River birch trees, known botanically as Betula nigra, are speedy growing deciduous trees grown as single trunks or in multi-trunk clumps. The trees are prized in the landscape for their leaves on long stems that moves easily and elegantly in the wind and for the decorative peeling park. Training the species into a single trunk form requires significant pruning when the tree is young. Plan to prune your river birch tree in the late spring, summer or fall as this will reduce the amount of bleeding or sap exuded from the tree through the pruning wounds, according to North Carolina State University.
Train young river birch saplings into single trunk trees by selecting a strong, fat and straight central leader or vertical branch that is close to perpendicular to the soil line. Prune away all other vertical trunks and branches growing around the chosen central leader as needed. Place the cut down to the ground or just below the soil surface. Be ruthless as any other shoots draw nutrients and plant resources away from developing your central trunk.
Inspect the tree regularly and remove any damaged, dead, diseased, cracked, abrading or otherwise compromised branches, twigs or foliage. Cut back to the point of healthy wood or all the way back to the parent branch just outside the swollen branch collar.
Prune the canopy of river birch lightly and infrequently and only as needed to control the height or spread when interfering with nearby trees or structures. Cut just the branch tips or small branches following the natural form of the canopy.
Pull all cuttings from the canopy and up from the soil surface to prevent the cuttings from breeding disease and insect activity. Burn or otherwise discard any cuttings suspected of harboring disease or insects. Healthy wood can be chipped and composted or use decoratively.