Frost Update for Fruit and Vegetable Growers 5/6/2020

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There is a possibility of a frost event this weekend in Northeastern NC. Growers can use this table, provided by Georgia Cooperative Extension (GCE), to determine the risk level in their area. The table allows you to determine what the wet-bulb temperature will be. The wet-bulb temperature measures the lowest temperature that can be reached from water evaporating into the air. Dew-point temperatures

For example, using this graph from the National Weather Service for Tyner, NC, the low on Sunday morning is projected to be 38° F with a dewpoint of 32°. According to the GCE table, a freeze event should not happen.

Chart

For many growers with plants already in the ground, row covers will offer frost protection, but they are only practical on a small scale. Overhead irrigation can also be used, but plants must be irrigated continuously. Because of this, center pivots and traveling guns do not offer protection. Keep in mind that sandier soils have more and larger air pockets that allow water to evaporate and drain faster. This means that heat energy will be lost at a higher rate. Plants grown on black plastic have better protection from frosts because they have the ability to absorb and trap heat. In one study conducted in Georgia, a 2° Fahrenheit increase in minimum temperature was observed in watermelons on black plastic compared to bare ground plants during a freeze event.

Growers in areas of high risk are encouraged to hold off on fertilizing until after the cold snap. This will help keep plants more hardened as fertilizer applications encourage plants to put on tender new growth. Cultivation should also be avoided until after this weekend. Breaking up soil creates more air space that allows cold to penetrate during a frost event. Most importantly, if you are a grower in a high-risk area, planting of sensitive transplants should be held off until temperatures rise.

For more information on frost and frost protection for fruits and vegetables, contact Nettie Baugher at nettie_baugher@ncsu.edu.