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Plant Answer Line Question

Keywords: Plant longevity, Osmanthus

What is the lifespan of Osmanthus? A client's 20-year-old, 12 ft. tall shrubs were once a hedge that one was unable to see through, but have become a walk-through wall these past couple of years.


According to SelecTree, a database produced by the Urban Forest Ecosystems Institute, most Osmanthus species have a longevity of 50 up to 150 years. A plant's lifespan varies, and urban trees and shrubs tend to be subjected to more interventions in the form of pruning, pollution, damage from construction, and so on. Also, the hedge has undoubtedly become woody with age.

Date 2018-05-04
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Plant Answer Line Question

Keywords: Thuja occidentalis, Plant longevity, Thuja

What is the typical life of an arborvitae tree?


Arborvitae is the common name of Thuja, usually Thuja occidentalis. As with human beings, lifespan can only be an estimate, due to various circumstances which affect health and longevity. Urban growing conditions differ from those experienced by plants growing in the wild, for example. An article in The International Journal of Plant Sciences, Vol. 153, No. 1 (March 1992) by P. E. Kelly, et al. suggests that T. occidentalis growing on cliffs of the Niagara Escarpment in Ontario, Canada could be over 1,000 years old.

The record for this tree in the Urban Forest Ecosystems Institute database, SelecTree, indicates that its lifespan ranges from 40 to 150 years. Columnar arborvitae, Thuja occidentalis 'fastigiata,' is listed as having a lifespan of 50 to 150 years.

The Lady Bird Johnson Wildflower Center provides more information on Thuja occidentalis, too. Here is an excerpt:

"In a crowded environment, this tree is slender and not well-branched. In the open, it improves in form and density. The evergreen can be single- or multi-trunked and columnar or conical in shape. Eastern arborvitae can grow 40-60 ft. tall, but under cultivation will probably be no taller than 30 ft. Branches end in flat, spreading, horizontal sprays of fragrant, dark-green foliage which turns yellow-green or slight brown in winter. Resinous and aromatic evergreen tree with angled, buttressed, often branched trunk and a narrow, conical crown of short, spreading branches.

Probably the first North American tree introduced into Europe, it was discovered by French explorers and grown in Paris about 1536. The year before, tea prepared from the foliage and bark, now known to be high in vitamin C, saved the crew of Jacques Cartier from scurvy. It was named arborvitae , Latin for tree-of-life, in 1558. The trees grow slowly and reach an age of 400 years or more."

An article from the May 2002 issue of the Journal of Arboriculture lists Thuja occidentalis as a long-lived tree with a medium growth rate. They define "long" as over 200 years. However, most arborvitae one sees in urban landscapes would be unlikely to survive that long, due to many variables (poor planting methods, overcrowding, pollution, exposure to lawn chemicals, etc.).

Date 2017-06-09
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Plant Answer Line Question

Keywords: Fraxinus latifolia, Plant longevity, Populus balsamifera ssp. trichocarpa

Do you know which type of cottonwood tree is growing along shores of Lake Sammamish, and the normal life expectancy is for these trees? Someone told me they are "blackheart cottonwoods." Is that true?

We also have Oregon swamp ash growing here. Are these trees really just indigenous to Oregon, and what is their life expectancy?


I could not find any reference to "blackheart cottonwood," but here is information about black cottonwood (I cannot be sure these are the trees you have around Lake Sammamish). Populus balsamifera ssp. trichocarpa (its botanical name) is native from southern Alaska to northwestern Mexico, according to Arthur Lee Jacobson's Trees of Seattle (2006). It has a relatively short life span (and probably shorter in urban and suburban settings than in the wild) of 100-250 years. These trees have brittle limbs, and sometimes fall prey to strong winds. Jacobson mentions several hybrid cottonwoods, one of which closely resembles the native species but is crossed with a northeast Asian species, P. maximowiczii.

Just to complicate things, there is another Populus whose common name is black poplar (Populus nigra) and it is native to northwest Africa, Europe, western Siberia, and the Caucasus. There are many varieties of this Populus as well.

The USDA and CalFlora have information about black cottonwood for you to compare with the trees around the lake. Compare and contrast with the USDA page on black poplar.

As for the longevity of these trees, see what Arthur Lee Jacobson says about old trees. Here is an excerpt:
"Frequently the oldest trees are not the largest, so it is not as simple as finding the biggest trunk. Cottonwoods grow gigantic in a hurry, then bust up, earning their nickname rottenwood."

Arthur Lee Jacobson has led tours of the trees on the Sammamish River Trail, and he is the best-versed person locally on what trees are growing in our area, so you may want to contact him directly.

As for Oregon swamp ash, there are trees called Oregon ash, and trees called swamp ash, but I could not find a tree called Oregon swamp ash. Oregon ash is Fraxinus latifolia, and is a Northwest native whose range also extends to southern California. According to Jacobson's book, it closely resembles green ash (Fraxinus pennsylvanica), except that the native species has bark which flakes easily from the trunk, leaflets of 7 (rather than 9) which are hairy, rounded and broad. Its seeds are broader than green ash.
The USDA Forest Service has detailed information as well. Below is an excerpt:
"Oregon ash has moderately rapid growth for 60 to 100 years and attains a height of 18 to 24 m (60 to 80 ft) and a d.b.h. of 40 to 75 cm (16 to 30 in) in 100 to 150 years on good sites. Individuals may grow twice as large and reach 200 to 250 years of age under favorable conditions, although they generally grow slowly after their first hundred years."

The website SelecTree says Oregon ash trees usually live over 150 years.

Swamp ash is also known as black ash, or Fraxinus nigra, and is native to the northeastern swampy woodland areas. They are not mentioned in Jacobson's book or in other local sources, so I suspect they are uncommon in our area. Here is a link to the Forest Service description of this tree.

Date 2018-03-07
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May 31 2018 13:14:08