This story was originally published in March 2018.
Maine may still be in the clutches of winter, but — if you can believe it — the best time to prune apple and pear trees is now, before spring officially arrives.
“This is the time of year when the temperature starts to warm up and there’s less danger of interfering with the natural hardiness when you prune,” said Renae Moran, University of Maine Cooperative Extension fruit tree specialist and associate professor of pomology (the science of growing fruit) for UMaine’s School of Food and Agriculture.
Moran works at Highmoor Farm, a UMaine fruit and vegetable research facility comprised of 278 acres on Route 202 in Monmouth. Home to 17 acres in orchards and five acres of vegetables and small fruits, the farm also includes two large barns, two laboratories, a shop, 10 cold storage lockers, two hoop houses and a greenhouse.
“We start pruning our trees in January, and we don’t get finished until the end of March or April,” Moran said of the Highmoor Farm orchards. “It takes us all winter.”
For college courses and public workshops, Highmoor Farm has a teaching orchard filled with a wide variety of fruit trees to demonstrate how certain trees are cared for differently than others.
“For apples and pears, you want to be done pruning by the time the trees start to break [bud or grow], which is the end of April,” Moran said, “and that’s because as it warms up, there’s a disease that starts to build up and that’s called fire blight.”
Fire blight is a contagious disease that affects apples, pears and some other members of the family Rosaceae. Caused by a bacteria, it can be spread from tree to tree on pruning shears. Therefore, you want to prune your trees before the bacteria becomes active.
“Fortunately, here in Maine, it’s not a huge problem,” Moran said.
The opposite is the case for stone-fruit trees, such as peach and cherry trees, Moran said. It’s best to prune stone-fruit trees after they start to grow. Again, the reason is disease. Stone-fruit trees are susceptible to bacterial canker, a disease that tends to attack branches through pruning cuts and leaf scars. During the growing season, pruning cuts heal more quickly, which means the trees are less likely to become infected.
“These are just guidelines,” Moran stressed. “It’s still better to prune the trees than not. Pruning is one of the best things you can do for fruit trees.”
Pruning prevents fruit trees from growing in a way that’s counterproductive to producing fruit. For example, fruit trees naturally grow many shoots and large branches, which shades the interior of the tree and lower branches, making fruit production there poor or impossible. The goal while pruning is to create an open canopy that allows light through, encouraging the production of larger fruit.
This and more is explained on the Maine Cooperative Extension website in the section “Growing Fruit Trees in Maine,” which Moran co-authored with Glen Koehler, UMaine associate scientist specializing in integrated pest management. The website provides a wealth of information about fruit trees, from planting and early care to pollination requirements to diseases and pests that plague fruit trees.
In addition, a number of fruit tree pruning workshops are held throughout the state by the University of Maine and the Maine Organic Farmers and Gardeners Association.
In addition, the UMaine Cooperative Extension Master Gardener Volunteers program includes plenty of information and hands-on practice with fruit tree pruning. For more information, visit extension.umaine.edu/gardening/master-gardeners.
