of Rhode Island GreenShare Factsheets
Landscapes: Western Hemlock
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.
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
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.
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
Western hemlocks are resistant to hemlock
woolly adelgid, an insect which ravages Canadian and Carolina
detected by the white, cottony egg masses, hemlock
woolly adelgid infestations usually kill Canadian or Carolina
hemlocks within three to five years of infestation.
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.
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
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.
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program