Tall, shade-tolerant evergreen with soft, flattened needles, bright green when new, then lustrous dark green and whitened on the lower surfaces. Resistant to the hemlock woolly adelgid. Availability limited but expected to increase in the near future.

Description:

Tall, shade-tolerant evergreen with upright, pyramidal stature supports branches that are slightly more pendulous than those of other hemlocks. The cinnamon-color bark is furrowed and attractive. Foliage color ranges from light green/yellow on new growth to dark green on older growth. The cones are somewhat pendulous, small (compared to pine or spruce cones), and usually abundant. The Western hemlock will grow to 40- 60 feet in the east. The Western hemlock is native to the western U. S. where it is an important tree in the timber industry. It grows extremely rapidly in its native habitat but more slowly on the east coast

Landscape Use:

Use as a stately specimen in areas at least partially protected from sweeping winds. They also can be used for hedges or screening as they will tolerate heavy pruning (spring or fall). Hemlocks in general are not recommended for use in extremely urban settings because of heat, salt and pollution sensitivity.

Site Requirements:

The Western hemlock prefers acidic, cool, moist to wet soils with good drainage. While the best growth may be obtained in full sun, like other hemlocks, the Western hemlocks are quite tolerant of partial to full shade. If planted in full sun, note that hemlocks may be stressed by extremely high temperatures or dry conditions. Avoid planting in sites with high summer heat. The Western hemlocks are also susceptible to high wind damage, salt damage, and air pollution. T. heterophylla is fully hardy in zones 5-7. In zones 3-4, hardiness is marginal and quite dependent on the geographic and altitudinal location of the seed source. To avoid excessive winter damage, look for plants grown from seeds obtained from high altitude regions in Montana or Idaho and plant in sites protected from the harshest winter exposure.

Sustainable Features:

Western hemlocks are resistant to hemlock woolly adelgid, an insect which ravages Canadian and Carolina hemlocks. Easily detected by the white, cottony egg masses, hemlock woolly adelgid infestations usually kill Canadian or Carolina hemlocks within three to five years of infestation.

Related Species:

Canadian hemlock (Tsuga canadensis) is the species native to the eastern U.S. and is most widely available. Carolina hemlock (Tsuga carolina), native of the southern Appalachian Mountains from Virgina to Georgia, is also widely planted and available in the northeast. Unfortunately, both of these species are highly susceptible to the hemlock woolly adelgid. Two other species, Mountain hemlock (Tsuga mertensia) and Japanese hemlock (Tsuga diversifolia) also are resistant to the hemlock woolly adelgid. However, their growth forms and textures are quite different from the Canadian or Western hemlocks. Also, their availability is limited and their hardiness is uncertain in the Northeast.

Where to See Them/Availability:

URI's Learning Landscape, Kingston, Rhode Island features specimens of the Western, Mountain and Japanese hemlocks. are Several varieties of hemlocks also are grown at the Arnold Arboretum in Boston, Massachusetts. Western hemlocks, grown from a cold-hardy (high altitude in Montana) seed source, are available from Western Maine Nurseries in Maine. Local nurseries intermittently carry Western hemlocks. Remember to ask about the seed sources for the trees. Those grown from coastal seed sources will be less cold hardy than trees from high altitude seed sources. The University of Rhode Island is currently working in partnership with Western Maine Nurseries and local Rhode Island nurseries to increase the availability of cold-hardy Western hemlocks.

Propagation Information for Growers:

Propagation of Western hemlock with cuttings is difficult and appears highly dependent on timing. Cuttings have been rooted successfully at the Arnold Arboretum. Cultivars such as the weeping forms are usually grafted. For seeds, cold stratification will decrease time to germination and increase strength of seedlings but may not always be an absolute requirement. Stratify at 40 degrees for 2-4 months in moist sand.