This article was written by David Merriman an ISA arborist and owner of ArborScape Tree Service and Ask an Arborist
 Most homeowners realize the need for watering trees during the growing season. However, you may not realize the need to water in the winter months, defined as October thru March in the arboricultural community.  In fact, it may be more vital to water trees during the winter.
Water Management
Winter tree care begins and ends with adding water and helping trees retain water.  You should winter water your deciduous and evergreen trees up to two times a month between October and March. The reason is, during the fall and winter months, root development still occurs. Tree root systems can spread 2-3 times wider than the height of the tree. Most of the tree’s absorbing roots are in the top 12 inches of the soil. Winter watering keeps this layer moist.
It’s also important to help trees, particularly evergreens, retain water. Because evergreens are still growing throughout the winter, an anti-transpiration treatment will slow water movement through the needles, helping it retain water. 
Maintaining consistent moisture in the winter months prevents drought stress. Drought stressed trees are more vulnerable to disease and insect infestations.  Keep a watchful eye for anything that looks out of the ordinary. Symptoms from lack of water can appear immediately and include browning and drying of needles.
Even though deciduous trees are dormant during the winter, their root systems need moisture to remain alive. Damage from lack of winter watering won’t show up until the following spring and could include branch dieback, or tree mortality.
How to Winter Water
Here is how winter watering works. Water should be applied within the dripline of a tree. The dripline is where the tree branches end all around the tree.
Water deeply and slowly, applying water in a triangular pattern within the dripline. You can use a soaker hose, by hand, or use a deep root feeder. If using a deep root feeder, insert the feeder needle into the soil from 2-8 inches deep and water slowly.
As a general rule, apply ten gallons of water for each diameter inch of the tree. For example, a two-inch diameter tree will need twenty gallons per watering.  
Think of it like a Christmas tree in your house. Without water, it soon dries up and dies. The same thing can happen to the trees in your yard. Water your trees in winter and give it a headstart for the summer.
This article was written by David Merriman an ISA arborist and owner of ArborScape Tree Service and Ask an Arborist