CHILL FACTOR

Fruit and nut trees have what is called a chilling requirement. This requirement varies between varieties within a kind of fruit. The chilling requirement for a variety is defined as the accumulation of hours below 7C. Satisfying the chilling requirement will result in normal growth and bloom following a dormant or winter period. During extremely mild winters the chilling requirement may not be met and will result in uneven bloom. The tree will remain dormant until early summer when a small shoot or several fruit will form on the end of a long naked branch. Varieties that have a chilling requirement of 450 hours or below are termed "low chill" varieties. In general, the higher the chilling requirement of a variety, the later bloom will occur in the spring.

Table. General Chilling Requirements of Various Fruits and Nuts Fruit or Nut Chilling Requirement (hours)