I have four emerald green arborvitaes that are 9-10' tall and about 8 years old. During the high winds of the storm on 2 March I noticed a couple of them starting to lean over so I went out and tied some support rope around them. I'm pretty sure if I hadn't been home they would have blown over, although they are next to a pergola that may have kept them mostly upright depending on which direction a particular gust came from. Are these shrubs normally shallow-rooted, or is it possible I have issues because they are planted next to a stone patio? Should I do anything to make sure I don't have this issue in the future?
In general arborvitaes can be shallow rooted. In this area the trees have a limited area for the root system to grow. Hopefully the trees will straighten up and then you can remove the rope. This is a tough site next to the fence and patio. So far, the trees look good. All you can do is water the trees during dry periods and make sure mulch is no thicker than several inches and keep away from the trunks. Eventually the trees may brown out on the fence side due to lack of sunlight and good air circulation.