Mountain Hemlock Plant Care

Mountain Hemlock (Tsuga mertensiana) belongs to the Pinaceae family within the Tsuga genus. Mountain Hemlock is native to the west coast of North America, found between Southcentral Alaska and south-central California. Mountain Hemlock is also known as Western Hemlock, Alaska Hemlock, Pacific Hemlock.

Mountain Hemlock displays a pyramidal, conical tree growth habit, reaching up to 60 ft tall with a spread of approximately 25 ft. Mountain Hemlock produces small, inconspicuous cones.

Leaf size: approximately 1.5 inches.

Water a young or newly planted Mountain Hemlock every 7–14 days, soaking the whole root zone, until it is established — usually one to two growing seasons. Established trees mainly need water during long dry spells. In a container, water whenever the top few centimetres of soil are dry.

Mountain Hemlock thrives in full sun to partial shade.

Tsuga mertensiana tolerates temperatures of 0–80°F. Mountain Hemlock prefers humidity levels of 40–70%.

Well-draining, acidic soil with high organic content. Good drainage is essential for Mountain Hemlock to prevent waterlogging, which leads to root rot and fungal issues.

Choose a spot with full sun to partial shade and well-draining, acidic soil with high organic content. Avoid low spots where water collects after rain.

Mountain Hemlock is suited to USDA Zone 5a – 8b.

Plant container-grown or balled-and-burlapped trees in spring or early autumn, setting the root flare at soil level, and water well after planting.

Mountain Hemlock can spread to about 25 ft (7.6 m) and reach about 60 ft (18 m) tall. Space plants about 25 ft (7.6 m) apart so mature crowns don't crowd each other, and plant at least half that distance from buildings, fences and paths.

Planning a row or hedge? Try the tree spacing calculator.

Mountain Hemlock needs little pruning. Remove dead, damaged or crossing branches in late winter or early spring.

Don't cut back into old, bare wood: conifers in the pine family rarely sprout new growth from it. To keep a denser shape, trim only the soft new shoots in late spring.

Mountain Hemlock is hardy down to USDA zone 5a, so once established it can stay outdoors through winter in that zone and warmer ones.

Water deeply in late autumn before the ground freezes — evergreens keep losing water through their needles all winter, and spread a 5–8 cm (2–3 in) layer of mulch over the root zone, keeping it away from the trunk.

Young and container-grown trees need extra protection: roots in a pot freeze much more easily than roots in the ground.

Mountain Hemlock can be propagated through seeds, cuttings. Similar propagation techniques also apply to chinese hemlock plant care, which shares the same genus.

See all plants toxic to cats and plants toxic to dogs.

Mountain Hemlock is susceptible to aphids, spider mites, scale insects. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.

Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.

Mountain Hemlock grows outdoors in USDA Zone 5a – 8b. It survives winters down to planting zone 5a. Mountain Hemlock is native to the west coast of North America, found between Southcentral Alaska and south-central California.