University of Illinois Extension
Watering trees, shrubs in the fall and winter is a balancing act
 

[November 19, 2021]    After this year’s summer drought in Illinois, it is more important than ever to monitor soil moisture conditions and water trees and shrubs going into winter. Drought conditions in the late fall, along with dry air and low soil moisture, can lead to plant damage if no supplemental water is provided.

“If soil is dry, homeowners should consider watering their trees and shrubs this fall and winter,” says Gemini Bhalsod, University of Illinois Extension horticulture educator.

Plants under water stress are more susceptible to insects and diseases. They can also experience injuries to roots or foliage.

Before watering, check the soil moisture. Monitor the moisture levels about once a week. Dig a small hole under the tree's drip line, 4 to 6 inches is enough. Feel for moisture. If the soil is dry, the tree should be watered.

"This little bit of consistent effort will pay off in the long run,” Bhalsod says.

In particular, newly fall-planted trees, shrubs, and perennials should be monitored and watered late into the season, since they do not have as much time to develop extensive root systems as anything planted in the spring.

Pay attention to evergreens and shallow-rooted trees such as birches and maples. Some shallow-rooted trees can be identified by roots breaking the surface of the soil. Evergreens do not go dormant in the winter and are still actively respiring and lose water through their needles. Dormant trees respire at lower rates. Since soil insulates and cools down later in the year than the air temperature, roots stay warmer longer and respire at higher rates than the above-ground parts, the trunk, and branches, of deciduous trees after their leaves drop.

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Only water when the temperature is above 40°F. In some places, that could be as late as the end of December. Stop supplemental watering after the ground freezes because at this point the trees cannot absorb water through the frozen soil.

To water, use a soaker hose to provide a slow stream of water. Soil should be moist, but not waterlogged. This method results in less runoff and the water is more likely to be absorbed by the root zone. “If your hose is stored away and your tree or shrub is small, pour water very slowly or drill a 1/8-inch hole at the bottom of a 5-gallon bucket and fill that with water,” Bhalsod says.

Water at the tree’s drip line and not right against the base. To conserve water, start with newly planted trees and shrubs weekly and then large and established trees once a month if it is a dry period.

Avoid fertilizer, which stimulates late-season growth, and instead, consider applying mulch. Mulch can help conserve moisture over the winter months. Apply mulch about 2 to 4 inches away from the base of the tree all the way to the drip line in a doughnut shape around the trunk, leaving 2-to 4 inches of space in between. As always, planting hardy species or cultivars with deep roots is best since they are more likely to be able to survive temperature fluctuations and prolonged periods of cold.

[SOURCE: Gemini Bhalsod, Horticulture Educator, University of Illinois Extension]