From The Ground Up: Time to trim those oak trees now

That small window of opportunity to trim oak trees (December through the end of February) is quickly nearing its end, so if you still have this item on your winter to-do list, better get to it soon. Why only a few months to prune my oaks? Oaks are susceptible to oak wilt, a fungal disease which is spread by sap-feeding beetles. Beetles travel from an oak wilt-infected tree and land on a healthy oak tree, which transfers the disease to an otherwise healthy tree via the beetle. Trimming your oaks during total dormancy in winter enhances your chances that your oak will not contract this deadly disease. If by chance your oak is damaged by a storm and pruning is necessary during spring or summer, latex house paint should be applied to the cut (within 15 minutes) to avoid attracting the beetles. Oak trees are the only exception to the no-paint rule.

What about pruning shade trees? February and March are the best months to prune and allows you to take a good look at the structure of your tree without the presence of foliage. The walling off or compartmentalization of wounds occurs most rapidly just prior to the onset of growth in spring. Profuse amounts of sap may flow during this time, but the tree won't bleed to death, although it may appear that it is. It's okay to trim in midsummer too, but avoid spring, when the trees are leafing out or fall when the leaves are dropping.

The best time to trim fruit trees is late February through early April and avoid trimming during the summer months. Water sprouts can be removed in June or July.

Avoid flush cuts when pruning but rather make your cut just beyond the branch collar and branch bark ridge, which will enhance wound compartmentalization and callus formation. For branches greater than 1 1/2 inches in diameter, use the 3-cut method. The first cut will be 6 to 12 inches from the main branch or trunk. Cut upward and about one-third of the way through the branch. The second cut will be 1 to 2 inches beyond the first cut, sawing downward from the top of the branch. After the second cut is made, the weight of the branch will cause it to break between the two cuts, thus preventing the branch from tearing a large piece of bark as it breaks. The final cut will be just beyond the branch collar and branch bark ridge.

For newly planted trees, severe pruning can actually slow plant growth, so allow only minimum, corrective pruning. It's okay to remove double leaders or dead, broken or crossing branches but that's about it. The lower branches help stabilize the tree and provide food for the growing tree. You can start to prune those lower limbs in 5 to 10 years. Enjoy your maintenance-free tree for the few years that you can!

For questions, call the Linn County Extension Master Gardener Hotline at (319) 447-0647.