Common Name: Canadian hemlock
Type: Needled evergreen
Family: Pinaceae
Zone: 4 to 7
Height: 6.00 to 8.00 feet
Spread: 3.00 to 4.00 feet
Bloom Time: Non-flowering
Bloom Description: Non-flowering
Sun: Part shade to full shade
Water: Medium
Maintenance: Low
Leaf: Evergreen
Other: Winter Interest
Tolerate: Deer, Heavy Shade, Black Walnut
Culture
Easily grown in average, medium moisture, well-drained soils in part shade to full shade. Best sited in part shade in sheltered locations protected from strong drying winds and hot afternoon sun. Tolerates full sun in cool northern climates, but dislikes the hot and humid summers of the deep South (particularly south of USDA Zone 6) where sun scald may damage the foliage when temperatures consistently exceed 95 degrees F. Intolerant of drought and should be watered regularly in prolonged dry spells, particularly when plants are young. Appreciates a thick winter mulch.
Noteworthy Characteristics
Tsuga canadensis, commonly called Canadian hemlock or eastern hemlock, is a dense, pyramidal conifer of the pine family that is native to moist woods, moist slopes, rocky hillsides/ridges, wooded ravines, and stream valleys from eastern Canada south to Maine and Wisconsin and further south in the Appalachian Mountains to Georgia and Alabama. It grows to 40-75’ tall in the wild. This species is noted for having the smallest needles and cones in the genus. Flat sprays of lacy evergreen foliage give this tree a graceful form. Short dark green needles (to 9/16" long) with two white bands beneath are arranged in two opposite rows. Needles are attached to twigs by slender stalks. Small, pendant, short-stalked, seed-bearing cones (to 3/4" long) are tan-brown. Lower branches often dip toward the ground. Thick and ridged bark on mature trees is red-brown to gray-brown. State tree of Pennsylvania. No part of this tree is poisonous. The poisonous hemlocks (Circuta maculata and Conium maculatum) are herbaceous perennials in the parsley family.
Genus name of Tsuga is derived from the Japanese name for trees in this genus.
Specific epithet means native in part to Canada.
‘Slenderella’ is a narrow pyramidal small tree or large shrub that grows to 6-8’ tall over the first 10 years. It may eventually fully mature to 12’ tall. It has a columnar form with slender upright branches clad with short evergreen dark green needles.
Problems
A healthy plant in the proper environment has few problems. Potential disease problems for plants in the genus Tusga include needle blight (needles turn yellow and die), canker, rusts and rots. Potential insect problems include bagworms, borers, leaf miner, saw fly and spider mites. Foliage may scorch in very hot weather. Prolonged drought can be fatal.
Hemlock woolly adelgid (HWA) is a tiny (1/32”) sap-sucking insect (relative of the aphid) that has recently become a serious threat to the survival of native hemlocks in the wild in the eastern United States. HWA was accidentally introduced into the U. S. in the 1920s from Eastern Asia. It has been known to exist in the Pacific Northwest since 1927, but was first observed in the forests of Virginia in the 1950s. It has now spread from Virginia into the southern and middle Appalachians. Inability to survive cold winters has so far substantially limited HWA’s northern spread to as far as Massachusetts, but northward expansion into much of New England is expected as winter temperatures continue to moderate. HWA has killed most of the old growth hemlocks in the Great Smoky Mountains National Park and 95% of the hemlocks in Shenandoah National Park. HWA was discovered in Pennsylvania’s Allegheny National Park in November of 2013. Treatment of HWA is available (pesticides containing imidacloprid or dinotefuran), but control of this pest is very difficult.
Uses
Small evergreen conifer for shady areas of the landscape. Specimen or in small groups. Screen/hedge.