The Green Giant Arborvitae (Thuja ‘Green Giant’) is a widely favored choice for creating dense, fast-growing privacy screens. Its rapid growth rate and columnar form make it highly desirable for homeowners. Following installation, the successful establishment and long-term health of this evergreen depend on a precise and consistent watering regimen. Focusing on the immediate post-planting period is the most significant factor determining whether the tree will survive and thrive.
The Critical First Month: Establishing the Root Ball
The period immediately following planting is when the tree is most vulnerable. Immediately after backfilling the hole, a thorough, deep soaking is necessary to settle the soil and eliminate air pockets around the roots. This initial saturation should be equivalent to applying approximately 10 gallons of water per tree, ensuring the entire root mass is moistened.
For the first seven days, the newly planted arborvitae requires daily watering to ensure the roots do not dry out. This daily application should be lighter, focusing on maintaining consistent moisture within the original root ball. Moving into weeks two through four, reduce the frequency to every other day, encouraging the tree to seek moisture further afield.
The goal during these initial weeks is to keep the root zone consistently moist, but never soggy, to facilitate new root hair growth. A slow, steady application is preferable, such as using a soaker hose or setting a garden hose to a pencil-thin stream for about ten minutes per tree. This slow watering ensures the moisture penetrates deeply into the root ball rather than running off the surface.
Monitoring Soil Moisture and Plant Health
Relying solely on a fixed schedule can lead to drought or waterlogging, necessitating regular physical checks of the soil moisture content. The simplest method, the “finger test,” involves inserting a finger 2 to 3 inches deep directly into the soil of the original root ball. If the soil at that depth feels dry, it is time to water; if it feels cool and moist, watering should be delayed.
Observing the foliage provides further clues about the tree’s condition. Underwatering typically causes the needles to brown at the tips or the overall foliage to droop slightly as the plant conserves moisture.
Conversely, overwatering is a common cause of failure in new plantings. Excessive saturation leads to root suffocation, causing the foliage to turn yellow or light green as the roots struggle to take up nutrients. If the soil remains muddy or mushy several hours after watering, the frequency or duration must be immediately reduced to prevent root rot.
Transitioning to Seasonal Maintenance
After the intensive first month, the tree enters a gradual tapering period that continues for the rest of the first year.
Months Two and Three
For the second and third months, reduce the watering frequency to two or three times per week. Maintain the deep watering technique to encourage roots to grow outward into the native soil. This decrease in frequency promotes a stronger, more expansive root system.
Months Four Through Six
During months four through six, reduce the frequency further to a single deep watering event per week, provided there is no significant rainfall. The shift from frequent, shallow watering to less frequent, deep watering is a strategy to establish drought tolerance by compelling the roots to seek moisture deeper in the soil profile. This deep watering should saturate the top 12 to 18 inches of soil each time.
After the First Year
Once the arborvitae has completed its first full growing season (about 12 months), it is considered established. A fixed watering schedule is no longer necessary, and the tree should rely on natural rainfall. Irrigation is only required during extended periods of drought, defined as two weeks or more without significant precipitation, or when the foliage shows signs of stress.
When supplemental watering is needed in subsequent years, it must be a deep soaking that mimics a heavy rain event. Providing a large volume of water infrequently is more beneficial than small, frequent sprinklings, which only encourage shallow root development.
Environmental Factors that Alter the Schedule
The general watering guidelines must be adapted based on the specific characteristics of the planting site. Soil composition significantly impacts drainage and retention, requiring adjustments to the standard schedule.
Soil Type
Clay soils retain water well and necessitate less frequent watering to avoid waterlogging and root rot. Conversely, sandy soils drain rapidly, requiring more frequent applications of water, though the volume per session may remain similar.
Heat and Drought
Periods of extreme heat or prolonged drought increase the tree’s transpiration rate, accelerating moisture loss through the foliage. This requires a temporary increase in watering frequency.
Winter Preparation
Winter preparation requires a specific late-season watering protocol, even when the tree is dormant. Evergreen foliage continues to lose moisture throughout the winter, so a deep soaking in late fall, before the ground freezes solid, is necessary to prevent desiccation. Active watering must continue until the soil temperature drops consistently below freezing, as the roots can no longer absorb moisture below that point.