Palms are indigenous to all continents except Antarctica and are evergreen plants. Their diversity is highest in wet, humid tropical regions. About 2,500 species of palms exist, and a few of them are quite tolerant of winter cold. Depending on species and winter weather, palm leaves or fronds often die in the drier and cooler winter temperatures. Keep in mind that in tropical regions, the winter is more of a cool, frost-free dry season, while in temperate zones, the winter brings distinctly subfreezing conditions.
With large persistent leaves and trunks lacking thick, protective bark, palms are poorly adapted to survive winter cold compared to temperate-zone trees like deciduous oaks and evergreen spruces. Each palm species tolerates a certain temperature threshold before its foliage is damaged or fully killed by subfreezing temperatures. If the soil conditions in winter aren't ideal, that can also lead to a palm becoming stressed or sickened and result in abortion of leaves. Often the colder the temperatures in winter, the drier the soil needs to be in order to discourage root rot diseases.
Palms grow from growing tips only on the top of their trunks. Sometimes the growing tip is large and elongated and called a crownshaft. If winter cold kills the existing fronds in the palm's canopy, the palm may still remain alive if the growing tip or crownshaft isn't damaged or killed. If the tip survives the winter cold, new leaves emerge in spring or summer once it's warm enough. Palms do not naturally shed their leaves in fall or winter like temperate-zone trees and shrubs.
A few upright palms demonstrate considerable tolerance to subfreezing temperatures and retain their leaves. These cold-hardy palms survive varying winter temperatures that drop into the 10 to 25 degrees Fahrenheit range, correlating to U.S. Department of Agriculture plant hardiness zones 7b through 9a. Pindo palm (Butia capitata), windmill palms (Trachycarpus spp.), cabbage palm (Sabal palmetto), European fan palm (Chamaerops humilis), hardy bamboo palm (Chamaedorea microspadix), Chilean wine palm (Jubaea chilensis), date palms (Phoenix spp.), desert fan palms (Washingtonia spp.) and the mazari palm (Nannorrhops ritchiana) do not lose their fronds unless temperatures remain under 10 degrees Fahrenheit for a prolonged period. This list is not exhaustive.
Consider most palms to be intolerant of subfreezing temperatures and their fronds to begin browning when temperatures drop below 40 degrees Fahrenheit and die once below 32 degrees Fahrenheit. Accordingly, gardeners plant most palms outdoors only in U.S. Department of Agriculture plant hardiness zones 9b and warmer. Only in these frost-free or light-frost areas do classic tropical trees like the coconut (Cocos nucifera) or royal (Roystonea regia) palms survive and not experience dead fronds from winter cold.