Answer: It's really difficult to diagnose a plant problem long distance, but what you describe is not normal for arborvitaes; they typically retain their foliage all year around, although they do drop some of the oldest foliage (that near the center of the plant) as they mature. Losing all the foliage indicates some stress - either drought or overly wet soil, or an environmental, insect or disease problem. One deep soaking per week is generally all the plants need so you may be over-watering at this point. I think it's natural to want to provide water to plants that appear to be browning, but too much water will drive the oxygen out of the soil and essentially drown the roots. I'd dig one plant up and inspect the root system; healthy roots are creamy white inside - anything soggy or mushy indicates root rot. If you find damaged roots and the damage isn't too extensive you can prune it away and replant. If most of the roots are involved, it may be too late to save your arborvitaes. Wish I had something more positive to offer. Best wishes with your plants!
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