Once established, mulberry trees (Morus spp.) need little special pruning beyond general maintenance. Young trees may need training -- removal of certain branches to allow for proper branch spacing and growth. Because they are deciduous, mulberry trees, which grow in U.S. Department of Agriculture plant hardiness zones 4 through 8, are pruned during the dormant winter months. During dormancy, the branches are free of leaves and buds have not yet begun to form.
Before using tools, disinfect the blades by soaking them in household disinfectant for at least five minutes. Rinse the disinfectant from the tool with water and let it dry. The pruning tools you use will depend on the size of the branch that needs cutting. Use hand-pruning shears on branches under 1 inch in diameter, loppers on branches from 1 to 2 inches in diameter and a pruning saw for branches up to 4 inches in diameter. You should not have much reason to use a pruning saw; cuts over 2 inches in diameter bleed heavily and should be avoided on mulberry trees.
Training Young Trees
When training your mulberry, only remove as much wood as necessary and do not remove more than one-third of new growth in a year on young or established trees. When choosing between a set of close or crossing branches, remove the smaller branch. To create space under the tree, remove branches growing on the bottom one-third of the trunk. Remove branches that cross other branches or grow vertically. Ensure branches are not too close together on the trunk by creating about 2 inches of space between branches. Make cuts just outside the branch collar, the point where the branch joins with the trunk, rather than flush with the trunk.
Lengthy branches may become problematic on newly mature trees as leaves and fruit emerge on the branch end, causing the branch to droop. Cut long branches back to the desired length, making the cut just outside a lateral branch to encourage new growth to form. In July, you can also encourage the growth of new, smaller branches along the main branch by cutting lateral branches back to six leave sets.
Removing Dead Weight
Dead or diseased branches may be removed at any time throughout the year to preserve the health of the mulberry tree. While mulberries aren't prone to pest or disease infestation, the dead wood can still attract insects or fungus. Remove dead branches back to the trunk, making the cut just outside the branch collar. Cut damaged or diseased wood from the tree, making the cut at least 6 inches into healthy wood just outside a lateral branch. Disinfect the cutting tool between each cut to avoid spreading the disease to uninfected wood.