Answer: Daily watering might be a little excessive. Arborvitaes should get along with one deep soaking per week. It's important that the water be applied slowly so that it has a chance to trickle down and wet the entire root mass. You can set a sprinkler on low to accomplish this, or build a watering basin beneath each; fill the basin, allow it to drain, then fill it a second time. If the weather is really hot you might want to water twice a week. Deep soaking will encourage deep root growth so your arborvitaes can survive droughty conditions; daily waterings will keep the roots close to the surface where they become dependent on daily waterings.
The dry spots might be a result of winter damage or could indicate an insect infestation. Spider mites are common on arborvitaes. They prefer the dusty, dry interiors of the plants. Look for webbing in the foliage and along the stems. You can also take a sheet of white paper, hold it near the center of the plant, and shake or thump the branches. If you find little specks that look like pepper on the paper, and if they move, you've probably got spider mites. There are miticides in the gardening section of home improvement stores or at your favorite nursery. Apply according to label directions.
Best wishes with your arborvitaes!
Q&A Library Searching Tips