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American Arborvitae

Posted: April 17, 2014

Learn more about the features of American arborvitae (Thuja occidentalis).

There are three conical evergreens you can find in "wild" Pennsylvania. Because they are uniquely tight evergreen and conical, they are more likely found in towns, residential communities, and cemeteries.

The beautiful three are Atlantic cedar (Chamecyparis thyoides), Eastern red cedar (Juniperus virginiana), and American arborvitae (Thuja occidentalis). As you have already noticed, while the generic names sound similar, the scientific names are very different.

If you had the seed bearing structures of each, (side-by-side) you would see that Atlantic cedar has a small round soccer ball shaped cone - when the peltate scale opens, it is fastened in the center to the cone. The Eastern red cedar has a small rounded blue berry looking fruiting body that has been used for flavoring gin. The arborvitae has a small (ten scales), cone-like structure that appears in upright clusters. Later in the year the clusters become a dirty weathered gray and droop downward. These scales bear only about eight seeds and are soft, not "pine-cone" hard. The male cones and female cones occur on different branches but on the same tree.

All of the above have a special fragrance if the foliage is crushed and sniffed!

Speaking of sniffing - I recall my Wood Technology lab class where we had to identify all of the "cedar" wood blocks by smell: Port Orford, (arrow shafts), Incense cedar (pencils), Northern white cedar and Southern white cedar (which are both now called Atlantic white cedar), Eastern red cedar (from which they make the red and white wood boxes and cedar chests), and Western red cedar. It is interesting to note that none of these are actually cedars since that honor goes to those in the genus Cedrus as in Deodar cedar and cedar of Lebanon. (Still with me?)

Now as for the Arborvitae - (also called White cedar, Eastern white cedar, Northern white cedar, Eastern arbor vitae, or Swamp cedar) it is browsed heavily by deer until a “browse line shape” is achieved and then it rises from there. It is also broken by heavy snow-loads. The killer insect is bagworms, which usually start at the top and work their way down. It was one of the first American imports to Europe, but it doesn't grow half as well there as it does in North America.

Horticulturally, Arborvitae has been listed by Bailey as having one hundred cultivars, fifty to eighty by Dirr, and at least fifty are found commercially and about ten are very popular. They grow straight up and are used for hedge rows. Some are gold or gold-tinged; some are dwarf; and several are globe shaped. I notice that the "globes" tend to fall apart in old age but if left in the landscape become quite interesting as non-globes.

Botanists don't list “wild” finds very often, since they think that they are escapes from nurseries or home landscapes. Apparently there is no botanical record of groves of arborvitae in Pennsylvania's primeval forests. My guess is that since they only grow six foot tall, if they are not growing in a wetland or a grazed prairie, would soon be overtopped, suppressed, then dead. In the West the giant arborvitae (Thuja plicata) is reported to grow to one hundred feet.

Just last month, I measured an American arborvitae with a height of sixty-four feet, a spread of thirty-five feet, and a trunk diameter of forty inches, making it the new largest arborvitae in Pennsylvania. You can find it in the Garden of Memories Cemetery opposite the Hoffman Zion Church just south of Jenner's Crossroads in Somerset County. The national champion grows in Alleghany County, Virginia.

Just a note: There is a beautiful fan-branched compact Oriental Arborvitae (Thuja orientalis), which I found to grow at least thirty feet tall in Latrobe, PA.

By William C. Paxton, Landscape Architect and Consulting Forester