Answer: Windmill palms are the hardiest of all palms, but they are susceptible to winter damage. You can minimize the impact of winter on your palms by proper siting and by following good cultural practices.
The kind of winter weather that is hazardous to palms is a "cold snap" during which the temperature falls below 15 degrees, usually following a spell of mild or rainy weather. In the typical "cold snap," temperatures can drop by as much as fifty degrees in the space of a day or less. Cold snaps are usually accompanied by strong winds that come from the north or northwest. Palms are generally very susceptible to these winds. A combination of ground freezing, large evergreen leaves, and strong wind can subject palms to severe moisture stress. Under such conditions palms can become literally freeze-dried. The best way to avoid this unpleasant outcome is to plant your palms in a warm, sunny spot protected from winter winds, especially winds from the north and west. It is also helpful to plant palms fairly close to a house, where the roots will be protected against ground freezing by the heat of the house. The best sides of the house to plant on are the south and east sides (although the opposite is true for other broadleaf evergreens such as camellias). Since cold air tends to collect in low spots, it is generally best not to plant most species of palms in these "frost pockets." The same holds true for exposed hilltop locations. If you know that a severe cold snap is on its way, there are a number of easy methods of protecting your palms. A cardboard box or a quilt placed on top of a small palm, and weighted down with a bricks or rocks, can provide adequate shelter for most cold-hardy species. The cover should be removed after four or five days, at the most. Another effective "low-tech" way of protecting fairly small palms is to temporarily bury them under a mound of pine straw or some other type of mulch. Most of the mulch should be removed once the weather warms up. Leaving the mulch on top of the plant can promote rot. Palms with a tall, solitary trunk tend to be the most vulnerable to winter cold damage. If you know that a severe cold snap is on its way, you can help prevent damage to your trunked palms by tightly wrapping the trunk with burlap, old blankets, or some similar insulating material (We don't recommend plastic). Some palm enthusiasts go to extreme measures to give winter protection to species that are marginal for their area, building temporary shelters for these plants and adding outside sources of heat during cold spells. Hope this information provides some guidance!
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