Tsuga canadensis aka Eastern Hemlock

Eastern hemlock, Tsuga canadensis, is an evergreen conifer in the pine family. Gardeners also know it as Canadian hemlock or Canada hemlock. It grows wild in eastern North America, from Nova Scotia and Quebec west to Minnesota. Its range runs south through the Appalachian Mountains to northern Georgia and Alabama. In the wild it favours cool, moist slopes, ravines and stream valleys.

This is a medium to large tree with a dense, conical or pyramidal outline. Most sources give a height of 40 to 70 feet (12 to 21 m). Old trees can reach about 80 feet (25 m). The spread is usually 25 to 35 feet (8 to 11 m). The branches spread out level from the trunk and droop gracefully at the tips. Young trees look neat and full, but old trees often become ragged and irregular.

The needles are flat, glossy and dark green, mostly under 3/4 inch (2 cm) long. Each has two narrow white bands on its underside. They sit in two flat rows, giving the foliage a soft, lacy look. New spring growth is a lighter yellow-green. The slender twigs are hairy and grey-brown. Mature bark turns reddish-brown to grey-brown, with deep furrows and scaly ridges. As a conifer, the tree has no true flowers. Small yellow pollen cones cluster near the branch tips in spring. The seed cones are oval and brown, about 3/4 inch (2 cm) long. They hang from the twigs and ripen in autumn.

Eastern hemlock wants cool, moist, well-drained soil that is acidic or close to neutral. It grows in full sun or part shade and tolerates heavy shade better than most conifers. Shelter it from strong, drying winds. In hot southern summers it does best in part shade, since strong sun can scorch the foliage. It tolerates neither drought nor heat, so water it during dry spells, above all while young. A thick winter mulch helps. It is very cold-hardy, rated to USDA zone 3 and RHS H7. Growth is fairly fast.

Gardeners use it as a lawn specimen, a screen or a clipped hedge. It is one of the few needled evergreens that screens well in shade. It takes hard pruning in spring but looks best left alone. Dwarf and weeping cultivars suit small gardens better than the full-size tree. Birds and small mammals eat the seeds, and grouse feed on the buds. Dense branches give winter cover to deer and turkeys.

Hemlock woolly adelgid is the most serious pest. Left untreated, this tiny sap-sucking insect can kill a large tree in about three years. Other pests include scale insects, borers, spider mites, bagworms and sawflies. Diseases include needle blight, cankers, rusts and root rot. The tree dislikes air pollution and salt spray. Deer may browse the foliage or rub the bark. The ASPCA lists it as non-toxic to dogs, cats and horses. It is not the poisonous herb also called hemlock. People have eaten the inner bark in times of famine. The young shoot tips make a herbal tea.