The Emerald Green Arborvitae (Thuja occidentalis ‘Smaragd’) is a popular coniferous shrub in landscaping, prized for its dense, naturally columnar growth habit. This evergreen is widely used for creating privacy screens and hedges due to its uniform, deep green foliage. Because of its shallow root system, the plant is particularly sensitive to moisture fluctuations throughout the year. Providing the correct amount of water is the most important factor for the establishment and long-term health of this popular plant. Successful cultivation requires understanding the difference between watering a newly installed shrub and a mature one.
Watering Requirements for Newly Planted Arborvitae
The first growing season is a vulnerable period as the plant must dedicate energy to establishing a functional root system in its new location. Transplant shock is common because the existing root ball cannot efficiently draw moisture to support the shrub’s full canopy. During the initial week after planting, water the root ball daily to keep it consistently saturated.
This frequency must quickly taper to encourage roots to grow out into the surrounding native soil. For the next three to four months, water two to three times per week, adjusting based on temperature and rainfall. Focus the water application directly on the original root ball and the immediate surrounding soil. The soil should feel consistently moist, similar to a wrung-out sponge, but never waterlogged or soggy.
Determining the Routine Watering Schedule (The ‘When’)
An Emerald Green Arborvitae is considered fully established after approximately two full growing seasons, at which point its watering needs transition from frequent establishment care to less frequent but deeper routine maintenance. Determining the correct frequency for an established shrub requires monitoring environmental factors rather than adhering to a strict calendar schedule. Local climate, including the amount of natural rainfall, ambient temperature, and soil type, dictates the actual watering frequency.
During the peak heat of summer and periods of drought, established arborvitae may require deep watering once per week to every ten days. Conversely, in cooler spring and fall temperatures, supplemental water is only needed during extended dry spells. The most accurate way to determine if water is needed is by physically checking the soil moisture four to six inches deep near the trunk. If the soil at that depth feels dry to the touch, it is time to water.
A particularly important time for watering is late fall, before the ground freezes solid for winter. This “dormancy watering” ensures the evergreen foliage has an adequate reservoir of moisture to draw upon throughout the cold months when the roots are inactive and cannot absorb water from frozen soil. Winter desiccation, or “winter burn,” is a common cause of browning in arborvitae and can often be prevented by this single, deep soaking before the onset of hard frost. This pre-winter hydration is especially necessary in regions that experience dry autumns or persistent winter winds.
Optimal Methods for Deep Watering (The ‘How’)
The primary goal when watering is to deliver water slowly and deeply to encourage the development of an extensive, deep root system. Light, frequent sprinkling is highly detrimental as it only wets the surface soil, causing shallow-rooted arborvitae to congregate roots near the top where they are highly susceptible to drought stress. A deep watering session should aim to saturate the soil to a depth of at least six to eight inches.
To achieve this depth, slow application methods are most effective, such as using a soaker hose, drip irrigation system, or a garden hose set to a low, trickling stream. These methods allow water to penetrate the soil profile gradually, minimizing runoff and fully hydrating the lower root zone. Positioning the water source at the base of the shrub and letting it run for an extended period, often thirty to sixty minutes depending on soil drainage.
A simple soil moisture test can confirm if the application was successful: insert a long probe or your finger into the soil several hours after watering. If the soil is moist at the six-inch mark, the watering was adequate. Overhead sprinklers should be avoided entirely, as they waste water through evaporation and wet the foliage, creating an environment conducive to fungal diseases. Applying a two-to-three-inch layer of organic mulch around the base of the plant helps retain soil moisture, keeping it several inches away from the trunk.
Troubleshooting Common Watering Problems
Identifying whether a browning Emerald Green Arborvitae is suffering from too much or too little water can be challenging because both issues present similar symptoms. However, the location of the browning often provides a helpful clue for diagnosis.
Underwatering typically causes the foliage to turn pale green or gray, eventually leading to a brittle, brown appearance at the tips and on the outer parts of the shrub. The entire plant may look generally wilted or stressed, indicating a systemic lack of hydration. For an underwatered shrub, the corrective action is an immediate and aggressive deep soak to rehydrate the root ball thoroughly.
In contrast, overwatering, which frequently leads to root rot, often causes the inner foliage near the trunk to turn yellow and then brown first. This yellowing progresses upward from the base as saturated roots lack oxygen and begin to die. The soil around an overwatered plant will feel permanently soggy or have a soft, squishy texture at the trunk’s base. If overwatering is suspected, cease all watering until the soil dries out significantly, potentially requiring improvements to soil drainage to prevent recurrence.