Plants usually do not need much water in the winter since most perennials are in their dormant stage and evergreens slowly absorb water during this time. However, watering your plants before a freeze is beneficial. It not only gives the plants possibly one last water, it can actually help keep the soil warm.
Check the weather forecast. Two to three days before a freeze is expected, plan to water your plants.
Water each plant so that you cover its entire root system, which is usually as wide as the plant's foliage. Generally, about an inch of water is sufficient. Do not get the foliage wet. Water in the late morning, just as the soil warms up, and at the same time, gives the water a chance to seep in before the temperatures drop in the evening.
Mulch over your plants. This will help your plants retain water and it will keep the soil warmer. Use about 3 inches of mulch, which can be any variety such as bark or pine needles.
Water once a month throughout the winter between freezes. Plants usually don't need any more than this during the cold winter months. However, if you live where the ground is frozen all season, then you will have to wait until spring to water your plants. If you live where it freezes on and off, then water your plants once a month when there is no snow or ice on the ground, but a least two to three days before another freeze.