I have 140 feet of Arborvitaes using them as a screen/fence in my back yard. The lower 60 feet are about 17 years old and the upper 80 feet are about 8 years old. They are about 20 feet tall with the younger ones about 4 feet wide from the trunk to the outer edge and the older ones 5 feet wide. Throughout their life, I have topped them to make them grow full and act as a screen. In 2014, I cut about 4 to 5 feet from the tops of the older ones and about 3 feet from the younger ones. Local landscapers have told me that if you do not continue to top them, the bottom branches will thin and die. Is that true? Should I continue to top them or let them grow? Again, my concern is to screen so the bottom section of the tree is most important. Should I clip/trim the outer ends of the branches at the bottom to stimulate growth and make them fuller? Thank you for your help,
Pittsfield, April 2016
Arborvitae will produce growth from dormant buds on old wood. The lower branches need sunlight and air flow to grow so you will need to continue to trim these trees. Both the vertical shoots at the top and throughout the tree should be trimmed so that they don't shade and prevent air flow for the bottom branches. The trimming stimulates further growth. The base of the shrub should be wider than the top. This will also help prevent tree damage from ice and snow buildup in the winter.