Deciduous fruits and nuts drop their leaves and produce new leaves and flowers in response to temperature. The temperature to which they respond is measured in chilling hours. For use in selecting fruit varieties we count each hour below 45 degrees F as a chilling hour. If a deciduous fruit plant has not been exposed to the required number of chilling by the time it is warm enough for leaves and flowers to function properly in the spring, the development of leaves and flowers will be so delayed that fruit production will not be acceptable.
The Piru area receives on average 456 chilling hours, while the Pt. Hueneme area averages 191 chilling hours.