Chill hours measure exposure to cool winter temperatures (hours are the number of hours below 40°F in the winter) that help certain fruit trees complete dormancy and resume normal growth and flowering in spring. Chill requirements vary by species and variety, and different calculation models are used. A lack of chill hours is generally only a problem for very warm areas, such as Florida.

Selecting a variety with chill requirements suited to your local climate can improve flowering and fruit production, especially in warmer growing regions.