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chilling hours
How many chilling hours do we get?
We get lots of questions about "chilling hours" -- the number of hours between 32F and 45F that deciduous fruit trees need in order to break dormancy and flower properly. You will often see the number of hours that a particular variety needs printed right on the label; e.g., Elberta Peach 800 hours. Gardeners in the Bay Area and Southern California may not get sufficient chilling for many varieties, and need to inquire locally about which are recommended for their area. I've attached an image showing the trend in chilling for Davis, Ca since 1996 (click to enlarge).
Note that the first year shown (1995-96) was unusually low. Chilling hours in the Davis area typically range from 800 - 1000, allowing us to grow nearly any fruit variety available.
For the chilling hours in
your
area, check this website which shows weather stations all over California:
http://fruitsandnuts.ucdavis.edu/chillcalc/index1.htm
In recent years research has focused on chilling portions as more accurate predictors of fruit set than chilling hours. This approach accounts for unusually high temperatures during the dormant season. For more information, see the articles at the same site here:
Chilling accumulation information
We still use chilling hours as a reasonable guide to which varieties will perform well in the region. Here is a chart showing some chilling hours for various fruit types and varieties:
