I have had my Meyer lemon tree since it was 2 years. I had no problem with it. This winter I had some work done on the door of the porch where the tree is. It was extremely cold outside and snowing (around 10° F). The door was open and cold and snow entered the porch area. After that day all the leaves and flowers withered and dried off. The tree has not a single leaf on it now. Is it dead? Will leaves grow back?