Chilling hours are one of the important things to consider before planting any fruit-bearing tree.  There are at least a couple of ways to calculate chilling hours, and I will discuss them below.  Oversimplified, chilling hours are the number of hours the buds on the tree are cold enough to remain dormant.  If the buds are not dormant long enough, the fruit does not develop right and your crop is either absent or severely curtailed.

Why Chilling Hours Are Important

Take peaches, for example.  All peaches need at least 200 chilling hours to set fruit.  Some varieties need as much as 1000 hours.  So if you plant an 800-hour peach tree in a 400-hour climate, you would never get any fruit.  This works, to some extent, in reverse, too.  A 400-hour tree planted in an 800-hour area will tree to bud out too early and the blossoms will freeze.  So no fruit there, either.

How To Calculate

Your county extension office can tell you how many chilling hours your county gets.  In Texas, Texas A&M publishes chilling hours each year.  The calculations are done several ways, but the most common two are 1)to calculate the number of hours between 32 -45 F from October 1 through February 28th and 2)to calculate the number of hours under 45 F from October 1 through February 28th.  The difference is that method one may account for the harmful effects of severe cold on the buds.  Fights have broken out over which of these methods is best, but both will give you an idea of what figures to use.

Match Tree And Chilling Hours

Different varieties of peaches need different numbers of chilling hours.  All stone fruit varies, but it is an important factor in growing them successfully.  Symptoms of insufficient chilling hours are delayed foliage, reduced fruit set and buttoning, and reduced fruit quality.  When deciding on a variety of fruit trees, make sure you pick one that matches the necessary chilling hours for your area.

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