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Tree Fruit: What are chill hours?

Mississippi's winter chilling information

Deciduous fruits and nuts stop growing in late summer or fall, drop their leaves, go dormant during the winter, and then resume growth in the spring. This relationship between plant and environment is important to the survival of the plant. Growing plants that are non-hardy and incapable of becoming hardy need dormancy during winter for survival. In areas where winters may fluctuate between cold and mild temperatures, species have developed long chilling requirements, so they will not begin to grow in midwinter even though it may warm up to growing temperatures for several days.

Endodormancy (rest) is defined as that period when buds are dormant because of internal physiological blocks that prevent growth even under ideal external conditions for growth. Chilling termperatures above freezing terminate endodormancy. Chilling hours are defined as period of time between 32º F and 45º F. Plants are assigned a certain chilling requirement based on the amount of cold needed to cause 50 percent of the buds to break and flower in the spring. Most blueberries have a chilling requirement of 400-600 hours. Peaches are planted using the chilling requirement as a criteria for variety selection and range from a low of 400 to a high of 1250. Average chilling hours during the winter in Mississippi are: Hattisburg - 400-600; Jackson - 600-800; Mississippi State University - 800-1000; and Holly Springs - 1000-1200.

In 1999, middle to lower Mississippi experienced a low chilling hour accumulation. There is a material (Dormex) that can be sprayed on the commercial plantings that will substitute for about 200 hours. This material is a restricted-use pesticide and can damage the plant if used improperly. Dr. John Braswell, Dr. Frank Matta, and I have asked for, and received, a Mississippi Label for this material.

Dr. Arlie Powell (fruit specialist in Alabama) has performed research and demonstrations with Dormex in Alabama for over 10 years. Information concerning Dormex can be found on their web site, Alabama Winter Chilling

At this time, we feel that we will accumulate sufficient chilling hours in Mississippi. However, some growers may be interested in discussing the use of Dormex in late Febuary.

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A man holds pruning loppers as he stands next to a tall blueberry bush.
Filed Under: Commercial Fruit and Nuts, Fruit July 16, 2019

Pruning is a task I put off, and my blueberry bushes serve as a testament to this fact. Mainly, I am unsure how to do it correctly most of the time and don’t want to kill my plants.

Filed Under: Commercial Fruit and Nuts February 11, 2019

Commercial pecan growers can learn about orchard establishment and management during the 2019 Pecan Education Workshop March 20 in Raymond.

Filed Under: Commercial Horticulture, Commercial Fruit and Nuts January 9, 2019

Fruit and vegetable growers, or those interested in getting into the business, are invited to a daylong conference Feb. 26 in Verona.

Man leans over a 5-gallon bucket placed under a large mechanical unit inside a building.
Filed Under: Commercial Fruit and Nuts, Nuts, Fruit and Nut Diseases November 2, 2018

STARKVILLE, Miss. -- Mississippi’s pecan yields will be down from last year, but the future looks promising.

Mississippi Pecan Growers Association President Max Draughn of Raymond explained that pecan yields alternate from year to year.

Muscadines of various shades are bunched on the vine.
Filed Under: Commercial Fruit and Nuts, Fruit August 8, 2018

Producers can learn about issues related to muscadine production and other fruit-related topics at an upcoming field day in Pearl River County, south of McNeill.

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