Chill Hours

A Benefit to the Winter Blues: Chill Hours

Cold temperatures arrived in Williamson County in a hurry this year! I hope were able to cover your plants to protect them from the freezing temperatures.  I have to admit that I am a summer lover and I really do not like the short daylight hours and cold temperatures of winter.  There is one bright side to the cold: a winter with enough cold hours makes for a good summer crop of peaches!

Many of our favorite summer fruits like peaches, plums, and nectarines require a certain number of hours of cold weather, called chill hours. Chill hours are temperatures between 32◦ and 45◦F. In the late fall and early winter, fruit trees go into dormancy and hormones within the plant suppress the bud until temperatures warm up and the days lengthen in the spring.  The hormone that causes the plant to go into dormancy breaks down in the temperature range of chill hours.  In an ideal winter, the hormone has enough child hours to completely break down by the time spring comes around and the tree needs to begin blooming.  What a cool process!

In Texas, you might have noticed that the weather is unpredictable. In some winters we do not get enough chill hours for our fruit trees.  This can cause delayed foliation and the tree does not set much fruit.  Some winters we get a late freeze after the trees have bloomed and the blooms do not set fruit.  It’s a challenge, but well worth it when we get a good crop!

Williamson County usually receives between 450-750 chill hours each year. You can do a few things at your home to help ensure that you get some fruit every year.  Purchase varieties of fruit trees that need the recommended number of chill hours for our area.  In peaches, you can get Flordaking, Rio Grande, and Texstar varieties which need 450 hours.  La Feliciana, Junegold and Texroyal need 550-600 chill hours.  Another trick is to purchase several varieties with varying chill hours so you have a better chance that one variety will get the right number.

If you are mourning the loss of your tomato and basil plants after the recent freeze, take heart, the peaches are coming! For more information about growing fruit trees and chill hours, visit the Aggie Horticulture website at or contact Kate Whitney, Williamson County Horticulture Extension Agent, at

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