FNR-76
forestry & natural resources
WOODLAND MANAGEMENT 
Corrective Pruning of Black Walnut for Timber Form
—By Walter F. Beineke, Associate Professor of Forestry
Pruning black walnut is an art, and this bulletin is intended to provide guidelines, not solutions, for all possible situations. Since each tree in each plantation and each owner is different, none of the photographs provided will look exactly like your trees. However, we hope the resemblance will be close enough to allow you to begin to get the feel of pruning and to decide what should be done in individual situations.  One theory argues for no pruning at all until the tree has developed a tall central stem. Knot-producing low branches on the main stem must then be pruned to allow the tree to develop high quality wood. It is often amazing how a small, crooked tree sometimes straightens without pruning. It is not so amazing, on the other hand, how often low forks, which limit the merchantable length of the tree to two to six feet, develop (Figure 1). All such forks can be avoided by the easy, properly-timed snip of the pruning shears.
Pruning should begin one, or at the most, two growing seasons after the nursery seedling is out-planted and should continue annually until the desired log length has been reached. Pruning is best done in the dormant season from January through March. Sap may run from the wounds, but this will not harm the tree. Some pruning may also be done in late June or early July to remove multiple stems. This is particularly desirable after late spring frost damage.
The principle that is most important to remember when pruning young black walnut trees is to look for overall tree balance. Any leader at the same height as the central leader will tend to force the central leader away from it. Once the competing leader is totally removed, the central leader has the opportunity to adjust and regain overall tree balance. This is because any tree (even crooked and bent black
walnut) attempts to grow in an upright, vertical position. They will do this without the help of pruning, but they may produce two, three, four or more leaders (forks) to achieve that balance. Preferably, black walnut should gain its equilibrium by producing a single, straight central stem. That is where the art of pruning must be applied.
PURDUE UNIVERSITY • COOPERATIVE EXTENSION SERVICE • WEST LAFAYETTE, INDIANA 47907