about gardening, contact Kate Whitney, Horticulture Extension Agent for Williamson County, at 512-943-3300.
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