Canadian or eastern hemlock trees are members of the Pinaceae (pine) family. If you have heard of poison hemlock, particularly the hemlock tea that ancient Greek philosopher Socrates was forced to drink, Canadian or eastern hemlock is not the same plant; no part of this tree is poisonous. Conium maculatum and Circuta maculata are the poisonous hemlocks. The bark of the Canadian hemlock is one of the primary tree sources of tannins traditionally used for tanning hides for clothing during the 19th and early 20th centuries.
Along with its better-known relative, the eastern white pine, these trees are among the most common evergreen trees growing in the forests of eastern North America. They are pyramidal or conical in shape and their small, fragrant two-toned green needles give them a fine texture. The bark of Canadian hemlock trees at maturity can be reddish-brown.
Canadian hemlock trees are shade tolerant and make very little mess, keeping their graceful look throughout the seasons. Plant them in the spring or summer 30 to 40 feet apart and they will grow 12 to 24 inches per year.
|Botanical Name||Tsuga canadensis|
|Common Name||Eastern or Canadian hemlock|
|Plant Type||Evergreen conifer|
|Mature Size||70 ft. tall with a spread of 25 to 35 ft.|
|Sun Exposure||Full to partial shade; tolerates full sun in cold northern climates|
|Soil Type||Rich and moist|
|USDA Hardiness Zones||3 to 7 (USDA)|
|Native Area||Eastern North America|
Canadian Hemlock Care
Moderately slow-growing and long-living, Canadian hemlock trees in the wild can reach 70 feet tall or higher with a spread of 25 to 35 feet. These are fragrant plants and crushing the needles releases their aroma. The tree produces small (up to 3/4 inch long), tan-colored, pendant-shaped seed-bearing cones that ripen in the fall and release seed during the winter. It is best grown in cool, moist, well-drained soils and protected from wind, if possible.
Unlike many large trees, Canadian hemlocks grow best in full to part shade and will tolerate full sun in cold northern climates. Their sunlight requirements provide quite a bit of flexibility if you live in a cold climate (USDA Zones 3 to 5).
These trees require soil that is moist but has good drainage. They prefer a loamy, acidic soil. Shallow-rooted, these trees need protection from the wind, or else you might return home one day after a storm only to find your tree lying on the ground.
Hemlock trees require a fair amount of water. They can tolerate less favorable conditions (partial sun in average soils of alkaline pH) if sufficient supplemental water is given during the dry periods of summer, but the soil must be well-drained. This tree does not tolerate standing wet soil nor prolonged periods of drought.
The best method of watering is slow watering once a week. Start the watering process with a general spray of the trunk and leaves. This will help to wash away insects and pollution residues. Then, place the garden hose at the base of the tree and allow it to run for 15 to 20 minutes—this will distribute the water to the root system effectively.
Temperature and Humidity
This tree grows in regions with cool, humid climates. In the northern areas, January temperatures average 10 degrees Fahrenheit and July temperatures average 60 degrees Fahrenheit. Precipitation ranges from less than 30 inches.
This tree needs a well-balanced fertilizer (10-10-10) about once a year. Do not add fertilizer to your hemlock during transplanting because it can burn the root system and it could lead to the death of the tree. Wait a few months until the tree is established.
Varieties of Canadian Hemlock
Many cultivars of Canadian hemlock have been developed for landscape use, they have been bred for circumstances where a taller tree is not suitable.
- 'Gentsch White': This dwarf shrub-like cultivar has white or cream variegated foliage and a round, globe-like shape. It matures at only five 5 in height (by about the same width).
- 'Aurea Compacta' (also known as 'Everitt's Golden'): This bright golden-colored cultivar has an upright habit and reaches 5 feet in height, with a spread of only about half that.
- 'Sargentii' or 'Pendula': Also known as weeping Canadian hemlocks, these two cultivars are large shrub forms with an attractive weeping or arching habit. They reach about 12 feet tall or more (and can be twice as wide).
Canadian hemlock trees do not need much pruning unless limbs are damaged by weather or disease. Prune in spring and early summer because the tree is in active growth and will easily recover. Avoid pruning hemlock trees in fall or winter because the tree will become confused, returning to active growth instead of going dormant to withstand the winter.
Compact cultivars, which are essentially shrubs, are commonly used as privacy hedge plants or in foundation plantings. If you begin pruning them when young, they are fairly easy to shape.
Propagating Canadian Hemlock
Canadian hemlock cuttings can be taken from semi-ripe branches for propagation in late summer.
- Cut the new part of a branch that grew in the current season. The branch should be green at the tip but browning toward the base of the node. Make a clean cut (no tearing or breaking the branch).
- To encourage successful rooting, dip the base of the cutting entirely in a rooting hormone powder used for woody shrubs and trees.
- Place the cutting in a pot filled with well-drained potting mix. Push the base of the cutting into the soil about 2 inches deep.
- Place the pot in a partially shaded spot in a greenhouse or inside the house near a window for the winter.
- Keep the soil moist but not soaking.
- Water the soil when the surface is dry to the touch.
- Transplant the cutting in the late spring to a planting bed suitable for sowing hemlock seeds.
How to Grow Canadian Hemlock From Seed
Sow hemlock seeds in the fall so they can spend the winter outdoors. The chill of the long cold winter period is necessary for sprouts to emerge in the spring. If you sow hemlock seeds in the spring or summer, they will not germinate.
- Choose a sowing site that receives partial shade and is not too crowded by other trees.
- Prepare a planting bed there with well-drained, fertile soil—mix sand, compost, and manure together with the topsoil.
- Water the soil until it is thoroughly moist.
- Scatter the hemlock seeds over the surface.
- Cover the seeds with about 1/2 inch of soil and water until the soil is thoroughly moist.
- Leave the area alone until spring.
- Thin out the seedlings by gently pulling out the smaller and weaker ones, leaving the stronger seedlings to continue growing without being crowded out.
- Water the seedlings whenever the surface of the soil feels dry to the touch.
Common Pests & Diseases
Canadian hemlocks have two major drawbacks in the form of pests that attack them: the wooly adelgid insect and white-tailed deer.
Hemlock woolly adelgid (Adelges tsugae) is an invasive, tiny sap-sucking insect (a relative of the aphid) that has become a threat to the hemlocks in their native areas of eastern North America and home landscapes. Treatment with pesticides is available but controlling an infestation is extremely difficult.
Canadian Hemlocks can also be damaged by deer; perhaps seek an alternative tree or shrub with better deer resistance if your area has a heavy deer population that frequently damages your trees and shrubs.
O. Canham, Hugh. Hemlock and Hide: The Tanbark Industry in Old New York. Northern Woodlands, 2011.