Ornamental trees need to be pruned both for aesthetic reasons and to help with tree health. Precisely how to prune your tree will depend on the variety. Different trees need to be pruned to different shapes. Weeping trees are generally pruned into a dome shaped canopy, while trees like maples and cherries often should be pruned to a single leader with upward reaching branches.
Remove any deadwood, including twigs and branches, at any time of year. Deadwood places additional stresses on the tree and uses resources better suited to growth and flowering. Remove deadwood about the size of a pencil or smaller with a pair of pruning shears. Remove larger deadwood with a pruning saw.
Prune branches starting from the bottom of the tree to the top. Remove branches at the collar, or swelling where the branch to be pruned grows from the larger trunk or branch. Leave a bit of the collar on the branch or trunk.
Prune the tree from the inside of the tree to the outside twigs once the lower branches have been removed to your satisfaction. Use the same technique with pruning shears for branches smaller than about the width of a pencil and a pruning saw for larger branches.
Prune your tree at the recommended time. Different trees should be pruned at different times. For most trees, winter pruning is safe. For other trees, pruning after the growing season is best. Check with a reputable nursery for the best time of year to prune your particular variety.