Need for Pruning

• To accentuate their bark displays and increase the canopy size for more shade, nursery growers often plant and sell birch trees in clumps of two or more trunks. Some birch trees produce suckers, thin sprouts from trunk bases or surface roots, that warrant removal. Rubbing branches, those growing with a narrow crotch angle -- less than 30 degrees -- and broken limbs also call for a little pruning maintenance.
  
  

When to Prune

• From late winter to late spring, birch trees bleed sap heavily from wounds.Photos.com/Photos.com/Getty Images
  
  While other pruning tasks in the landscape center around late winter or very early spring, birch trees are an exception. Gardeners often avoid pruning from winter to early summer to diminish the amount of sap that heavily bleeds from birch trees on open wounds. While not harmful to the birch, the sap may discolor the bark as it flows downward. Light, twig tip pruning is fine but schedule more severe birch tree pruning for mid to late summer, when sap flow is less. You may also prune again in fall after the first frost occurs.
  
  

Important Tree Health Considerations

• Prune birches in late summer, especially on bronze birch borer susceptible species.Jupiterimages/Photos.com/Getty Images
  
  Across North America, many native and exotic birch tree species grown in gardens succumbed to bouts of bronze birch borer infestations and various fungal canker diseases. Avoid pruning at a time of year when the adult flying bronze birch borer insects are laying eggs or when fungal spores are more prevalent, which is roughly May 1 to August 1. This recommendation from the U.S. Forest Service also gives credence to pruning in late summer or fall.
  
  

Pruning Tips

• Birch trees appreciate a cool, moist soil. Do not remove more than 25 percent of a birch tree's canopy as the increase in sunlight reaching the soil can stress the roots. If you must prune the tree during a time of year when borer insects are traveling around landscapes, treat the pruning wound with a preventative insecticide, but do not use wound sealants or latex paint. Hand pruners readily cut twigs less than 1/2 inch in diameter. Use loppers or a pruning saw on larger branches for better cut quality and ease of workload.