Eastern hemlock (Tsuga canadensis) really takes its time to mature. In fact, it may take up to 300 years to reach what’s considered adulthood among evergreen trees. It can even live for another 100 years if conditions are right. Other names for this majestic species include hemlock spruce and Canada hemlock.
| Common name | Canada hemlock, Canadian Hemlock, Eastern Hemlock, Hemlock Spruce, Spruce Pine |
| Botanical name | Tsuga canadensis |
| Family | Pinaceae |
| Species | canadensis |
| Origin | North Central and Eastern U.S.A., Eastern Canada |
| Life cycle | Woody |
| Plant type | Native Plant |
| Hardiness zone | 3, 4, 5, 6, 7 |
| Sunlight | Dappled Sunlight |
| Maintenance | Low |
| Soil condition | Clay |
| Soil ph | Acid |
| Drainage | Well-Drained |
| Growth rate | Fast |
| Spacing | 24 – 60 ft. |
| Harvest time | Fall |
| Height | 4- 70 ft. |
| Width | 4- 70 ft. |
| Leaf color | Brown, Copper |
| Fruit color | Brown, Copper |
| Stem color | Brown, Copper |
| Garden style | Children’s Garden |
| Uses | Lawn |
I. Appearance and Characteristics
Tsuga canadensis, also known as eastern hemlock, eastern hemlock-spruce, or Canadian hemlock, and in the French-speaking regions of Canada as pruche du Canada, is a coniferous tree native to eastern North America. It is the state tree of Pennsylvania. Eastern hemlocks are widespread throughout much of the Great Lakes region, the Appalachian Mountains, the Northeastern United States, and Maritime Canada. They have been introduced in the United Kingdom and mainland Europe, where they are used as ornamental trees.
The eastern hemlock grows well in shade and is very long lived, with the oldest recorded specimen, found in Tionesta, Pennsylvania, being at least 554 years old. The tree generally reaches heights of about 31 m (102 ft), but exceptional trees have been recorded up to 53 m (174 ft). The diameter of the trunk at breast height is often 1.5 m (4 ft 11 in), but again, outstanding trees have been recorded up to 1.75 m (5 ft 9 in). The trunk is usually straight and monopodial, but very rarely is forked. The crown is broadly conic, while the brownish bark is scaly and deeply fissured, especially with age. The twigs are a yellow-brown in color with darker red-brown pulvini, and are densely pubescent. The buds are ovoid in shape and are very small, measuring only 1.5 to 2.5 mm (0 to 1⁄8 in) in length. These are usually not resinous, but may be slightly so.
The leaves are typically 15 to 20 mm (0.59 to 0.79 in) in length, but may be as short as 5 mm (0.20 in) or as long as 25 mm (1 in). They are flattened and are typically distinct, or two-ranked. The bottom of the leaf is glaucous with two broad and clearly visible stomatal bands, while the top is a shiny green to yellow-green in color. The leaf margins are very slightly toothed, especially near the apex. The seed cones are ovoid in shape and typically measure 1.5 to 2.5 cm (5⁄8 to 1 in) in length and 1.0 to 1.5 cm (3⁄8 to 5⁄8 in) in width. The scales are ovate to cuneate in shape and measure 8 to 12 mm (3⁄8 to 1⁄2 in) in length by 7.0 to 10 mm (1⁄4 to 3⁄8 in) in width. The apex is more or less rounded and is often projected outward. Twenty-four diploid chromosomes are present within the trees’ DNA.
II. How to Grow and Care
Sunlight
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 flexibility in a cold climate (USDA zones 3 to 5).
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.
Watering
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.
Soil
Eastern Hemlock has relatively high soil requirements. It must be nutrient-rich, fresh to moist and permeable. The evergreen tree also reacts sensitively to highly calciferous soils. Therefore, the intended terrain should have an acidic to neutral pH value.
Fertilizing
Eastern hemlock trees do best with a thorough yearly application of fertilizer in the fall. The recommended type of fertilizer is a balanced, slow-release granular or rich compost, as well as an application of magnesium treatment, depending on the quality of your soil. Only give fertilizer to well-established trees, as newly planted ones are prone to being burnt and even killed by fertilizer.
Pruning
The Eastern Hemlock is known to tolerate pruning. The best time to reach for the shears is in spring, before budding, so from February to April. If you would like to achieve better branching, you should only prune wood during the first year. Older trees are reluctant to bud. This applies in particular to branches which are over three years old.
If you would like larger trees to have narrower growth, you can readily trim the side branches or remove one of two trunks at the base, provided the tree has several trunks. It is also possible to cap the top. However, you should be prepared for the tree to then offshoot several tips, which does not make the Tsuga canadensis look more attractive.
Hedges can also be cut a second time, on a cloudy day during the summer. Take care to ensure that the cut is made in a pyramid shape.
Propagation
Canadian hemlock cuttings can be taken from semi-hardwood 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 of 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 a 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 from Seed
Sow hemlock seeds in the fall so they can spend the winter outdoors. The chill of the long cold winter period (cold stratification) is necessary for seedlings to emerge in the spring.
- Choose a sowing site that receives partial shade and is not too crowded by other trees. Prepare a planting bed with well-drained, fertile soil—mix sand, compost, and manure 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 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 soil’s surface feels dry to the touch.
Potting and Repotting
Canadian hemlock is a tall and wide tree meant to be planted in the landscape. Even dwarf varieties are not suitable for growing in containers, except when grown as a bonsai.
Overwintering
As a tree that is native to North America and whose northern habitat range runs along the southern border of Canada, it is a cold-hardy tree that does not require any winter protection.
Pests and Diseases
Canadian hemlocks have two major enemies: 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. Infested trees have white woolly masses at the base of the needles on the undersides of the twigs. Treatment with pesticides is available, but controlling an infestation is extremely difficult.
Canadian Hemlocks can also be damaged or destroyed by browsing deer. If you have a heavy deer population, choose an alternative tree or shrub with better deer resistance instead.
III. Uses and Benefits
- Ornamental uses
Eastern hemlock makes a good lawn tree for shady gardens. Small, lacey needles on slender twigs give the tree an elegant form. It can handle aggressive pruning, so it is suitable for topiary and for very formal, structured gardens. When carefully maintained, it can be grown into a hedge. It is best combined with shade perennials like lily-of-the-valley and Dutchman’s breeches.
- Culinary uses
American pioneers made tea from the tree’s leafy twigs and used its branches as brooms. Tea can be made from needles. The inner bark, which is best in winter and coming into spring, can be eaten raw or boiled; it can also be used to make flour.
- Other uses
The wood is soft, coarse-grained, and light buff in color. Air-dried, a cubic foot (0.028 m3) weighs 28 pounds (13 kg). The lumber is used for general construction and crates. Because of its unusual power of holding spikes, it is also used for railroad ties. Untreated, the wood is not durable if exposed to the elements. As a fuel, it is low in value. The wood is also a source of pulp for paper manufacturing.