The Mighty Arborvitae

We see them everywhere, but most of us take little notice of this ubiquitous evergreen—the American arborvitae (Thuja occidentalis). Also known as white cedar, the common name arborvitae is from a French phrase that means "tree of life." Indigenous people of North America and Canada introduced early settlers to its medicinal properties—a tea made from the foliage could ward off scurvy. Native peoples also used the wood for canoe frames. As one of the Northeast's native evergreen conifers, arborvitae bears closer examination for its wildlife value and uses in the landscape.

Arborvitae Appearance

In its natural form, arborvitae Thuja occidentalis are tall, dense, columnar-shaped trees often planted in a row. The leaves are flat, scaly, and arranged in fan-like clusters; they give off a pleasant citrusy scent when crushed. Small cones appear in bunches near the ends of the branches. Arborvitaes were commonly used in the landscape in the mid-twentieth century, and their longevity is one of the reasons we see so many today. They have somewhat fallen into disfavor because their foliage tends to thin as they age, and their natural height of 50 to 60 feet can become unmanageable in residential gardens.

Fortunately, many arborvitae cultivars have been developed to fill niches in the landscape and circumvent some of the problems of the natural, native arborvitae. Here are some popular options:

'Emerald Green' was one of the first cultivars of the American arborvitae, introduced in Denmark, where it is known as 'Smaragd'. It improves on the straight species of arborvitae as it is more compact, about 3 to 4 feet in diameter, and features a deep green color that does not dim in winter.

'Techny' or 'Mission' has dark green foliage year-round and is well-suited for northern winters. It has a pyramidal form and makes an excellent hedge.

'Green Giant' is a hybrid cultivar of the giant western arborvitae (Thuja plicata), native to the northwestern United States and western Canada, and the Japanese arborvitae (Thuja standishii) native to Asia. It is fast-growing and can reach a height of 50 to 60 feet. This cultivar can be planted to form a giant hedge or as an impressive, featured specimen. Despite the name, its foliage fades to bronze in winter.

'Steeplechase' is another hybrid cultivar of arborvitae (T. plicata x T. standishii). It is more compact than 'Green Giant', with a spread of about 8 feet and growing to 20 to 30 feet.*

Keep an eye out for small, ball-shaped arborvitae varieties, including Thuja Tater Tot®, Mr. Bowling Ball®, and Anna's Magic Ball®, which has golden-green foliage.

Use in the Landscape

Arborvitaes' dense foliage and fast-growing habit have made them popular choices for hedges. Varieties such as 'Emerald Green' and 'Steeplechase' have a compact, pyramidal shape that makes a desirable accent in the landscape. Small, ball-shaped varieties lend themselves to landscape borders and containers.

Of course, the closer the variety is to its natural form, the more supportive it is to wildlife. Arborvitaes provide shelter and a nesting spot for many native bird species, who also feed on seeds from the cones. Their foliage is eaten by rabbits and deer, which can be a mixed blessing for the gardener (more on deer resistance below).

Arborvitae Care

Arborvitaes grow best in full sun, though they can take some light shade. They prefer moist, well-drained soil but have been known to adapt to poor soil and rocky conditions. They are not drought-tolerant and may need irrigation during dry spells. Unlike many conifers that require acidic soil to thrive, arborvitaes can tolerate a slightly acidic to alkaline pH (6.0 to 8.0).

If planning on growing arborvitaes as a hedge, carefully consider the spacing requirement of the chosen variety. Even though you may be anxious for them to fill in and form a screen, each tree needs enough room to develop a healthy root system.

An annual light shearing of the arborvitae is the best way to keep its size in check if desired. This is particularly advisable if you want to keep the top of a hedge at a manageable height.

Common Arborvitae Problems

Though an enduring native tree, the arborvitae is not without its weaknesses.

Ice, Snow, and Wind Damage

Native arborvitaes' branches tend to break when weighed down with snow and ice. Cultivars have been bred to be less susceptible to this damage. And even though arborvitaes are often planted in rows, most varieties do not make a suitable windbreak; winter wind especially can cause browning foliage. 'Green Giant' may be the most suitable variety as a windbreak.

Deer Browsing

The same qualities that make arborvitae appealing as a native plant also make them susceptible to damage from deer browsing. If deer often visit your property, arborvitae is probably not the plant for you. 'Green Giant' is known to be somewhat deer-resistant.

Insect Pests

Bagworms are probably the most prevalent pest of arborvitae. An infestation looks like small, brown cones hanging from the branches—these are the cocoons of the bagworm, which is actually a caterpillar. If left unchecked, bagworm feeding can defoliate arborvitae; most of the year's damage is done when you see the cocoons in late summer. The simplest control for bagworms is to remove and destroy the "bags." You can also spray the tree in June when the young bagworms are crawling and are not protected by their cocoons. Bacillus thuringiensis (Bt) is a good insecticide choice for this pest because it targets the caterpillar family.

Other pests visiting your arborvitae include leaf miners, mealybugs, scales, and spider mites. If you decide to treat your tree with an insecticide, be sure it is designated for the correct plant and pest, and always follow label directions.

Browning

Arborvitaes shed bits of older foliage when deciduous trees drop their leaves in autumn. As part of this natural process, the oldest branches of the tree will brown and fall off. Arborvitaes are also affected by tip blight diseases, which cause tan foliage and dead branches at their worst. If you have questions about whether your arborvitae's imperfections are natural or the beginning of a disease or pest attack, consult your county's Master Gardener Garden Hotline.

Do not overlook the arborvitae when choosing a plant for your garden. They are an excellent option for screens and hedges. Plus, they can provide a backdrop to colorful perennials or a garden focal point. Those who add arborvitae to their landscape can take satisfaction in the knowledge that they support wildlife by planting a non-invasive, native species.

*Even though some popular arborvitae hybrid cultivars are related to Thuja plicata, native to western North America, they still have some of the same wildlife sheltering qualities as the northeastern Thula occidentalis and have not become invasive.