Mountain Hemlock, Tsuga mertensiana
I thought it would be good to have a look at a true Northwest native, the mountain hemlock. This is an alpine tree with an impressive range in the western United States: it grows at higher elevations from the coastal range in Alaska down through the entire Cascade Mountain range and into the central Sierra Nevada Mountains of California. To the east, this tree can be found throughout the Rocky Mountains in British Columbia, western Montana and Idaho.
Mountain hemlock is a slow growing conifer that, in spite of its preference for mountainous growing conditions, still performs relatively well in the landscape at lower elevations. Regardless of where it grows, this tree keeps an excellent, narrow crown shape that is characteristic of many alpine conifer species. It can reach heights of 100’ or more in the wild but most specimens in the landscape are much shorter—around 50 feet—which make this tree desirable in urban planting locations where other native conifers might quickly outgrow the space.
Needles of the mountain hemlock are shorter than other native conifers and vary in length, approximately 3/4” and shorter. Foliage is also packed tightly on the stem, grey-green in color and ‘rosemary-like’ in appearance. Cones are small, usually about an inch and a half in length yet they provide interest all year long as they develop and mature.
The mountain hemlock is relatively pest free. It is a host for the wooly adelgid like other hemlock species, but wooly adelgid is generally not considered a serious problem in Washington state. This pest seems to prefer feeding on western hemlock (Tsuga heterophylla) over the mountain hemlock.
In the old days, the only way this tree found its way into the nursery trade was from ‘collected’ stock, that is, specimens that were harvested (in many cases, poached) from the wild. Today this tree is grown as an ornamental and several named cultivars are available in the trade such as ‘Elizabeth’ and ‘Glacier Peak’.
Mountain hemlock is relatively drought tolerant once established and the tree can live for many years in a large container. This tree is very hardy on both sides of the state but it will struggle in the hot afternoon sun east of the Cascades. In these hottest portions of eastern Washington, select the mountain hemlock for locations with a cooler microclimate such as the north sides of buildings.
This tree’s relatively slow growth and slender habit make it a good choice for a landscape that needs a smaller, well behaved native conifer. Mountain hemlock shed some needles year round like any conifer but this is only a minor inconvenience for a tree with so much else to offer.
By Robert Buzzo
Robert Buzzo has worked in the nursery industry in Western Washington for over 40 years. For the past 28 years he has been the Manager of Lawyer Nursery, Inc. in Olympia. He has a degree in Plant Science from UC Davis, is a Certified Professional Horticulturalist (CPH) and is a member of the Washington State Nursery & Landscape Association (WSNLA).