Thuja occidentalis is better known as Arborvitae. This conical-shaped evergreen grows to a height of 20 feet, with a 10-foot spread. Its leaves are small and scale-like. It prefers a higher level of humidity than some other evergreens, making it a good choice for wet climates. It prefers moist, deep, loamy soil and is very adaptable and tolerant once established. In dryer locations, the Thuja may need supplemental watering.
Establish a healthy root system during the first year for your Thuja. When planting Thuja, dig a hole at least twice as wide as the root ball using a shovel. If your soil is dense with clay or very sandy, mix the soil with equal parts well-rotted compost and peat moss. This will improve drainage, retain moisture and improve root respiration. When refilling the hole around the tree, use a garden hose to moisten the soil you are replacing.
Create a water well around the root ball after the tree is planted. Using dirt left over from the planting hole, build a 3-inch-high by 4-inch-wide ring around the perimeter of the planting hole. Pack the dirt firmly so the ring creates a dam around the plant's perimeter. This will direct water out to the edges of the hole and encourage the roots to expand in search of water.
Surround the planting hole with a soaker hose or use a misting garden hose attachment to apply a steady, even stream of water to the soil. Water for a minimum of one hour once or twice a week, depending on the temperature and rainfall. Spring- and fall-planted trees will need less watering than those planted in mid-summer.
Mulch newly planted Thuja to retain moisture and deter weeds. Apply a 2- to 3-inch layer of shredded cedar bark or root mulch around the base of the plant. Leave a 2-inch ring around the diameter of the trunk to allow for airflow and to discourage rodent damage.
Decrease watering frequency after the first growing season. Established Thujas like an evenly moist--but not soaking--soil. Place a rain gauge (available in most hardware and home centers) near your tree, and allow natural rainfall to collect in the vial. Read the measurement on the beaker to determine if your Thuja is getting its weekly requirement of 1 inch of water. Supplement as needed with a soaker hose, sprinkler or drip irrigation system. Water continuously into the fall.