Arborvitae (genus Thuja) are popular evergreen conifers valued for creating dense, year-round privacy screens and hedges. Despite their hardy appearance, these plants are not drought-tolerant and require consistent moisture, especially during their establishment period. The most effective way to ensure the long-term health and vibrant color of arborvitae is by consistently providing deep, thorough watering. Shallow, frequent watering encourages shallow root systems, making the plants vulnerable to heat stress and drought. A deep soaking technique encourages roots to grow downward, leading to a more resilient and stable plant.
Determining When to Water
The frequency of watering should be dictated by the dryness of the soil, not a rigid schedule. A simple diagnostic check is necessary before applying water. The most reliable method is the finger test, which involves pushing your index finger two to three inches deep into the soil directly beneath the plant’s canopy. If the soil at this depth feels dry, it is time to water; if it feels cool and moist, you can wait a few more days. This test is crucial because surface soil often dries out quickly, giving a false indication of the moisture level at the root zone.
Visual cues from the plant can also signal a need for water, though these signs usually appear after the plant has already experienced some stress. Drought stress often presents as yellowing or browning foliage, sometimes referred to as “flagging,” which typically starts at the tips or the exterior of the plant. If the browning is occurring deep inside the canopy near the trunk, it is usually a normal seasonal shedding process and not a sign of thirst. Recognizing these initial signs allows for a timely intervention before the stress becomes severe.
The Essential Slow Soak Technique
Applying water slowly and deeply is the most effective method for arborvitae, ensuring the water fully penetrates the dense root ball and surrounding soil. The goal is to saturate the soil to a depth of at least 8 to 12 inches to encourage deep root growth. Using a standard garden hose requires setting the flow to a very slow trickle, or a steady drip, which is the mechanism of the “slow soak” technique.
To execute this, place the end of the hose on the ground at the base of the arborvitae, positioned slightly outside the trunk to avoid direct contact and potential rot. The flow should be low enough that the water slowly soaks into the soil without running off or creating puddles on the surface. This controlled, minimal flow rate prevents water waste and ensures deep saturation of the root zone.
The duration of the soak varies significantly based on plant size, soil type, and hose flow rate. A general starting point is to let the hose run for 30 to 60 minutes per plant. For a very large specimen, this duration may need to be extended to an hour or longer to achieve the necessary saturation. After an initial watering session, you can verify the depth of penetration by digging a small hole or using a soil probe a few feet from the trunk; the soil should be consistently moist down to the target depth.
While an open hose on a trickle works well, using a hose splitter to connect a soaker hose or a drip line laid in a spiral around the base of the plant can make the process more efficient. These tools deliver water directly to the root zone with less supervision, but the principle of a slow, prolonged application remains the same. This technique is designed to mimic a long, gentle rain, which is far more beneficial than a quick blast of high-pressure water.
Adjusting Watering Based on Season and Age
The frequency of the deep soak must be adapted to the plant’s age and the current environmental conditions. Newly planted arborvitae, defined as those in their first two growing seasons, require much more frequent attention than established plants. During the first year, they have a small, confined root system and need the soil to remain consistently moist, often requiring a deep soak every one to three days, particularly during warm weather.
Once an arborvitae is established, typically after two years, its root system is extensive enough to tolerate longer intervals between watering. Established plants only require a deep soak during periods of drought or extreme heat, usually once a week or every two weeks, depending on the climate. The requirement for deep watering increases when temperatures exceed 80 degrees Fahrenheit and natural rainfall is absent.
Seasonal changes also necessitate adjustments, especially in the late fall. Before the ground freezes completely, providing a final, extensive deep watering, known as winter watering, is important. This practice ensures the foliage and roots are fully hydrated, which helps prevent winter desiccation. Winter desiccation occurs when the plant loses moisture from its needles faster than the frozen roots can replenish it. The plant is largely dormant in the winter, requiring minimal to no watering unless the weather is unseasonably warm and the ground is not frozen solid.