What has happened to my holly bushes this winter
My holly bushes have lost most of their foliage this winter. They were well established bushes, about 5 feet high, and have always been healthy. I even cut a few small berry branches for Christmas décor. They were fine in November, then I noticed most of the leaves have fallen and the bush is almost bare. This winter in northern NY has been extremely frigid and I did not really notice when the foliage started to fall. The bushes have been established for many years and I have pruned them once, about two years ago.
Since this was an especially cold winter, there's a good chance that your holly is suffering cold damage. Holly is native to more southern climes, and while many varieties have been developed to withstand northern winters, the weather may have been too much for yours. If it sends out leaves in the spring, all is well. You might want to take or send a sample of twig and leaves to your local extension service to eliminate the possibility of pest or pathogen. This site will help you locate one: https://www.gardeningknowhow.com/extension-search/