There are over 65 species of ash trees (several common species are the blue ash, European ash, green ash and white ash). Ash trees can range in size from small to extremely tall and large. They are often used as a shade tree. Ash trees will require pruning to remove dead, damaged or diseased branches, to remove branches for safety reasons, or to control size within your landscape design (clearance under the tree or width of the tree).
Cut away damaged or diseased branches or limbs as soon as possible. Make a clean cut. Clean cuts ensure the health of the tree as ragged or torn edges provide an entryway for pests and disease. This can be done at any time of the year--the tree does not have to be in its dormant stage.
Trim for safety reasons and to control the size (width) of the ash tree by cutting off selected branches or limbs. Locate the branch collar (this is on the underside of the branch where it connects to the trunk) and the branch bark ridge (this is on the topside of the branch where it connects to the trunk). Cut right in front of the branch bark ridge and the branch collar. Do not cut into the branch collar or branch bark ridge. This can be done in early spring or late fall when the tree is dormant.
Visually inspect the crown of your tree. Remove deadwood and crossover branches. Tree professionals call this "thinning of the crown." Thinning is generally performed on a mature tree by a professional tree service. Arborists can determine what branches need to be cut without damaging the appearance, health or integrity of the tree. Tree service professionals are also accustomed to working at the required heights, and they have the necessary equipment for the job. This can be done in early spring or late fall.
Cut away any suckers; these are shoots that appear at the base of the tree or any that you see growing from the roots. (These shoots take away valuable nutrients from the tree.) You can do this at any time. Shoots generally appear during the growing season.