Trees require water year-round, even during the cold season when they enter a period of reduced metabolism known as dormancy. This state is not a complete shutdown of biological functions. Assuming all watering should cease once temperatures drop can lead to serious health problems, especially in regions with dry or windy winters. Maintaining proper hydration supports root health and prepares the tree for spring growth.
Dormancy Does Not Mean Dehydration
Dormancy is a protective phase where a tree conserves energy and growth largely stops above ground. Below the soil surface, however, metabolic processes and root activity continue, requiring a steady supply of moisture. Tree roots remain active and grow slowly throughout the winter, provided the soil is not completely frozen. This continuous below-ground activity consumes water, making it necessary to replenish soil moisture.
The water needs of trees vary based on leaf retention. Deciduous trees shed their leaves and lose significantly less moisture during winter. Evergreen trees, including conifers, retain their needles or leaves and continue to lose water through transpiration. This continuous moisture loss makes evergreens particularly susceptible to drying out during dry or windy winter conditions.
Indicators That Watering Is Needed
The decision to water a tree in winter depends entirely on environmental conditions rather than a fixed calendar schedule. A crucial indicator is a prolonged period of low precipitation, such as two to four weeks without rain or significant snowfall. Snow cover naturally insulates the soil and provides a slow, steady release of water as it melts. Without snow cover, the soil is exposed to drying winds and can freeze deeper.
Consider watering when the air temperature is consistently above 40°F (4°C) for several days, ensuring the top layer of soil is thawed. Watering frozen soil is ineffective, as the roots cannot absorb the moisture. Check the soil moisture by inserting a screwdriver or small rod about two inches deep near the tree’s drip line. If the soil feels dry at this depth, moisture is needed. Established trees benefit from a deep soak once or twice per month during dry winter spells.
Proper Techniques for Winter Watering
When watering is necessary, the application method must be slow and deep to ensure moisture reaches the root zone without causing runoff. A soaker hose or a slow-drip system is the preferred method, allowing water to penetrate the soil to a depth of at least 12 inches. Avoid using a high-pressure hose or sprinkler, which encourages shallow root growth and wastes water through evaporation or runoff.
The best time of day to water is midday, which allows the moisture to absorb into the soil before evening temperatures drop and cause refreezing. For young or newly planted trees, which have limited root systems, focus on moistening the area just outside the base of the trunk. Applying a two to four-inch layer of organic mulch around the tree, kept a few inches away from the trunk, helps regulate soil temperature and conserve moisture.
Risks of Root Desiccation
Insufficient winter watering can lead to root desiccation, the severe drying out of the tree’s root system. When the soil is dry and frozen, the tree cannot replace the moisture lost through its tissues, particularly in evergreens. This inability to draw water from the soil results in a condition commonly known as “winter burn.”
Winter burn appears as browning or discoloration, often on the side of the evergreen facing the prevailing wind and sun. The damage occurs because the needles continue to transpire water into the dry, cold air, but the frozen roots cannot replenish the supply. This damage weakens the tree and can lead to branch dieback or the death of young or vulnerable specimens.