Tree · Pinaceae
Eastern Hemlock
Tsuga canadensis
Plant it in cool, moist shade and the eastern hemlock grows into a soft, feathery evergreen that lasts for generations.
Partial shade
Every 3–7 days
USDA 3–7
40–70 ft · 12.2–21.3 m
Overview
Eastern hemlock is a slow-growing evergreen conifer native to the cool forests of eastern North America, where old trees can stand for centuries. It carries short, flat needles and small brown cones, and the whole tree takes on a soft, feathery, pyramidal shape that sets it apart from stiffer pines and spruces. Left alone it climbs to forest height, but it also takes shearing well, which is why so many gardeners grow it as a hedge.
What this tree wants more than anything is cool, moist shade. It is one of the most shade-tolerant conifers there is, happy under taller trees where many evergreens would thin and sulk. The trade-off is a low tolerance for stress: heat, drought, drying wind, road salt, and city air all wear it down, so a sheltered north-facing or woodland site suits it far better than an open, sunny lawn.
There is one real threat to keep in mind. The hemlock woolly adelgid, a tiny invasive insect, has killed huge stretches of wild hemlock across the eastern states, and a garden tree is not immune. Grown in the right spot and checked for pests, though, a hemlock asks for little and gives back a dense, year-round screen of green.
Care
The short version: cool partial shade, steady moisture, and rich acidic soil that never dries out, plus a yearly look for woolly adelgid on the needles.
Light
Hemlock thrives in partial to full shade and is one of the few conifers that grows well under taller trees. It tolerates some sun, but an open, hot site bleaches and thins the foliage, so lean toward a cool, sheltered spot.
Water
Keep the soil consistently moist and never let it bake dry. This tree has no tolerance for drought, and a long dry spell can kill it outright, so water deeply in dry weather and mulch to hold the moisture in.
Soil
Plant in cool, moist, acidic, well-drained ground, whether that runs to loam, sand, or clay. A pH of 5.0 to 6.0 suits it best. The one thing it will not forgive is soil that dries out or sits soggy and warm.
Temperature
Eastern hemlock is cold-hardy down to -40°F (-40°C) and copes with summer heat up to about 95°F (35°C). It is the dry, exposed heat rather than the temperature alone that does the damage, so cool air and shade matter more than the thermometer.
Humidity
Ordinary outdoor humidity is fine, so there is no number to chase. The tree simply prefers a cool, moist setting over a hot, drying one, and a sheltered woodland edge keeps the air around it gentle.
Feeding
Feed lightly in early spring with a balanced or acidifying tree fertilizer. Hemlock is a slow grower with modest needs, so a single seasonal application is plenty and heavy feeding does more harm than good.
Pruning
Hemlock takes shearing better than most conifers, which is what makes it such a good hedge or screen. Trim formal hedges in late spring to early summer. Left as a specimen it needs almost no pruning and looks best in its natural feathery form.
Repotting
This is a landscape tree rather than a container plant, so it is rarely repotted. If you do grow a dwarf form in a pot, move it up only when roots circle the inside, growth stalls, or water runs straight through the soil.
Size & spacing
A mature forest tree reaches 40 to 70 feet (12 to 21 m) tall and spreads 25 to 35 feet (7.5 to 10.5 m) wide, so give a specimen plenty of room. Dwarf cultivars stay far smaller and fit beds and rockeries.
When to plant
Hemlock is hardy through zones 3 to 7 and is planted, not sown on a quick schedule. Set young trees out in spring or early fall while the soil is cool and damp, and if you start from seed, give it a long winter chill first because germination is slow.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Sow stratified seed in late winter; seed needs about 100 days of moist chilling before sowing
- Plant: spring or early fall
- Harvest: Non-flowering conifer; tiny brown cones about 2 cm long mature in autumn
Hardiness
USDA hardiness zones: 3–7
Temperature: down to -40°C
Troubleshooting
Most hemlock trouble shows up in the needles, either as pests on the undersides or as browning brought on by a site that runs too hot and dry. Catch the woolly adelgid early and you can save the tree. Match what you see below, then act before the canopy thins.
White woolly tufts on the twigs and a slowly thinning tree
Those cottony white masses at the base of the needles are the hemlock woolly adelgid, an invasive sap-sucker that has wiped out wild hemlock across the eastern states and can kill an untreated tree over a few years. A registered systemic insecticide, applied as a soil drench or injection from late September into October, is the way to stop it. For a large, high-value tree, bring in a certified arborist.
