Called the aristocrats of evergreens, hemlock trees (Tsuga spp.) are striking, graceful, even poetic. They add texture and color to any yard and a touch of class with their artistically spaced, slightly drooping branches. Four species of this exceptional tree are native to the U.S. and, as the elite of landscape conifers, definitely merit consideration.
Eastern hemlock (Tsuga canadensis) is in no hurry. It spends two decades reaching its full height of 40 feet, but will live up to 1,000 years. It provides habitat and nurture for deer, rabbits, birds, small mammals and porcupines. The elegant tree loves cool, moist slopes, well-draining soil and partial shade in U.S. Department of Agriculture plant hardiness zones 3 through 7. Weeping cultivars include Sargent's weeping hemlock (Tsuga canadensis "Pendula"), which grows to 15 feet tall and twice as wide, its weeping branchlets cascading over straighter branches in USDA zones 4 through 8. This tree is attacked by an aphidlike insect pest called the hemlock wooly adelgid, introduced from Asia, and the insect has devastated forests in the eastern U.S.
Only the largest backyards can accommodate the Western hemlock (Tsuga heterophylla), a true giant. It grows into an enormous and glorious tree, sometimes shooting up more than 250 feet tall with a spread of 40 feet in USDA zones 6 through 8. It stands erect, with blue-green flattened needles on its downward-sloping branches. Although it does not live as long as Eastern hemlock, the tree has a 150-year life span.
Mountain hemlock (Tsuga mertensiana) grows in USDA zones 6 through 8, and, like Western hemlock, frequently grows more than 100 feet tall. This species is narrow for its height, columnar in form, and for that reason is highly valued by those looking for a pyramidal conifer with tight foliage. The needles of the mountain hemlock are flat, no longer than 3/4 inch long, and spiral around the branches. Given a position in partial shade and enough water, these trees grow 1 foot or more a year and live more than 150 years.
It's an airy tree, the Carolina hemlock (Tsuga caroliniana), its short branches dainty and pendulous despite the narrow canopy. Look for this tree growing wild across the Appalachian Mountains on dry slopes at elevations from 2,500 to 4,200 feet. Carolina hemlock can shoot up to 100 feet tall in the wild, but generally stays less than 60 feet tall and 25 feet wide in yards in USDA zones 6 through 7. Its mahogany-hued bark develops attractive fissures as the tree matures.