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Climate
The orange is subtropical, not tropical. During the growing period, the temperature should range from 55� to 100� F (12.78�-37.78� C). In the winter dormancy, the ideal temperature range is 35� to 50� F (1.67�-10� C). Mature, dormant trees have survived 10 hours at temperatures below 25� F (-3.89� C) but fruit is damaged by freezing�30� to 26� F (-1.11�-3.33� C). Young trees may be killed outright by even brief frosts. Hardiness, however, varies with the cultivar and rootstock, Seedling orange trees of bearing age are capable of enduring more cold than budded cultivars. Prolonged cold is more injurious than short periods of freezing temperatures. In Florida, many efforts have been made to protect orange trees from winter cold, which is most damaging if preceded or accompanied by drought.
In the early days, slatted shadehouses were erected over young groves. Windbreaks have been planted on the northeast exposure. Old automobile tires have been burned in piles throughout groves. A commercially produced heater has been fueled and lit in the coldest predawn hours. Helicopters have been flown back and forth to cause movement of air, and, more recently, wind machines have been installed. Most recent, and most effective are overhead sprinklers which give maximum protection from cold damage.
Favorable annual precipitation varies from 5 to 20 in (12.5-50 cm), though oranges are frequently grown in areas receiving 40 to 60 in (100-150 cm) of rain. Benthall says that in the damp climate of Lower Bengal, the fruits lack juice and are usually very sour. California's generally dry climate contributes to more intense color in the orange peel than is seen in humid areas. Success in orange culture depends a great deal on the selection of cultivars tolerant of the weather conditions where they are to be grown.