The levels at which chilling hours have accumulated across the state during the most recent 10-year cycle are illustrated in Figure 1. Winter Chilling Requirements in Alabama Chilling needs vary with fruit types, but estimates of chilling requirements for the most commonly grown fruit types are listed in Table 1. The cold or chilling requirement of peach and nectarine trees, and sometimes other plants, is generally listed in the catalogs of most nurseries that sell these plants. For example, Sentinel peach is listed as having an 850-hour chilling requirement. This means that to successfully grow this variety in a particular area, it should receive an average of at least 850 hours of temperatures at or below 45 degrees F during the fall and winter period.
Most varieties have the same chilling requirement for leaf and fruit buds.
They are measured in the following way. A base temperature of 40 degrees F is subtracted from either the temperature for that hour or 77 degrees F, whichever is lower. A warm day in spring can result in 650 to 700 GDHs accumulating in 24 hours. The GDHs for each hour are totaled over time and can be used to predict the stage of development of the plant. For example, peaches usually require 10,000 to 13,000 GDHs to reach 50 percent bloom stage after rest is satisfied.