It's important to water during the winter season.

 

This week would be a great time to water your trees, shrubs and lawn. Anytime the day time temperatures are above 40º F and there is no snow cover, is a good time to do some supplemental watering. We’ve had typical January weather with some snow, but little moisture, dry air and fluctuating temperatures, conditions which can damage trees and shrubs without supplemental watering.  Couple that with the large temperature swing in late November where the temperature was 63º one day and two days later was -13º,  left  the root systems of tree and shrubs very dry.  Often this damage won’t show up until July or August when it is really hot. Your lawn can also suffer from the lack of water, especially if it faces south. Now is the time to do some hand watering. Plan to water around mid-day so there will be time for the water to soak in. You’ll want to water the soil along the drip line of the tree.

As Corinna points out, the drip line is the area under the outer edge of the branches.

You can use a sprinkler, a root feeder (needle) or a soft spray nozzle.

A soil needle or root feeder attaches to your hose.

Insert the needle to about 8", if possible. Leave the needle in the ground about a minute. Continue around the drip line every 18" or so.  If you don’t have a root feeder and for larger areas, a sprinkler is more efficient. Set the sprinkler under the drip line of the tree and let it run for 5 to 10 minutes.  

Or hand water with the nozzle set on a spray pattern. Be sure and disconnect the hose after you’re done watering. Moist soil retains heat better than dry soil. Drought-stressed trees and shrubs are more prone to root damage. Winter watering will help prevent this damage now and get your trees, shrubs and lawn off to a good start in spring