Tree · Pinaceae
Eastern Hemlock
Tsuga canadensis
Set in cool, moist shade, eastern hemlock becomes a soft, feathery evergreen that gives a garden a quiet, lasting presence.
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 from the cool forests of eastern North America, the kind of tree that settles into a landscape for generations rather than seasons. Its short, flat needles and small brown cones give it a soft, feathery, pyramidal shape that reads far gentler in a garden than the rigid lines of pines and spruces. Left to its own height it becomes a stately backdrop, yet it also takes shearing beautifully, which is why it has long served as a living wall.
Above all, this is a plant for cool, moist shade, and that makes it the rare conifer for the difficult shaded corner where little else will thrive. It is one of the most shade-tolerant conifers there is, content beneath taller trees where other evergreens grow leggy and dull. The trade is that it dislikes stress, so heat, drought, drying wind, road salt, and city air all wear on it, which makes a sheltered, north-facing, or woodland setting the natural home for it rather than an open, sunny lawn.
There is one consideration worth folding into the plan. The hemlock woolly adelgid, a tiny invasive insect, has erased great sweeps of wild hemlock across the eastern states, and a garden specimen needs the same watchfulness. Placed thoughtfully and looked over now and then, though, a hemlock asks little and rewards a space with a deep, year-round screen of green that frames everything around it.
Care
The short version: give it a cool, partly shaded corner, soil that stays evenly moist, rich, and acidic and never dries out, and a yearly look over the needles for woolly adelgid.
Light
Hemlock is happiest in partial to full shade and is one of the few conifers that furnishes a shaded corner with real character. It will accept some sun, but an open, hot position bleaches and thins the foliage and dulls its look, so a cool, sheltered spot keeps it at its best.
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 be the end of it, so water deeply through dry weather and lay down mulch to hold the moisture and keep the planting looking lush.
Soil
Set it in cool, moist, acidic, well-drained ground, whether the bed leans to loam, sand, or clay. A pH of 5.0 to 6.0 suits it best. The one condition it will not abide is soil that dries out or sits soggy and warm, so good drainage in a cool spot is the foundation.
Temperature
Eastern hemlock is cold-hardy to -40°F (-40°C) and copes with summer heat to about 95°F (35°C). It is the dry, exposed heat rather than the temperature alone that troubles it, so a cool, shaded placement does more for its appearance than any reading on the thermometer.
Humidity
Ordinary outdoor humidity is all it asks, so there is no figure to chase. The tree simply favors a cool, moist setting over a hot, drying one, and a sheltered woodland edge keeps the air around it soft and the foliage fresh.
Feeding
Feed lightly in early spring with a balanced or acidifying tree fertilizer, and leave it at that. Hemlock is a slow grower with modest needs, so a single seasonal feeding keeps it healthy, while heavy feeding does more harm than good.
Pruning
Hemlock takes shearing more gracefully than most conifers, which is what makes it such an elegant hedge or screen. Trim formal hedges in late spring to early summer. Left as a specimen it needs almost no pruning and looks loveliest in its own natural feathery form.
Repotting
This is a landscape tree rather than a container plant, so it is seldom repotted. Where a dwarf form lives in a pot on a shaded terrace, move it up only when roots circle the inside, growth slows, 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 a specimen needs a generous stage. Dwarf cultivars stay far smaller and slip neatly into beds, borders, and rockeries.
When to plant
Hemlock holds its own through zones 3 to 7, and it is a plant you settle in rather than rush from seed. Place young trees in spring or early fall while the soil stays cool and damp and roots can take hold, and if a seed-grown start appeals, allow it a long winter chill first, since it comes along slowly.
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 of a hemlock's troubles read in its needles, whether from pests working the undersides or from browning where a site runs too hot and dry. Spotting the woolly adelgid early is what keeps the tree, and the garden, intact. Match what you see below, then step in before the screen begins to thin.
White woolly tufts on the twigs and a quietly thinning screen
When a once-lush garden hemlock loses its fullness and you notice cottony white flecks at the base of the needles, the hemlock woolly adelgid is at work, an invasive sap-sucker that has hollowed out wild hemlock across the eastern states and can take an untreated tree within a few years. Protecting that green backdrop calls for a registered systemic insecticide, applied as a soil drench or injection from late September into October. For a mature tree that anchors the whole garden, a certified arborist is the graceful solution.
