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Chilling Hour Requirements for Fruit Trees in Oklahoma

A common lamentation from fruit tree owners: One year you will have a huge harvest (enough for you and the critters that pick through the tree), and the next you harvest barely enough to bake one pie.

For those fortunate enough to have mature fruit trees on their property, fruit production may seem confusing due to the bewildering number of factors that play a role in the setting and maturation of fruit.

One of these factors is chilling hour requirements. Chilling hours are simply a measurement of the number of hours of winter temperature below 45 degrees and above 32 degrees.Many fruit trees need a certain number of hours in this golden zone in order break dormancy and activate their fruit-growing buds.Different types of fruit and different varieties within the same type of fruit have widely different requirements for the number of chilling hours. Different varieties of peaches, for example, may require as little as 200 chilling hours or as many as 1200.

It is important to research the specific variety of fruit tree (save those labels when you are buying a new one!) and find out your chilling hour requirement. After determining the needs of your tree, you can check how many chilling hours you have had in your area. This can be accomplished by visiting Using the Get Chill website, you can put in the station id KOKNORMA27 for the Highway 9 weather station in Norman. This will give you a number of chilling hours observed by the sensors at that station between the dates you have entered.

In addition, if you are planning on planting a new fruit tree, having this information is very important and will help you choose a variety that will be best suited to your area. If the seller or nursery does not know the chilling hours of a particular fruit tree they sell, look up the variety online or find another nursery that is better informed. Chilling hour requirements are vital to fruit production and should not be left to chance! 

This Tree Tip provided by the Norman Tree Board.