How to Grow and Care for Canadian Hemlock Trees

Along with its better-known relative, the eastern white pine, Canadian or eastern hemlocks are among the most common, native evergreen trees growing in the forests of eastern North America. They grow up to 70 feet tall and appear pyramidal or conical.

Their tiny, fragrant two-toned green needles give them a fine texture. Their needles are linear but form a spiral. Crushing the needles releases their aroma. They make small oval-shaped seed-containing cones just under an inch long, hanging from twig tips.

Plant Canadian hemlock in the early spring. These trees grow slowly or moderately, averaging about 12 to 24 inches annually. Canadian hemlock trees are a good, stately tree that is shade-tolerant and makes very little mess. It keeps its graceful look throughout the seasons. The key to successful Canadian hemlock care is to provide acidic soil with ample moisture; it can't handle drought well.

Interesting Facts About Canadian Hemlock

• The bark of Canadian hemlock trees at maturity is reddish-brown, one of the primary tree sources of tannins traditionally used for tanning hides for clothing during the 19th and early 20th centuries.
• Canadian hemlock wood is a softwood commonly used for making boxes, pallets, plywood, and framing for construction.
  
• Canadian hemlock is unrelated to poison hemlock (Conium maculatum), a flowering herbaceous plant. Canadian hemlock is not toxic to humans and pets.
  

Canadian Hemlock Care

This native tree is an indigenous species to the United States and, therefore, not invasive. Moderately slow-growing (12 to 24 inches per year) and long-lived (up to 800 years), Canadian hemlock trees in the wild can reach 70 feet tall or higher with a spread of 25 to 35 feet. However, you can keep Canadian hemlocks small by pruning them regularly every year.

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 the wind.

Plant the trees 30 to 40 feet apart. These shallow-rooted trees need protection from the wind, or you might return home one day after a storm only to find your tree lying on the ground.

Sun Requirements

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).

Soil Needs

These trees require soil that is moist but has good drainage. They prefer a loamy, acidic soil.

Water Requirements

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.

Ideal 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.

Fertilizer Requirements

This tree needs a well-balanced fertilizer (10-10-10) about once a year. For the amount to use, follow product label instructions. Do not add fertilizer to your hemlock right after transplanting because it can burn the root system and lead to the tree's death. Wait a few months until the tree is established.

Types 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 unsuitable.

• '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).

Pruning

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 has 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, 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-hardwood branches for propagation in late summer.

1. 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).
2. To encourage successful rooting, dip the base of the cutting entirely in a rooting hormone powder used for woody shrubs and trees.
3. 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.
4. Place the pot in a partially shaded spot in a greenhouse or inside the house near a window for the winter.
5. Keep the soil moist but not soaking.
6. Water the soil when the surface is dry to the touch.
7. 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 (cold stratification) is necessary for seedlings to emerge in the spring.

1. 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.
2. Water the soil until it is thoroughly moist.
3. Scatter the hemlock seeds over the surface.
4. Cover the seeds with about 1/2 inch of soil and water until the soil is thoroughly moist. Leave the area alone until spring.
5. Thin the seedlings by gently pulling out the smaller and weaker ones, leaving the stronger seedlings to continue growing without being crowded out.
6. Water the seedlings whenever the soil's surface feels dry to the touch.

Potting and Repotting Canadian Hemlock

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.

Treatments for Common Pests & Plant 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.