Chilling Requirement for Fruit and Nut Trees

Published: February 1, 2010

Are you sick and tired of this cold dreary weather? While we may long for a sunny beach at this time of year, this is perfect weather for fruit and nut trees. These trees require a period of low temperatures in the range of 32 and 40ºF during winter to produce flowers and fruit later in the growing season. The number of hours necessary to fulfill the chilling requirement varies among fruit crops and cultivars. Strawberries only require about 200 hours of chilling so they can be grown in warm areas like Florida and California. Low-chill blueberry, blackberry, peach, and apple cultivars have also been developed to fruit in warmer climates. However, peach, plum, cherry, and apple trees grown in Missouri generally need 800 to 1200 hours of chilling temperatures. Black walnut trees have a long chilling requirement of more than 1400 hours. Because of the long chilling period, walnuts are one of the last trees to break bud and start growing in spring.

While many of us enjoy days in February and March when the temperature rises above 60, this is not good for fruit trees that have already fulfilled their chilling requirement. With warm temperatures, fruit buds deacclimate rapidly. After this occurs, fruit buds can be damaged when the temperatures quickly drop below freezing. In Missouri, erratic temperatures in February or March frequently cause some fruit bud injury. Unfortunately, the closer we get to spring, fruit buds become more susceptible to frost injury. The greatest potential for injury occurs when we get a frost or freeze and the trees are in full bloom. In spite of the low temperatures, only 5 to 10% of the fruit buds on a tree are necessary to produce a full crop. So for now, take a trip to a warm sunny spot and leave the fruit and nut trees behind in the cold winter weather!