Chilling in the Garden

The other day, I was thinking about possible additions to my front-yard orchard. Last spring I planted two Grenada pomegranate trees and a Celestial fig tree, and this past fall I planted an All-in-One almond tree. After considering the climate I live in, I thought pears might be nice. So, I went to the website of my preferred nursery, Willis Orchards, and looked at all the pear trees they offer. I already knew that certain fruit and nut trees won’t grow in my area, but now I know the reason why.

I learned it has to do with the tree’s chill hour requirement. When fruit and nut trees become dormant in the fall, they require a certain number of chill hours before they can be coaxed out of dormancy and blossom. The definition and calculation of chill hours can get rather complicated, but basically, one chill hour equals a temperature between 32 and 45 degrees Fahrenheit for one hour between mid-November and February. This requirement must be met in order for the tree to produce fruit properly.

For example, in my area, we get an average of 400-600 chill hours. If I were to get a fruit or nut tree that required only 100 chill hours (a lot less than what my area gets), I would risk the tree blooming too early and the buds being killed by a frost. If I were to get a fruit or nut tree that required 1,000 chill hours, the tree wouldn’t reach its minimum chill hours and it would bear little to no fruit.

Early flowering varieties are best in warmer climates, like mine. Late flowering varieties are best in cooler climates. Also, early ripening varieties are best in areas with intense summers (yes…like mine!), whereas late ripening varieties are best in areas with cooler summers (I wish!). This is just a general guide; to be sure, you should talk to someone at your local nursery or your local college cooperative extension.

Now that I’m armed with this chilling information, I’m going to check out those pear trees.

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