Native to Asia Minor and North Africa, almond trees (Prunus dulcis) are closely related to peach trees. Rather than producing a sweet, juicy flesh around a pit, almond fruits are hard-shelled with a dry pit inside. Almond trees are nearly as cold-tolerant as peach trees but need milder temperatures in winter and drier, hotter summers to effectively yield nut crops.
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Almond trees are not particularly cold-hardy, but they must grow in a region with distinct, cool winters. Grow them in U.S. Department of Agriculture plant hardiness zones 7b through 10. In these areas, winter low temperatures range from 10 to 40 degrees Fahrenheit. Prolonged exposure to subfreezing temperatures over several weeks causes branch die-back and flower buds to die, especially at temperatures colder than 5 degrees.
Dormant almond trees must be exposed to at least 300 chilling hours of temperatures between 32 and 45 degrees Fahrenheit. This exposure to cold allows plants to break dormancy in the warm days of late winter to bloom; without ample chilling flowering will not occur or will be greatly reduced. The low chilling requirement of almond trees means they tend to swell their flower buds and bloom in late January or February. Often frosts still occur during that time and can kill the flower buds.
Almond Growing Regions
The greatest concentration of almond orchards in the United States is in the Central Valley of California. The winters here are cool to chilly but rarely colder than 15 degrees. Late winter is mild but often the flowers escape frosts in February and allow honeybees to pollinate blossoms and yield almond nuts later that summer. Almonds also grow well in the low and intermediate deserts of Arizona and in the mountains in southern California. Almonds can grow in Texas and Oklahoma in the more arid western counties.
Almond trees can survive in a vast southern portion of the United States where winters are mild, but the extent of winter cold and likelihood of frosts and freezes from January to March limits the range where flower and nut production occur. Perhaps more importantly for nut-production is a long, hot and rain-free summer. Cool summers or humid, wet summers both prevent almond nuts from maturing on trees.