A chill hour, or chill unit, is an hour of time during which the temperature is between 32 degrees F and 45 degrees F. Most fruit trees and certain flowers require a minimum number of chill hours to go dormant so they will develop flower buds the following spring. Too few chilling hours will cause poor to no fruit the following year. Temperatures below 32 degrees F do not count toward chill hours and can be harmful if the temperature remains below freezing for much of the winter.

Chill hours can vary greatly depending on the location, elevation, and year. This makes it difficult to find accurate information on the number of chill hours in an area. In the past there have been websites that helped to calculate chill hours, but they are no longer available. Most of the information available indicates that the Willamette Valley gets more than 1400 chill hours a year. Chill Hours – HARVESTRY is a site you can look at, however its reliability is uncertain.

Most fruit trees require between 200 and 1,000 chill hours to break dormancy. Temperatures in the Willamette Valley are cold enough during a normal winter to receive sufficient chilling for all deciduous fruit trees and are therefore not an issue in this part of Oregon. This website has more information about the Chill Hours required for a variety of fruit trees: Chill Hours by Zip Code — Free Calculator for Fruit Trees | Leaftide

This site will provide you with more general information on choosing fruit trees for your garden: Growing tree fruits and nuts at home | OSU Extension Service

Good luck with your fruit trees!