You should always prune with sharp, clean tools to prevent injury, ragged cuts, and disease. Take care to clean your trimmers, saws, and pruning shears between uses, thoroughly drying them and storing them in a clean, dry place. If pruning is done properly, there is nothing to put on pruning cuts then. If you want to, first remove all jagged edges where the tree limb was cut also remove dust debris from the limb stub. Dip a paintbrush in the container of liquid pruning sealer, and use the paintbrush to coat the limb stub with the sealer. Allow the sealer to dry for one hour, and then check the stub to ensure it is completely covered with the sealer. The research from the University of Arizona says that you should not use pruning sealers after pruning your trees or shrubs. In fact, it found that pruning sealers actually obstruct trees' natural healing power. Plus, pruning sealers may trap moisture in the tree, which can encourage wood decay or fungi.