Answer: Arborvitae (Thuja) does best in soil that is evenly moist although when well established it becomes more drought tolerant. We had some very dry weather, so that may have caused some difficulty to the plants while they are trying to root into the native soil. It is also possible that the potting soil they grew in originally dries out faster than the surrounding soil. If it has been raining and the soil is moist (dig down and see) then you may not need to water. When you water, provide a slow deep soaking rather than a daily light sprinkling, but also keep an eye on the original rootball to make sure it is also staying moist. These plants are not too fussy about soil as long as it is at least average in fertility. During the first few years, watering as needed will be the most important thing you can do. Make sure the soil is moist even going into fall and winter until it freezes. You should also use several inches of organic mulch (do not allow it to touch the stem/trunk) to help keep the soil moist and hold down weed competition.
If you should lose just two out of 25, that would still be within typical tolerances for transplanting for commercial landscaping work. Good luck with your arborvitaes!
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