Emerald green arborvitae is best planted in the fall when it will experience minimal heat stress. Its foliage consists of flat sprays of glossy bright green needles, plus urn-shaped cones about an inch long that turn reddish-brown in the fall. Most specimens grow at a fast rate early on and slow down as the tree matures, reaching 7 to 15 feet high, and possibly reaching 20 feet. Occasionally, this plant is pruned to form spiral topiaries. The tree is toxic to humans and animals. For the most successful tree, plant emerald green arborvitae in moderately moist, well-drained soil in full sun or partial shade (in warmer climates, some shade is preferable). Leave 3 to 4 feet between each tree if you are planting as a privacy fence or screen. Heavy snow can break branches, so brush them off after a storm—broken limbs should be pruned off, and the plants may need to be staked upright until they recover.
Light
Emerald green arborvitae should be grown in full sun or partial shade. They generally need at least six hours of sun daily, but too much direct sunlight can stress the plant and burn the foliage. However, they should not be planted in full shade either, since this can greatly reduce the density of the foliage.
Soil
Plant arborvitae in moist but well-drained soil that boasts a neutral to alkaline pH level. These shrubs do not like to have their roots in soggy soil, so apply a heavy layer of compost or mulch over the root zone each year to preserve soil moisture.
Water
Your arborvitae will need watering twice weekly for the first few months after planting, then weekly watering (about 1 inch of water) for the next year or so. Once established, make sure it gets about a half-inch of water weekly, either through rainfall or irrigation.
Temperature and Humidity
Emerald green arborvitae does better in cooler, dryer climates. In very humid conditions, fungal diseases can be a problem. To help prevent this, plant your trees at least 3 to 4 feet apart from one another in order to improve air circulation. Avoid exposed, windy locations, especially in colder climates.
Fertilizer
Arborvitae plants normally do not need feeding. However, if new growth is very sparse or slow, an application of a balanced fertilizer containing all major nutrients is recommended.
Pruning Emerald Green Arborvitae
If desired, light pruning in the early spring can help your arborvitae remain neat and foster thicker growth. To do so, trim the leafy parts of the branch, making sure not to cut back to bare wood. Dead or diseased branches should be removed to prevent decay and improve air circulation. In addition, you may prune your tree to maintain the natural shape of the shrub, which is wider at the bottom and tapering inward toward the top. Especially adventurous gardeners can even prune the shape to form spiral topiaries.
Common Pests and Plant Diseases
Arborvitaes are rarely troubled by insect and disease problems. Bagworms may feed on the foliage of arborvitaes. Control them by handpicking the egg bags and destroying them before the insects hatch. Spider mites can also do damage to the trees. The plant can sometimes suffer from needle and twig blight caused by fungi, especially if air circulation is poor. To control blight, prune off all affected branches and treat them with a fungicide. Keep an eye out for stem canker, a fairly serious fungal disease that causes lesions, sores, and sticky oozing resin from the trunk or branches. Remove the affected branches. If the trunk is affected, the tree may not survive.
