What's the Growth Rate of Mountain Hemlock?

Identification

• Native to the Pacific Northwest Cascade Range, mountain hemlock is winter hardy to U.S. Department of Agriculture plant hardiness zones 5 through 8. It is a densely needled evergreen with uniform color, ranging from blue-green to dark green in appearance. Needles cover branches all the way around, forming a bottlebrush effect, or sometimes grow mostly upright. The cones are purple to light green, usually about 1 inch long and narrow at one end.

Growth Rate

• Mountain hemlock is a slow-growing tree, which means it adds 12 inches or less to its height in a single growing season. In gardens, it usually reaches a height of around 30 feet, although in the wild, it can reach 100 feet or more. Its narrow width gives it a tight, pyramidal formation. Mountain hemlock should not be confused with the Western hemlock (Tsuga heterophylla), also hardy to USDA zones 5 through 8, which has looser foliage and generally grows much taller -- to 100 feet -- in the home garden.

Culture

• Mountain hemlock prefers regular moisture and partial shade for best growth. Water it weekly to ensure ground moisture is not taken by ornamentals that are already present. After two months, relax the watering schedule and only give it as much as you give the rest of the garden. Mountain hemlock grows on a wide array of sites and will tolerate shearing quite well when young and can be used as a hedge plant. Watch out for hemlock adelgid, which can infect sheared hedges and forms a white crust on bark and tufts on needles; remove infected branches and increase air circulation to combat and prevent this disease.

Garden Uses

• Mountain hemlock works best as an ornamental plant, growing either alone as a specimen or grouped as a screen, where tight foliage will offer both privacy and windbreaks. It is also a good addition to higher-elevation native gardens all along the West Coast of the United States and into Alaska. Although the tree is tolerant, it is not a good choice for dry, exposed gardens, where it will become thin and unhealthy.