Answer: Antidessicant sprays can be used to help stop or slow moisture loss through the foliage of evergreens over the winter. They are especially helpful to newly planted shrubs or trees where the roots may be stressed and therefore less able to absorb adequate moisture.
They are applied in late fall when temperatures are still somewhat mild and usually need to be applied again later in the season. They are commonly sold in garden centers, usually as a concentrate to be mixed with water.
In my experience, if your plants are healthy and have been in that location for 40 years, they may not require any special protection during the winter. You might simply make sure they are well watered through the fall to help assure adequate hydration prior to the cold weather. The soil should be kept moist (but not sopping wet) until it freezes.
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