Don’t forget to keep watering as the season draws to a close. It’s especially important to water evergreens and any trees, shrubs, or perennials planted within the last two years, says Sharon Yiesla, Plant Clinic assistant at The Morton Arboretum.
When they are transplanted, plants lose much of their root systems. It takes a year or more for them to regrow enough roots to efficiently gather water from the soil, and until that happens, they need more moisture in the soil than more established plants.
In the fall, Yiesla says, they need watering to store water and starches in their root systems to get them started in the spring.
Evergreens need water because they keep their water-filled leaves all winter and they don't go fully dormant in the cold months. On sunny, relatively warm days they still will perform photosynthesis, the food-making process, and they need water to do it. Otherwise their leaves will dry out and die.
This is a special danger for evergreens with broad leaves rather than needles, such as boxwoods, although needled evergreens need water too.
Water trees and shrubs with a slow dribble from the end of the hose for a long time, Yiesla says.
Place the hose right at the base of the plant, or farther out under the branches with older, larger trees and shrubs. Make sure to place the dribbling hose beneath the foliage of an evergreen so the water reaches the roots. Don’t use a sprinkler or depend on rain, she says, because the foliage of evergreens can shed water like an umbrella away from the root zone.
Water these needy plants deeply once a week until the ground freezes, Yiesla says, to help them get through the winter and thrive in spring.