It's normal for palm trees (Arecaceae family) to go dormant when the weather turns cool. The dormancy period varies by climate, generally beginning in the autumn and extending through winter until the temperatures become warm again. Palm trees grow outdoors in U.S. Department of Agriculture plant hardiness zones 9 to 10, although hardiness varies by species. Many types of palm tree also grow as houseplants.
Palm trees differ from most trees in that they grow only from the crown, making them particularly vulnerable to damage from freezing. Palm trees rely on their fronds for some of their nutrient needs, so if there's damage, don't remove fronds unless they are entirely brown. Palm tree seeds remain inert, storing the food needed for the palm to begin its life, until the right conditions occur. The seed requires enough warmth and moisture to sustain life before it will germinate.
Dormancy is to trees what hibernation is to animals. Palm trees generally become dormant in cool weather, such as from late fall through winter. This means its growth slows or stops until warm weather returns. It's a survival tactic to get through the inhospitable cold season. Perhaps the most remarkable dormancy ability of palms lies in their seeds. In her book, "Forestry," author Catherine Raven reports that a 2,000-year-old seed from a palm tree was still able to sprout.
Dormancy and Survival
Palm trees killed by severe cold weather may regenerate from dormant buds on the trunk below the soil's surface. Wait to see if any shoots appear before giving up a palm tree for dead. Although the USDA plant hardiness zones offer a guide to whether a particular palm tree species might survive in your climate, there's no guarantee of survival because cold snaps can occur below your area's usual temperature range and kill palm trees.
Cut back on watering palm trees as temperatures drop in the fall. Reducing water supports their natural need to become dormant. Keep indoor palm trees in a cool area, such as an unheated room. Outdoor palm trees in containers are more vulnerable to temperature fluctuations because there's less soil insulating their roots. If you plant palm trees in containers, use the largest possible container. Sudden freezes can do great harm and even kill a palm tree that would otherwise tolerate your zone. Use at least 3 inches of mulch to give roots greater insulation. Apply a sterile commercial mulch 6 inches away from the trunk to avoid the risk of promoting rot and fungus.
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