American Arborvitae (Thuja occidentalis)

American Arborvitae, Eastern White-Cedar, Northern White-Cedar

Northern white cedar (Thuja occidentalis) is a small- to medium-sized evergreen conifer native to North America, and can be found in a variety of environments, including forested wetlands and along cliffs. Essential oils are produced using northern white cedar, and it also finds use as an ornamental plant. Due to its increasing popularity in landscaping, more compact plants have been used to develop smaller strains.

I. Appearance and Characteristics 

Thuja occidentalis, also known as northern white-cedar, eastern white-cedar, or arborvitae, is an evergreen coniferous tree, in the cypress family Cupressaceae, which is native to eastern Canada and much of the north-central and northeastern United States. It is widely cultivated as an ornamental plant. It is not to be confused with Juniperus virginiana (eastern red cedar).

The name arborvitae is particularly used in the horticultural trade in the United States; it is Latin for ‘tree of life’ – due to the supposed medicinal properties of the sap, bark, and twigs. It is sometimes called white-cedar (hyphenated) or whitecedar (one word) to distinguish it from Cedrus, the true cedar.

Unlike the closely related western red cedar (Thuja plicata), northern white cedar is only a small or medium-sized tree, growing to a height of 15 m (49 ft) tall with a 0.9 m (3.0 ft) trunk diameter, exceptionally to 38 meters (125 ft) tall and 1.8 meters (5.9 ft) diameter. The tree is often stunted or prostrated in less favorable locations. The bark is red-brown, furrowed and peels in narrow, longitudinal strips. Northern white cedar has fan-like branches and scaly leaves. The foliage forms in flat sprays with scale-like leaves 3–5 millimeters (1⁄8–3⁄16 in) long.

The seed cones are slender, yellow-green, ripening to brown, 9–14 millimeters (3⁄8–9⁄16 in) long and 4–5 millimeters (5⁄32–3⁄16 in) broad, with six to eight overlapping scales. They contain about eight seeds each. The branches may take root if the tree falls.

Arborvitae trees can grow to be very old, and ancient trees have been documented. The currently oldest living specimen is 1,100 years old, and the oldest fossilized specimen has been documented to be 1,650 years old. The ages of these trees are confirmed by counting concentric circles within the bark of their trunks. The oldest trees grow on undisturbed cliff sides where they cannot be affected by wildfires or wildlife.

II. How to Grow and Care

Sunlight

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.

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.

Watering

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.

Soil

Plant arborvitae in moist but well-drained soil with a neutral to alkaline pH level. These shrubs do not like to be continuously doused in water so that their roots sit in soggy soil. Instead apply a heavy layer of compost or mulch over the root zone each year. Keep to a regular watering schedule, and the mulch will help to preserve soil moisture.

Fertilizing

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. For the amount to use, follow product label instructions.

Planting Instructions

When to Plant

Plant arborvitae in the fall to avoid heat stress and give its roots time to establish before winter arrives.

Where to Plant

Plant emerald green arborvitae in moderately moist, well-drained soil in full sun or partial shade (in warmer climates, some shade is preferable). Remove weeds, grass, rocks, and debris.

How to Plant Emerald Green Arborvitae

  • Remove the burlap wrapping around the root ball or carefully pull the root ball out of the container and loosen some of the roots.
  • Plant the root ball in a hole twice as wide and as deep as the root ball. Keep the top edge of the root ball level with the surface.
  • Fill in the soil around the root ball. When you are halfway done, water thoroughly.
  • Finish filling the hole and pack it down with your hands. Water thoroughly from the surface level.
  • Add two inches of mulch to the surface. Do not allow the mulch to touch the stem.

Pruning

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.

Overwintering

Arborvitae are cold-hardy but can benefit from extra winter care, especially when young. Snow and ice can cause stem breakage. Periods of drought, high wind, and plunging temperatures can cause drying out and browning. Mulch can also keep the roots insulated and retain moisture in the ground.

To preserve the stems, tie them with twine. Or, for even more protection against hungry deer, wrap it with burlap around a circle of stakes. Burlap wraps are recommended if you live in zone 2.

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 resin oozing from the trunk or branches. Remove the affected branches. If the trunk is affected, the tree may not survive.

Common Problems 

‘Emerald Green’ arborvitae are low maintenance, cold hardy, and generally have fewer problems with pests and disease.

Browning Leaves in Winter

Arborvitae are winter hardy, and ‘Emerald Green’ should stay green throughout the year, but they may lose a little of their vibrancy. They are susceptible to browning when the temperatures suddenly plunge or lack water in winter. Keep giving water in the winter if the soil dries out or if there is a lack of rain or snow.

Dropping Needles

Each year, arborvitae will drop their needles from the plant’s interior. It may look like the entire plant is browning from the inside out. This browning is natural and expected. The needles may start to pile up along the interior stem or trunk of the plant. Clean them out to prevent rot from spreading from the decomposing pile of needles.

Loss of Foliage From Top Down

Bagworms defoliate arborvitae, usually starting at the tree top and working their way downward. These caterpillars eat leaves, create telltale “egg bags,” and leave bare branches in their wake. Left alone, they can kill the plant. To remedy the situation, remove all the bags. If it’s a bad infestation, you might need a pesticide. Neem oil is an organic pesticide alternative that will kill bagworm larvae.

III. Uses and Benefits 

Thuja occidentalis is commercially used for rustic fencing and posts, lumber, poles, shingles, and in the construction of log cabins. It is the preferred wood for the structural elements, such as ribs and planking, of birchbark canoes and the planking of wooden canoes.

The essential oil within the plant has been used for cleansers, disinfectants, hair preparations, insecticides, liniment, room sprays, and soft soaps. The Ojibwa reportedly made a soup from the inner bark of the soft twigs. Others have used the twigs to make teas to relieve constipation and headache.

Eastern white cedar – as arborvitae – is a popular ornamental plant used in both residential and commercial landscapes.

Thuja occidentalis has important uses in traditional Ojibwe culture. Honored with the name Nookomis Giizhik (Grandmother Cedar), the tree is the subject of sacred legends and is considered a gift to humanity for its myriad of uses, among them crafts, construction, and medicine. It is one of the four plants of the Ojibwe medicine wheel, associated with the north. The foliage is rich in vitamin C and is believed to be the annedda, which cured the scurvy of Jacques Cartier and his party in the winter of 1535–1536. Due to the presence of the neurotoxic compound thujone, internal use can be harmful if used for prolonged periods or while pregnant.

American Arborvitae (Thuja occidentalis) Details

Common name American Arborvitae, Eastern White-Cedar, Northern White-Cedar
Botanical name Thuja occidentalis
Plant type Native Plant
Hardiness zone 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b
Growth rate Slow
Harvest time Summer
Height 40 ft. 0 in. - 60 ft. 0 in.
Width 40 ft. 0 in. - 60 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Leaf color Gold/Yellow