Southern crab apple (Malus angustifolia), or narrow-leaf crab apple, is a native tree found in the southern United States that grows to 30 feet tall and produces pink to white flowers in the spring followed by tart, elongated fruit. Pruning Southern crab apple is complicated by thorns located along its branches. It requires acid soil and some sunlight to thrive. Although considered a weed tree, it can be found in many natural areas. It should never be planted near red cedars as it is susceptible to red cedar rust.
Remove suckers from Southern crabs whenever they appear---usually in spring. Cut the new growth with a sharp pruning saw or shears as close to the ground as possible. The tree should be kept to one leader or main trunk because, left to its own growth habit, it can create a thicket of thorny shrubs.
Prune crab apple trees during their dormant season in late winter before spring buds begin to form. Crab apple blooms in late spring; fruit follows blooms on new growth, maturing in the fall. Dead branches should be removed any time of year.
Prune any low branches from the leader to form a healthy trunk. Cut close but not into the lumpy bark branch collar near the trunk. This collar will close over the vulnerable edges around the branch if left undamaged. Double-cut branches more than 2 inches in diameter to avoid fracturing the hard wood. Make a cut up from the underside a few inches out from the trunk and a second cut down near the collar all the way through the branch.
Preserve the main leader of Southern crab apple. This wild tree tends to be self-pruning in natural settings but it might need occasional shaping to make it a good neighbor in civilized gardens. Remove branches when they are small and never more than a third of a lateral branch at a time.
Maintain your Southern crab apple's top portion or crown by never clearing more than a third of the lateral branches along the trunk, always leaving two-thirds of the crown intact. Prune branches back that rub against each other or cross in the crown. But if more than one-half of the leaves has to be removed, take the entire branch, taking care not to damage the branch collar.