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Generally speaking, the homeowner who is concerned about the effects of winter weather on their palms has little to worry about. However, the unpredictable climate of the winter months can sometimes produce unexpected 'cold snaps'. It is in the face of freezing temperatures such as these that your palms will require extra attention.
Cold weather can affect plants in a variety of ways. First, frost or freezing temperatures can damage the actual tissue of the plant as well as limiting the conduction of water through the trunk. As well, cold weather will slow down the growth of your palm and reduce the activity of the roots. As this occurs, the palm is weakened and susceptible to the perils of disease.
There are, thankfully, a number of preventative measures one can take to encourage the survival of palms through the winter. If you have the advantage of being able to choose where to plant a new palm, ensure that you decide upon a warm and sunny spot well protected from winter winds. Winds from the north and west are particularly harmful. Any number of evergreens will serve as adequate windscreens - fences or walls that allow some air through work well also. If you are able, situate your palm close to the south or east sides of your house. The heat of your home will further protect them.
If you are aware of an oncoming 'cold snap', there exist a number of easy, preventative measures. If your palm is small, a box or blanket placed over it, and weighted down, will protect most species. Be careful not to leave the cover on the plant for more than five days at the most. Burying your smaller palms under a mound of straw or other type of mulch can also provide effective protection for your smaller palms. It should be noted that when the weather warms up, the mulch should be removed immediately so as not to promote rot.
For larger palms with tall, exposed trunks there are slightly different methods of protection. Again, when a colder period is impending, one can protect the plant by tightly wrapping the trunk in burlap, blankets, or similar materials. These materials should also be removed once the weather warms up.
In the case of preventing disease from over-powering a cold-damaged plant there are also proactive measures a homeowner may wish to employ. When a palm is weakened by winter damage, the bacterium that exists on a palm is capable of causing great damage to the plant. Treating your palm with a fungicidal copper spray before the onset of freezing temperatures may help to lower the levels of possibly harmful bacteria. As well, proper fertilization of your palm in late summer and early fall, can help ensure that your plant remains stronger through the winter months.
However, cold-weather damage can and will happen despite one's best laid plans. What, if any, recourse does a homeowner have when faced with a damaged plant? First, it is important to determine the level of injury to the bud tissue inside the trunk. Providing that the tissue has not been too heavily affected, the plant should produce new leaves during the following summer. A fairly accurate test to assess the extent of the damage is too gently tug on a leaf newly emerging from the trunk. If the spear pulls out, there is damage to the tissue of the palm.
If there has been damage to the buds and many of the palms leaves have been killed, the battle is not necessarily over. In such instances, one should remove all of the damaged leaves and shoots from the surface of the trunk, and then apply a copper-based fungicide. Some recommend removing all tissue from the surface of the trunk - with a small saw for example- and consistently spraying the palm with a fungicide until the plant is strong again. In any case, patience is key. Injured palms require an entire spring and summer season to begin their recovery.