Native to the temperate climate of eastern Asia, Japanese maples (Acer palmatum) appreciate a long, warm growing season but do not perform their best in excessive heat. Warm nighttime temperatures on maple trees can lead to fungal diseases and reduced metabolism. A chilly winter dormancy is also required for this species, which is best in USDA Hardiness Zones 5 through 8.
The beginning of the growing season for a Japanese maple is the last frost date, the last time the temperature reaches or drops below 32 degree Fahrenheit in spring. Once the growing season starts, nighttime temperatures for Japanese maples only need to remain above the freezing point to prevent damage or loss to emerging and maturing leaves. A gradual warming trend in spring is best, but the maple does not falter during the transitional spring weather and temperatures as long as soil remains moist.
Many varieties of Japanese maples tout a "better heat tolerance", which refers to the plant's performance in the prolonged, hot summers of the American South, for example. However, this heat tolerance limits the tree's ability to grow in summer if there is not at least a 10 to 15 degree Fahrenheit drop in temperature between daily high and low temperatures. Occasional nighttime temperatures in the 70 to 80 degree range are not detrimental to Japanese maples, but if the climate overall is hot and nighttime temperatures fail to drop below 75 degrees, plant metabolism is disrupted. As a general rule, even if summer high temperatures are over 85 degrees, if nighttime temperatures drop at least 15 degrees overnight, to 70 degrees or lower, the overall health and growth of a Japanese maple remains strong. This helps explain why Japanese maples do not endure in hot summer regions like central and southern Florida.
In the autumn, growth of the Japanese maple slows as day length shortens and nighttime temperatures gradually approach freezing. This plant tolerates frost without harm, but an initial frost or freeze in autumn can cause leaf drop without the usual ornamental leaf color change to red and orange. Nighttime temperatures in the range of 20 to 50 degrees naturally allow the maple to assimilate and prepare for its annual dormancy.
Japanese maples need a prolonged dormancy with temperatures below 40 degrees Fahrenheit to remain perennial. Once void of foliage and in dormancy, the tissues of maple twigs and roots survive winter nighttime lows anywhere from the -20 to 40 degree Fahrenheit range for months. The cold air and soil temperatures along with the short days and weak sunlight prevent the maples from breaking their dormancy prematurely.