Tree · Pinaceae
Eastern Hemlock
Tsuga canadensis
Set in cool, moist shade, eastern hemlock fills out with soft, flat, feathery needles into an 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 of the cool forests of eastern North America, where the old trees stand for centuries. Its short, flat needles are dark green above with pale silvery undersides, set in flat sprays along the twigs, and they carry only small brown cones. Branch by branch the foliage layers into a soft, feathery, pyramidal shape, the leader and outer twigs nodding at the tips, a far gentler outline than the rigid spires of pines and spruces.
What the tree wants most is cool, moist shade. It is one of the most shade-tolerant conifers there is, holding its dense green sprays under taller trees where many evergreens thin to bare, scrawny branches. The cost of that softness is a low tolerance for stress, since heat, drought, drying wind, road salt, and city air all turn the fine needles brittle and brown, so a sheltered north-facing or woodland site suits it far better than an open, sunny lawn.
One real threat shows up first on the foliage itself. The hemlock woolly adelgid, a tiny invasive insect, leaves white woolly specks where the needles meet the twigs and has stripped huge stretches of wild hemlock across the eastern states, and a garden tree is not immune. Grown in the right spot and checked over for those telltale white flecks, though, a hemlock asks for little and gives back a deep, layered curtain of green that holds all year.
Care
The short version: cool partial shade, steady moisture, and rich acidic soil that never dries out, plus a yearly close look at the needles and twigs for the white flecks of woolly adelgid.
Light
Hemlock holds its dense, flat needle sprays in partial to full shade and is one of the few conifers that stays full under taller trees. It tolerates some sun, but an open, hot site bleaches the deep green and thins the foliage to bare twigs, so a cool, sheltered spot keeps it looking lush.
Water
The soil stays consistently moist and never bakes dry, because this tree has no tolerance for drought and a long dry spell crisps the fine needles brown and can kill it outright. Deep watering in dry weather and a cool blanket of mulch over the roots hold that moisture in.
Soil
Plant it in cool, moist, acidic, well-drained ground, whether loam, sand, or clay. A pH of 5.0 to 6.0 suits it best. Soil that dries out around the roots, or sits soggy and warm, is the one thing it will not forgive.
Temperature
Eastern hemlock is cold-hardy down to -40°F (-40°C), the needles holding through hard winters, and copes with summer heat up to about 95°F (35°C). It is the dry, exposed heat that scorches the foliage rather than the temperature alone, so cool air and shade matter more than the thermometer.
Humidity
Ordinary outdoor humidity is fine, and there is no number to chase. The tree prefers a cool, moist setting over a hot, drying one that desiccates the slender needles, and a sheltered woodland edge keeps the air around the foliage gentle.
Feeding
A light early-spring feeding with a balanced or acidifying tree fertilizer is plenty. Hemlock grows slowly and puts on only short flushes of soft new needles, so a single seasonal application suits it, and heavy feeding does more harm than good.
Pruning
Hemlock takes shearing better than most conifers, its dense twiggy growth knitting into a smooth green face, which makes it a fine hedge or screen. Formal hedges are trimmed in late spring to early summer. Left as a specimen it needs almost no pruning and looks best in its natural feathery, drooping-tipped form.
Repotting
This is a landscape tree rather than a container plant, so it is rarely repotted. A dwarf form kept in a pot moves up only when roots circle the inside, the soft new 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 its tiered branches 25 to 35 feet (7.5 to 10.5 m) wide, so a specimen needs 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. Young trees go out in spring or early fall while the soil is cool and damp and their fine roots can take hold, and seed sown straight from the small brown cones needs a long winter chill first, since 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 reads right in the needles, whether as pale flecking, bronzing, and white woolly specks from pests on the undersides, or as browning tips where a site runs too hot and dry. Caught early, the woolly adelgid can be stopped and the tree saved. Match the look of the foliage below, then act before the canopy thins to bare twigs.
White woolly beads along the twigs and needles fading to gray-green
Rows of tiny white woolly beads, like specks of cotton stuck where each needle meets the twig, are the work of the hemlock woolly adelgid, an invasive sap-sucker that has stripped wild hemlock across the eastern states and kills an untreated tree over a few years. As it feeds, the needles drain to a dull gray-green and drop, and branches die back from the tips. A registered systemic insecticide applied as a soil drench or injection from late September into October stops it, and a certified arborist is the move for a large, high-value tree.
