American Arborvitae

by Jan Cashman

In the middle of winter, the green foliage of evergreens gives us color in an otherwise colorless time of the year. One of these evergreens, American arborvitae, is a dense, compact shrub native to northeastern North America. As you can see from the photo, arborvitaes are beautiful in the winter (and summer, too). With a name like arborvitae (which means ‘tree of life’), one would think that would be the botanical name for this plant, but arborvitae is the common name, along with “cedar”. Thuja occidentalis is the botanical name.

Until 50 or 75 years ago, arborvitaes were the commonly used evergreen for foundation plantings in the U.S.; more recent evergreen introductions, like dwarf spruce and pines are starting to replace arborvitaes. American arborvitaes have been used in European landscapes since they were brought from North America hundreds of years ago. Their tightly sheared shape lends itself to formal European gardens.

There is another species, T. orientalis, that is not hardy in the North, but often planted in the southern U.S. Some varieties of this species have unusual blue or yellow foliage. Giant arborvitae (species T. plicata) is native from northern California to Alaska, and is found in Glacier Park; it reaches almost 200 feet in height. This large tree is an important source of cedar shingles and siding.

Many cultivars of Thuja occidentalis have been selected by growers over the years for their different shapes and foliage. Pyramidal arborvitae, a tall (15′), narrow (4′) variety that needs little pruning, has been one of the most planted of the arborvitae. While Cashman Nursery uses pyramidal arborvitae in the landscapes we design, pyramidal arborvitae does have a tendency to winterburn during our sunny winters. It does best planted in sheltered locations here, on north or east exposures. The Delaney’s historic home on South Willson has newly planted emerald arborvitae, a variety similar to pyramidal, surrounding their yard inside their wrought iron fence. The formal shape of these arborvitae compliment the historic brick house. As these plants grow, they will provide privacy for the Delaney’s interior yard.

Probably the best arborvitae cultivar for our climate is ‘Techny’, also known as Mission arborvitae, because it was discovered at Mission Gardens in Techny, Illinois. Techny is not as narrow as pyramidal arborvitae; it grows to about 15 feet in height and 6 feet or more in spread. Its dense, dark green foliage is resistant to winterburn. We planted a row of Technys in 1977 to screen Springhill Road from our house. By pruning them every other year, they now provide a beautiful, tall, impenetrable screen. Another example of Techny arborvitae can be seen on the west side of Holy Rosary Church off Main Street. Take a look when you drive by; their formal shape is a perfect accent to the majestic church building.

Techny arborvitae can be easily pruned into a globe shape when desired. A few new cultivars have been introduced lately that have the qualities of Techny, but grow slower so don’t require as much pruning. One is ‘Technito’. Siberian arborvitae, which grows into a rounded shape, is hardy and resistant to winterburn, but its foliage is courser than Techny.
Arborvitaes are native in climates more humid, cloudy, and wet than ours; they like moist, well-drained soil. Most varieties benefit from pruning once a year to keep them dense – June is the best month to do this, just when the new growth is emerging. “Give them a haircut” as Jerry’s father used to say.

Unfortunately, arborvitaes are susceptible to spider mites, a tiny red spider that sucks the chlorophyll from the needles in the summer. If the infestation is severe enough, spider mites can greatly weaken your arborvitae. Use a hoze nozzle to wash off your arborvitae in mid-summer when spider mites are active. If this doesn’t control them, spray with an insecticide such as malathion or Isotox; multiple applications may be necessary.

Deer love to eat arborvitae, so if you have deer in your yard, this may not be the plant for you. We fence all of our arborvitae in the winter to keep the deer from them. In the summer, the deer leave them alone because there is so much other food around.

If you are looking for a dense, easily prunable, formal evergreen for around your home, consider one of the American arborvitae varieties. They are beautiful winter and summer!