Gardening with Allen: Topping, improper pruning weakens large trees

If you are concerned about wind damage to trees, the best way to prune them is to open them up by removing some of the inner branches so that wind can blow through the trees more readily. This practice is called wind sailing because it allows the wind to sail through with less resistance. Wind sailing is not recommended for large spruce and cypress trees, but it is for firs, pines and most deciduous trees.

Large branches can be shortened back to side branches that are at least one-third the size of the branch being shortened. This is sometimes called drop-crotch pruning. The crotch is the point where two branches connect. A trained arborist can use these techniques to reduce a tree’s size by as much as 25 percent.

If major branches are simply stubbed off at an arbitrary length without regard to side branches, severe damage can occur. If a weak or damaged branch does not have appropriate side branches, it is better to remove it completely back to its origin.

Needle evergreen trees should never have the center trunk topped or shortened. Stubbing or topping large branches of broad leaf trees causes them to produce many weak water-sprout branches that grow straight up. These water sprouts grow very rapidly, quickly reaching the tree’s previous height in a year or two. Because of their weak connections to the larger branches, they often break.

The wounds created by stubbing large branches are also susceptible to insect and disease infection. Some branches will die back, creating an even larger target for infection. The multitude of small branches growing like a witch’s broom on the end of bare larger branches destroys the natural shape and beauty of the tree.

Large poplars or cottonwood trees (including the new hybrid poplars) should not be planted close to structures. Their wood is more susceptible to wind damage than slower-growing trees. Poplar trees should only be pruned or removed by a licensed professional arborist.