Are you planning to get some pruning done on an early October weekend? Put down those pruners. It’s too soon.
“Shrubs and trees shouldn’t be pruned in fall until they are fully dormant,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “That may not be for several weeks, in November or even December.”
Pruning before plants enter dormancy may stimulate them to sprout new growth. Those tender new green shoots, which will not have time to develop sturdy protective bark, may be damaged when the first really cold weather hits.
Avoiding that kind of harm is the reason our deciduous trees and shrubs — those that lose their leaves in fall — enter the sleep-like state of dormancy each autumn to wait out the harsh weather of winter. “Pruning at the wrong time defeats their self-protection,” Yiesla said.
How can you tell whether a plant is dormant? A tree or shrub that has lost all its leaves is usually in dormancy. To be safe, wait until most of the shrubs and trees in your neighborhood lose their leaves. “You’ll know they’ve felt enough cold weather to reach a consensus that it’s time to shut down,” she said.
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There’s no safe date when you can assume trees and shrubs will be dormant. As our climate has changed, autumn has tended to be warmer and last longer. But it’s also more volatile and less predictable, with wider swings in temperature and late warm spells. That may cause plants to delay dormancy. “The calendar is less relevant now than the weather forecast,” Yiesla said.
Watch the weather and pay attention to your plants to judge when you will safely be able to prune. In the meantime, the most useful thing you can do in the garden is water.
Plants need water all through the fall. Even after their leaves drop, their roots are still growing. Roots continue to grow as long as the soil is above about 45 degrees, and the soil takes much longer to cool down than the air does. “Even after you need a warm coat, roots may still be growing,” she said.
Fall rains are undependable and may not provide enough water to support root growth. Continue to check regularly to see if the top 2 inches of the soil feels moist. If it’s dry, water deeply enough so that the water soaks down 4 or 5 inches.
Autumn watering does more than help roots. Evergreen trees and shrubs need to store plenty of water in their leaves and stems as well as their roots to resist drying out in the cold winter winds. Water them as necessary until the ground freezes.
“Making sure your trees and shrubs go into winter with enough moisture will set them up for good growth in spring,” Yiesla said.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or [email protected]). Beth Botts is a staff writer at the Arboretum.