That tree outside your window might look leafless and dormant, but chances are its roots are still active, gathering nutrients and keeping tissues hydrated and healthy. But just like with humans, cold winters can be a challenge for trees.

“A combination of winter’s dry air, little soil moisture and fluctuating temperatures can be hard on trees and shrubs,” says Ryan Statham, district manager with Davey Tree. “With strong winter winds pushing dry air over them, insufficient moisture levels cause them to lack the structure they need to support themselves.”

That means that often, trees do need a little water in the winter. “Their water requirements are generally reduced compared to the growing season,” says Kathy Glassey, arborist and senior consultant at Inspire Green.

With October through March being drier months in much of the U.S., winter watering can become all the more important. However, watering requirements vary depending on the local climate, tree species and soil types.

Here’s what to know about when to water trees during winter.

Why Do Trees Need Water in Winter?

Sometimes, yes. Roots continue to grow, even when soil temperatures drop below 40 degrees. So giving them enough water is vital to help them overwinter and prevent root damage.

Water can also help:

• Springtime growth: Tree roots still absorb water and nutrients from the soil when it’s cold out, albeit more slowly, says Glassey. “The water they store in their roots during winter becomes vital for leafing out with new growth once everything warms up,” she says.
• Prevent dehydration: Lack of water can desiccate tree tissues. This is especially important for evergreens, Glassey says, because they continue to lose water through transpiration. That’s the passage of watery vapor from a living body through a membrane or pores.
• Protect from ice and freezing: Hydrated soil insulates roots from extreme cold. Plus, water-saturated plant cells are less likely to freeze.

When To Water Trees in Winter

If it’s a mild winter and the ground isn’t frozen, continue to water your trees like normal, says Statham. “Evergreens, especially, can get thirsty in the winter, which is why you’ll sometimes see them with brown needles,” he says. “So give your evergreens some extra attention.”

Woody plants with shallow root systems — maples, fruit trees, lindens, honey locusts, hawthorns, oaks and mountain ash — also benefit from winter watering during dry periods. For evergreens, that list includes pine, spruce, fir, arborvitae, juniper, Oregon grape-holly, boxwood and Manhattan euonymus.

“Typically, native trees and shrubs that have adapted to the local climate are often better equipped to handle winter conditions without requiring supplemental watering,” says Statham.