Fix:
- Apply a registered systemic insecticide (soil drench/injection or basal bark) per label, most effectively late September through October
- Treat high-value landscape trees preventively and re-treat on the label interval
- Consult a certified arborist for large trees needing soil injection
Yellowing needles with narrow scales stuck underneath
Turn a yellowing branch over and look for the narrow, waxy covers of elongate hemlock scale clinging to the needle undersides. Treat with horticultural oil or a systemic insecticide timed to when the young crawlers are active, and prune out any branch that is heavily crusted. A vigorous, well-watered tree shrugs off light infestations far better than a stressed one.
Fix:
- Apply horticultural oil or a registered systemic insecticide timed to crawler emergence
- Prune out and destroy heavily infested branches
Stippled, bronzing needles with fine webbing in hot weather
When needles take on a dull, stippled bronze cast and you spot faint webbing, spider mites are usually the cause, and they flare up in hot, dry spells. Tap a branch over white paper to see the tiny mites move, then blast the foliage with water and follow up with horticultural oil or a miticide if it is bad. Better watering and a little afternoon shade keep them from coming back.
Fix:
- Spray foliage with water to dislodge mites
- Apply horticultural oil or miticide if severe
- Improve watering and provide afternoon shade
Browning, scorched needles on a hot, exposed site
Browning needles and a thinning canopy on a sunny, windy, or salt-splashed spot point to drought and scorch rather than any pest. Hemlock simply cannot take hot, dry, exposed conditions. Water deeply through dry weather, mulch to keep the roots cool, and shelter the tree from afternoon sun, drying wind, and road salt. The lasting fix is to plant it in a cool, moist, shaded site from the start.
Fix:
- Water deeply and regularly during dry periods
- Apply mulch to keep roots cool and moist
- Provide shelter from wind, afternoon sun, and road salt
Toxicity
Good news for households with pets and children: the eastern hemlock conifer is not poisonous. The ASPCA lists it as non-toxic to cats, dogs, and horses, and no part of the tree is harmful to chew or handle. Do not confuse it with poison hemlock, an unrelated weed covered in the myths below.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe. The ASPCA lists this conifer as non-toxic to cats, so a curious nibble on the needles is nothing to worry about.
Dogs None
Safe. A dog can chew the foliage or a fallen cone without harm, though as with any plant a big mouthful might cause a passing stomach upset.
Horses Safe
No toxicity here. Horses can browse near an eastern hemlock without any risk of poisoning.
Rabbits Safe
Harmless to rabbits. The needles hold nothing poisonous, so a wild or pet rabbit nibbling the lower branches is fine.
Livestock Safe
Cattle, goats, and sheep can graze around the tree safely, since no part of it carries a toxin.
Birds Safe
Birds are in no danger. Many species shelter and feed in hemlocks, and the seeds are a natural food source.
People Safe
No part of the tree is poisonous to people. This is the harmless conifer, not the deadly poison hemlock herb it shares a name with.
No special handling precautions for toxicity; foliage is harmless.
Varieties
Beyond the towering forest tree, breeders have selected dwarf and weeping forms that fit a small garden or rockery. These are the ones you are most likely to find at a nursery.
'Pendula' (Sargent's weeping hemlock)
A low, mounding weeper whose branches cascade to the ground, growing far wider than it ever does tall.
'Jeddeloh'
A dwarf, slow-growing shrub with a dished, nest-shaped center that suits small gardens and foundation beds.
'Cole's Prostrate'
A ground-hugging prostrate dwarf that spreads flat across rocks and slopes rather than rising up.
How to propagate
You can raise eastern hemlock from seed or from cuttings, but neither is quick, and the named garden forms are nearly always grown from cuttings to stay true.
SeedModerate
Collect seed from cones just beginning to open; sow after stratification in late winter to spring · Slow; several months to germinate and years to establish
Growing hemlock from seed asks for patience. Give the seed about 100 days of moist chilling through winter before you sow it in late winter to spring, since it will not sprout without that cold rest. Germination takes months and the seedlings need years to establish, but they handle deep shade better than almost any other young conifer.
Stem cuttingsDemanding
Late fall to winter using semi-hardwood cuttings · Several months to root; rooting can be slow and erratic
Cuttings are how the named dwarf and weeping forms are kept true to type, since seed will not reproduce them. Take semi-hardwood cuttings from late fall into winter and treat them with rooting hormone to lift your odds. Even then rooting runs slow and erratic, often taking several months, so this is a method for the patient grower.
Myths
The hemlock tree is the deadly poison hemlock that killed Socrates, so it is dangerous to grow.
The eastern hemlock tree is a harmless evergreen conifer in the pine family, and no part of it is poisonous. The poison that killed Socrates came from poison hemlock, an unrelated weed in the carrot and parsley family, and water hemlock is a third toxic plant from that same family. The tree and the poisonous herbs share only a name, by pure coincidence.