Eastern Hemlock (Tsuga canadensis)

An evergreen tree from the Pine Family (Pinaceae)

Eastern Hemlock, also known as Canadian Hemlock, is a popular landscape tree found in urban areas throughout the state of Ohio. However, as a native tree, it is only found in the eastern half of Ohio, primarily in Appalachia. Eastern Hemlock is native to southern Canada, the northeastern United States, and all of the Appalachian Mountains down to Georgia. In the wild, it thrives on the north slopes of hills and mountains or tucked into ravines, where there is more shade, cooler conditions, and more moisture in the acidic, organic, well-drained soils of slopes.

Size varies tremendously based upon local growing conditions, but in general Eastern Hemlock slowly reaches 70 feet in height by 35 feet in spread at favorable sites. Specimens can achieve twice that size under optimum conditions, while small trees planted in unfavorable urban sites struggle to survive, let alone grow into mature trees. Its growth habit is upright pyramidal and often remaining branched and foliaged to the ground under sunny conditions. A distinctive trait of Eastern Hemlock is the drooping nature of its terminal leader and the terminals of all side branches, especially during the new shoot growth of spring.

Planting Requirements - Eastern Hemlock achieves its best growth in evenly moist, acidic, organic, rich, well-drained soils in partial shade to partial sun. It can tolerate less favorable conditions (such as full sun in average soils of alkaline pH) if sufficient supplemental water is given during the dry periods of summer, as long as the soil is well-drained. Eastern Hemlock does not tolerate wet soils, nor prolonged drought. Strongly windswept areas and air polluted sites should be avoided. It generally performs best in partial sun to partial shade, and is found in zones 3 to 7.

Potential Problems- In addition to the planting conditions noted above, Eastern Hemlock suffers from one major pest, the woolly adelgid. This pest has wreaked havoc in areas of Canada and the northeastern United States where Hemlock is a climax forest tree, as well as being planted as an ornamental. Control of this pest is difficult. In addition, root rot plagues Hemlock when it is sited in poorly drained (waterlogged) soils, ironically causing the tree to appear as if it needs water. In most of these cases, the tree is already in decline and soon dies.

It takes especially well to shearing as a young formal tree, and can be utilized as a formal hedge, especially in shady urban areas. As a member of the Pine Family, it is related to other Hemlocks, as well as the Firs, Larches, Spruces, and Pines.

Leaf Identification Features

Eastern Hemlock, like Balsam Fir, has two rows of short, flattened, dark green needles on each side of its thin twigs. However, the needles of Eastern Hemlock are much smaller, and occur on extremely short petioles (being "stalked needles").

The needles have blue-white undersides, caused by stomatal bands (microscopic pores) that appear to merge as solid lines. Eastern Hemlock is the most finely textured of evergreens, with its soft miniature foliage and abundance of thin, pendulous twigs.

Other Identification Features

When grown at commercial nurseries, Eastern Hemlock is repeatedly sheared to achieve a "full look" while still young. Upon transplanting and without further shearing, numerous branches emerge from the young tree, and continue to give it a full, yet natural look. Trees found in nature are often more open in their growth habit when young, especially in shaded sites.

Eastern Hemlock is monoecious, having separate male (catkin) and female (cone) flowers in mid-spring. The female flowers quickly develop into small green cones that hang from the tips of the new growth of twigs.

After the cones mature and open to release their seeds, they may remain on the branches for several years.

Eastern Hemlock has bark that starts out as fairly smooth on young branches, becomes very flaky on young trunks, and then transitions to prominent fissures and wide, flattened ridges with maturity, having a brown to brown-gray coloration. Even in old age, some Eastern Hemlocks continue to have branches and foliage to the ground, hiding their trunks and bark.