Arborvitae (Thuja genus) are evergreen trees and shrubs valued for their dense foliage and ability to form privacy screens. They require consistent moisture to thrive but are highly susceptible to root problems if the soil remains waterlogged. Proper watering requires a precise balance, as both drought stress and excessive saturation can lead to similar signs of decline. The amount of water an arborvitae needs changes depending on the tree’s age, the current climate, and the season.
Watering Requirements by Life Stage
The water needs of an arborvitae change as it transitions from a newly planted specimen to an established tree. For newly planted arborvitae (the first two years), the focus is on encouraging a robust root system. This requires providing consistent, deep moisture to the original root ball and surrounding soil to prevent transplant shock.
During the first few weeks after planting, the root ball should be kept continuously moist, often requiring daily watering for the first 10 to 14 days. After this initial period, frequency scales back to a deep watering two to three times per week, depending on weather and soil type. The goal is to keep the soil consistently damp but never soggy, ensuring water penetrates the full depth of the shallow root system.
Once the arborvitae reaches its second growing season, one deep soaking per week is usually sufficient. This watering should deliver enough moisture to reach a depth of 10 to 12 inches. This practice encourages roots to grow downward, making the plant more resilient to dry spells, and supports above-ground growth as the root system expands.
Established arborvitae (third year and beyond) are significantly more drought-tolerant but still benefit from supplemental irrigation. Although they possess an extensive root network, they are not completely self-sufficient, especially during periods without natural rainfall. These mature trees should be monitored and watered deeply when the top few inches of soil become dry.
In many climates, established arborvitae may only require a deep soak once every two to three weeks during the growing season. In dry regions or during prolonged heat waves, this frequency may need to increase to a weekly deep watering. Providing a deep soak helps replenish moisture reserves in the entire root zone. A single, slow, and deep application of water is preferable to frequent, shallow sprinklings, which encourage weak, surface-level roots.
Adjusting Watering Based on Season and Climate
Environmental conditions modulate the watering schedule for arborvitae, regardless of their age. During the peak of summer, high temperatures increase the rate of evapotranspiration, meaning plants lose water faster. During these hot spells, the watering frequency should be increased to counteract the rapid moisture loss from the soil.
If temperatures rise above 90°F, or if the region receives less than one inch of rainfall per week, the irrigation schedule must be intensified. A mature arborvitae watered every two weeks might need a deep watering every seven to ten days under these conditions. In extreme heat, newly planted trees might require deep watering every other day to prevent the root ball from drying out.
Preparing arborvitae for winter is an important watering requirement, particularly where the ground freezes. Evergreen trees continue to lose water through their foliage in the winter, a process known as desiccation. Since this water loss cannot be replaced when the soil is frozen, it leads to winter burn, characterized by browning needles.
To mitigate this risk, provide a thorough, deep watering in late autumn before the first hard frost and the ground freezes. This practice saturates the soil, allowing roots to store maximum moisture reserves for the dormant period. Conversely, during spring and naturally wet periods, supplemental watering should be reduced or suspended entirely. Overwatering during cooler seasons increases the risk of oxygen deprivation and root rot.
Practical Application and Monitoring Soil Moisture
The method used to deliver water is as important as the frequency and volume. Deep, slow watering is the recommended technique because it allows water to percolate down through the soil profile, reaching the deeper root zone. Systems like soaker hoses or drip irrigation are effective, as they deliver water directly to the base of the plant over an extended period.
When watering, apply moisture directly to the soil over the root zone, which extends past the canopy drip line in mature specimens. Avoid sprinkling water over the foliage, as this encourages fungal diseases and leads to excessive water loss through evaporation. A slow trickle from a hose or drip system should run long enough to ensure water penetrates at least four to six inches into the soil.
Monitoring the actual moisture level in the soil is the most reliable way to determine when to water and prevent over- or underwatering. The simple “finger test” is a practical technique: push a finger four to six inches into the soil near the base of the tree. If the soil at that depth feels dry or crumbly, it is time to water; if it feels cool and moist, watering can be postponed.
A soil moisture meter can provide a more precise measurement of the soil’s hydration level. The tree’s appearance can also provide clues, though symptoms of distress can be misleading. Overwatered arborvitae often display yellowing needles near the base because the roots lack oxygen. Underwatering results in browning or crisping of the foliage, particularly at the tips, but checking the soil is necessary to determine the correct action.