WSU Clark County Extension

PNW Plants Searchable, categorized images

Mountain Hemlock

Scientific name: Tsuga mertensiana

Type:Coniferous trees
Plant Requirements
Zone:5 to 8
Plant Characteristics
Height:30 ft
Width:15 ft
Additional Characteristics



Wildlife value

Description While long known as true Northwest Cascades native, growing to height of 60-100’ (but very narrow in width), this hemlock is also grown as a yard ornamental for gardeners looking for a tough, slow growing pyramidal conifer with tight foliage.

This is an evergreen tree bearing flattened, single needles, spirally arranged around the limbs. Needles are short (1/2” to 3/4") and thickened in cross section, uniform in color on all sides ranging from dark green to blue-green, and have rounded apexes with short distinctive petioles. They cover the branches densely on all sides (bottle-brush effect) or may be mostly upturned. Needles on mountain hemlock are equal in length, western hemlock (Tsuga heterophylla) are un-equal in length.

Seed cones are light to deep purple (sometimes green), narrow at each end and longer than those of western hemlock. They attain a length of approximately one inch.

With regular moisture and part-shade, mountain hemlock will not only grow to become a prized native to higher elevations of California to Alaska, but also as a landscape plant as well. It seems to grow well on a wide array of sites. It thrives where the growing season is short and winters are long and cold. When the trees are young, gardeners often shear them into sheared hedges.

Hemlock adelgid can be a problem on sheared hedges where air circulation has been reduced. Look for the white, cottony encrustation on the bark, and the white tufts on the needles. Once severely infested, these plants generally have to be removed.
For assistance, contact Dr. Charles Brun (, (360) 397-6060 5701
Computing and Web Resources, PO Box 6234, Washington State University, Pullman WA 99164-6234