As fall looms and temperatures drop, your work in the garden will start to taper off. It's easy to forget about your plants' watering needs when the sun isn't baking them every day, but watering your plants when it's cold is one of the best ways to protect them from frost and icy wind. When plants get damaged or die in the winter, it's usually not the cold itself that kills them, but damage to their cells that occurs when they dry out.
Water the ground well at least 24 hours before a freeze is predicted--if the ground is dry. This will give the roots a chance to soak up the water, which protects the plants from wind damage and keeps the roots a little warmer.
Water the ground, but not the foliage, before a freeze. Frozen water on leaves can cause frost damage.
Water evergreen trees and shrubs during the winter only if there has been a long dry spell. Sudden cold in late fall and early winter can damage plants, but they acclimate as the weather gets gradually colder. Water them before a frost to provide extra protection.
Mulch any trees and shrubs planted within the last year, and avoid planting new plants in the fall. Mulch will help protect young plants' shallow roots from freezing, but newly-planted trees and shrubs are less likely to survive strong winds and frozen soil. Mulch any perennials and biennials you've cut back. Mulch helps the soil retain water, nourishes the plants and keeps them warm over the winter.
Avoid cutting off damaged branches from trees and shrubs until spring. Cutting off branches makes plants more susceptible to water loss and frost damage.