Black Hemlock Tsuga mertensiana

Mountain hemlock is a medium-sized needled, coniferous, evergreen tree that has a narrow width but can mature to heights of 30 to 100 feet. It has a conical or pyramidal crown, dense foliage, spreading branches, and the leading shoot may be tilted. The bark is grayish-black to reddish-brown and is fissured and scaly. The greenish-blue to silver-green needles are the same lengths and dense on all sides with a bottle brush effect. The seed cones are purple and then ripen to a grayish-brown. Mountain hemlock is a member of the Pinaceae or pine family.

The mountain hemlock is native to the southeast coasts of Alaska and British Columbia. It is also native to the mountains of the States of Washington, Oregon, the high Sierras of California, and the high Sierras of Nevada. It can be found in parts of Idaho and Montana. It typically is found at higher altitudes in the United States. In subalpine areas, the tree may only reach a height of 10 feet; however, in lowlands, it may reach a height of 100 feet. The tallest known trees have reached 175 feet. and the oldest trees are 500 to 1400 years old.

The genus name, Tsuga, originated from the Japanese word "tsu-ga," which means "tree" and "mother." The species name, mertensiana,  is named in honor of a German botanist, Franz Karl Mertens.

The mountain hemlock prefers full sun and moist, cool summers. They do not perform well in the southeastern United States due to their intolerance to the heat. The tree may be propagated by seedlings, cuttings, and layering

The trunks of the tree are flexible and can withstand the weight of snow for months in alpine regions.  After the snow melts, the tilted trees will upright themselves. The mountain hemlock is less tolerant to shade than the western hemlock. Squirrels eat the seeds from the cones, and grouse like to forge on the buds and leaves.

This tree does best in areas where the growing season is short, and the winters are cold and long. When the mountain hemlock is young, it may be pruned as a hedge. 

Quick ID Hints:

• branches raise upward at the tips
• needles are of equal length, dense on all sides of the stems in a bottle brush effect
• cones are narrow and long, measuring about 3 inches long and 1 inch wide

Pests, Diseases, and Other Plant Problems:  The mountain hemlock has no serious disease or insect problems. Hemlock adelgid may be found on the foliage and will appear as white cotton tufts. Trees that are heavily infested will need to be removed.

VIDEO created by Ryan Contreras for “Landscape Plant Materials I:  Deciduous Hardwoods and Conifers or Landscape Plant Materials II:  Spring Flowering Trees and Shrubs” a plant identification course offered by the Department of Horticulture at Oregon State University