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
Slim brown-to-yellow scales clamped to yellowing needle undersides
Flip a yellowing branch and the undersides of the needles are studded with narrow, elongated covers shading from brown to yellowish, the waxy armor of elongate hemlock scale pressed flat against the green. As the insects feed, the needles pale, thin, and fall. Horticultural oil or a systemic insecticide timed to the active young crawlers clears it, a heavily encrusted branch is pruned away, and a well-watered tree holds its color through a light infestation 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
Bronzed, pinprick-stippled needles veiled in fine webbing
Needles flecked with countless pale pinpricks, fading from green to a tired bronze and draped in fine silk webbing, are the calling card of spider mites, which surge in hot, dry weather. Tap a branch over a sheet of white paper and the dust resolves into tiny crawling specks. A hard jet of water knocks them loose, horticultural oil or a miticide follows for a heavy case, and steadier watering with a little afternoon shade keeps the foliage green and the mites gone.
Fix:
- Spray foliage with water to dislodge mites
- Apply horticultural oil or miticide if severe
- Improve watering and provide afternoon shade
Crisp brown needles and a see-through canopy on an open site
Needles crisping to brown at the tips, a canopy gone thin enough to see through, and bare twigs on a sunny, windy, or salt-splashed spot are drought and scorch, not a pest, because hemlock cannot take hot, dry, exposed conditions. The fine foliage dries out faster than the roots can replace the water. Deep soaking through dry weather, a cool blanket of mulch over the roots, and shelter from afternoon sun, drying wind, and road salt bring it back, and the lasting answer is 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
For households with pets and children, the soft-needled eastern hemlock conifer is not poisonous. The ASPCA lists it as non-toxic to cats, dogs, and horses, and not a needle or cone on the tree is harmful to chew or handle. Do not confuse it with poison hemlock, an unrelated lacy-leaved weed covered in the myths below.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe for cats. The ASPCA lists this conifer as non-toxic, so a cat that bats at and bites a soft needle tip comes to no harm.
Dogs None
Safe for dogs. Chewing the flat needles or mouthing a small brown cone does no harm, though a big swallowed mouthful might bring a passing stomach upset, as with any plant.
Horses Safe
No toxicity here. A horse can browse the low, soft-needled branches of an eastern hemlock with no risk of poisoning.
Rabbits Safe
Harmless to rabbits. The short flat needles carry nothing poisonous, so a wild or pet rabbit nibbling the lowest sprays is fine.
Livestock Safe
Cattle, goats, and sheep can graze around the tree safely, since not a needle or cone on it holds a toxin.
Birds Safe
Birds are in no danger. Many species tuck into the dense, feathery branches to shelter and feed, and the small seeds are a natural food source.
People Safe
No part of the tree is poisonous to people. This is the harmless conifer with the soft flat needles, 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, some cascading, some flattened, some dished like a green nest, 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 spill downward in cascading green curtains that pool on the ground, ending far wider than tall.
'Jeddeloh'
A slow-growing dwarf shrub whose branches dip toward a hollow, dished, nest-shaped center, a compact green bowl that fits small gardens and foundation beds.
'Cole's Prostrate'
A ground-hugging dwarf that presses flat over rocks and slopes, its bare older stems showing as it creeps outward rather than climbing up.
How to propagate
Eastern hemlock can be raised from the tiny seeds in its small brown cones or from cuttings, but neither is quick, and the named garden forms are nearly always struck from cuttings to keep their distinctive shapes.
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
The tiny seeds shake loose from small brown cones as the scales begin to part, and raising them tests your patience. Each seed needs about 100 days of moist chilling through winter before sowing in late winter to spring, since it will not break dormancy without that cold rest. Germination creeps along for months and the small, soft-needled seedlings take years to establish, yet they push on in 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 what hold the named dwarf and weeping forms true to their distinctive shapes, since seed will not reproduce them. Firm, semi-hardwood shoots are taken from late fall into winter and dipped in rooting hormone to coax new roots from the cut base. Even then rooting is slow and erratic, often dragging on for several months, so this suits a patient grower.
Myths
The hemlock tree is the deadly poison hemlock that killed Socrates, so it is dangerous to grow.
This tall, soft-needled evergreen conifer in the pine family is harmless, 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 with lacy leaves and white flower clusters, and water hemlock is a third toxic plant from that same family. The towering tree and those low poisonous herbs look nothing alike and share only a name, by pure coincidence.