Winter Tree Pruning
Sue Hartman, Garden Hotline Educator
February 8, 2014
Winter is a perfect time to prune many trees in the Pacific NW. In the Seattle area, dormancy begins in late November or December when plant growth becomes temporarily inactive. This enables a tree to survive freezing temperatures. Dormancy usually lasts until mid-February, depending on Mother Nature. During this time, the bare branches of a deciduous tree make it easy to discern its structure for shaping purposes. Plus, when temperatures warm up in March the tree’s energy focuses on producing new growth. If you remove too much foliage at this pivotal time, the tree will need to direct its energy toward replacing the missing leaves instead of putting on new ones.
The foremost reason to prune any tree is to keep it healthy. The leaves on trees make food that helps keep the tree alive. Trees that grow in urban areas have a tough enough time as it is due to close living quarters and pollution. Do not take more than a quarter of the total foliage in one year. If a tree needs a lot of work, make a plan to do it over a number of years. Not all trees need to be pruned, so understand why you are going to prune before you make a cut. Healthy trees that have been properly pruned when young will need much less pruning as they mature. Never top a tree unless you have a specific reason to do so. Some fruit trees can handle much more pruning, including topping, than ornamental trees and are pruned to manage fruit production. Topping does not work to reduce the size of an ornamental tree. Over-pruning or topping can cause a tree to send out many weak sprouts in order to replace what was lost. Some trees will develop a new, weak leader to replace what was topped, creating a possible safety hazard in a strong windstorm.
Not all trees are candidates for winter pruning. Some will produce an abundance of suckers or water sprouts. Prune these trees in the summertime to prevent suckering: Cornus (dogwood), Magnolia, Malus (crabapple), Viburnum, and Hamamelis (witch-hazel). Wait until June or July to prune ornamental and sweet cherry, plum, peach and almond trees. These trees are all susceptible to many fungal and bacterial diseases. Every cut you make is a potential point of entry for disease producing organisms. Pruning during the dry season helps reduce the risk of infection. Even during the winter it is best to prune on a day when it isn’t raining in the Pacific NW where fungi thrive. And it is easier to see what you are doing when raindrops are not obscuring your vision!
Birch, beech and maple trees may “bleed” or release sap when they are cut. Less sap will flow if you wait until after a hard frost to prune – provided there IS a hard frost! If there isn’t, you can wait until summer to prune these trees. In order to lessen damage from elm leaf borer and Dutch Elm Disease, prune elm trees only when the trees have no leaves (mid-October to mid-April).
Some municipalities require a permit to prune or remove a tree, so check with your local city arborist, agriculture or forestry office for more information. The City of Seattle requires anyone who prunes or removes trees that are planted in a public right-of-way (parking strip or public utility easement) first obtain a street use permit. For more information, call 206-684-TREE (8733) or visit their website: www.seattle.gov/transportation/treepruning.htm.
Once you have figured out when to prune which tree—and once you’ve cleaned and sharpened your pruners—begin by removing the deadwood and branches that cross or rub against other branches. Next, remove any branches growing into the center of tree. Then if there are any tall branches growing at the top of the tree (up to 1 ½ inches in diameter), thin or head some of them back. This will allow more light to reach the lower branches and keep the tree from growing too tall too quickly.
Many fruit trees including apple, European pear, quince, elderberry, mulberry, and medlar can all be pruned in winter before the buds swell. Pruning fruit trees help them produce more fruit and lessen the risk for disease. By letting in more sunlight and air (especially at the top of the canopy) the tree will be better equipped to fight disease and fruit that was hidden by foliage will ripen. Fruit trees will need strong branches to hold up heavy fruit without breaking, so remove branches that are weakly attached.
If you love trees and want to help protect our urban landscape, become a Tree Ambassador! You’ll get to design “street walks,” renovate areas taken over by invasive weeds or even adopt a young street tree and help it live a long and healthy life. Training opportunities begin in March. Learn more at www.seattle.gov/trees, or reach the Tree Ambassador program via email at firstname.lastname@example.org or by phone: (206) 615-1668.
If you have a pruning job that is more than you can handle, contact Plant Amnesty. They have a wonderful arborist referral service and loads of helpful pruning information online at: www.plantamnesty.org/home/index.aspx. To learn more about pruning specific plants, please contact the Garden Hotline at (206) 633-0224 or www.gardenhotline.org. You can also find us on Facebook, Twitter and YouTube.