Answer: Even though the weather is cold and you don't see any new growth, landscape trees and shrubs still need water because their roots are busy growing until the soil freezes. If the soil doesn't freeze in your garden, plan on watering once a week during the winter months. If it does freeze, you can stop watering until the soil thaws. Roots will grow as long as the soil temperatures are above 40F. I'd water the trees during the winter months until they are well established - 3 or 4 years after planting. After that, natural rainfall should provide all the moisture they need during the winter months. The easiest way to water to to make a basin or a watering well beneath each tree or shrub by mounding up soil in a circle about 12" away from the trunk, all around the trunk or main stem. Fill the basin with water, allow to drain, then fill it a second time. This concentrates the water directly over the root mass and allows it to trickle down, wetting the entire root area. Do this once a week.
Your Emerald Green Arborvitaes are probably acting normally. All the new growth is at the ends of the stems and evergreens routinely lose their oldest leaves (those near the center of the plant). You can hose off the old foliage which will make the plants look neater and will also discourage spider mite insects which tend to congregate in dry dusty places such as the centers of arborvitaes.
Enjoy your garden!
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