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 in the screen with slim scales hidden underneath
If the rich green of a hedge starts to fade to yellow, lift a branch and study the needle undersides for the slender waxy covers of elongate hemlock scale. A treatment of horticultural oil or a systemic insecticide, timed to the active young crawlers, brings it back, and any heavily crusted branch is best pruned away to keep the line clean. A tree kept well watered holds its color through a light infestation far better than one left to struggle.
Fix:
- Apply horticultural oil or a registered systemic insecticide timed to crawler emergence
- Prune out and destroy heavily infested branches
Bronze-cast, stippled needles with fine webbing through a hot spell
Foliage that turns dull and stippled with a bronze cast, threaded with faint webbing, usually signals spider mites, which arrive on the heels of a hot, dry spell. Hold white paper beneath a branch and tap to watch the tiny mites scatter. A firm rinse of water clears most of them, with horticultural oil or a miticide in reserve for a stubborn case. More water and a little afternoon shade keep the canopy looking fresh and the mites at bay.
Fix:
- Spray foliage with water to dislodge mites
- Apply horticultural oil or miticide if severe
- Improve watering and provide afternoon shade
Scorched, browning needles where the site runs hot and open
Browned needles and a thinning silhouette in a sunny, windy, or salt-splashed corner point to drought and scorch rather than any pest, a sign the site is simply too exposed for hemlock, which has no taste for hot, dry, open conditions. Deep watering through dry weather, a generous mulch to cool the roots, and shelter from afternoon sun, drying wind, and road salt all help it recover its poise. The lasting answer is to place it from the start in a cool, moist, shaded part of the garden where it can settle and stay handsome.
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 a home that includes pets and children, the news is reassuring: 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. Take care only not to confuse it with poison hemlock, an unrelated weed addressed in the myths below.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
A cat is welcome to wander the garden freely, since the ASPCA lists this conifer as non-toxic and a curious nibble on the needles asks for no concern.
Dogs None
A dog that chews the foliage or carries off a fallen cone comes to no harm, though, as with any plant in the garden, a large mouthful might bring a passing stomach upset.
Horses Safe
Horses can browse near an eastern hemlock in complete safety, with no risk of poisoning whatsoever.
Rabbits Safe
Rabbits face no danger here, since nothing in the needles is poisonous, so a wild or pet rabbit grazing the lower branches is perfectly fine.
Livestock Safe
Cattle, goats, and sheep can graze around the tree without concern, as not a single part of it carries a toxin.
Birds Safe
Birds are entirely safe, and a hemlock often becomes a small sanctuary where many species shelter and feed, with the seeds offering 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 with which it happens to share a name.
No special handling precautions for toxicity; foliage is harmless.
Varieties
Beyond the grand forest tree, breeders have selected dwarf and weeping forms scaled for a small garden or rockery, where they bring presence without bulk. These are the cultivars you are most likely to find offered at a good nursery.
'Pendula' (Sargent's weeping hemlock)
A low, mounding weeper whose branches pour to the ground, settling far wider than tall and giving a border a soft, sculptural anchor.
'Jeddeloh'
A slow-growing dwarf shrub with a gently dished, nest-shaped center, tailor-made for a small garden or a refined foundation planting.
'Cole's Prostrate'
A ground-hugging dwarf that flows flat across rocks and slopes instead of rising, lending a rock garden a quiet, layered look.
How to propagate
Eastern hemlock can be raised from seed or from cuttings, though neither is a quick affair, and the named garden forms are nearly always grown from cuttings so their distinctive shapes carry through.
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
Raising hemlock from seed is a slow, contemplative project for a gardener who enjoys the long view. The seed wants about 100 days of moist chilling through winter before sowing in late winter to spring, since it will not stir without that cold rest. Germination unfolds over months and the seedlings take years to establish, yet they handle deep shade better than almost any other young conifer, a quiet virtue in a layered garden.
Stem cuttingsDemanding
Late fall to winter using semi-hardwood cuttings · Several months to root; rooting can be slow and erratic
Cuttings are what keep the named dwarf and weeping forms true to their refined shapes, since seed will not reproduce them. Take semi-hardwood cuttings from late fall into winter and treat them with rooting hormone to better the odds. Even then the rooting is slow and erratic, often running several months, so this is a labor of love for the unhurried gardener.
Myths
The hemlock tree is the deadly poison hemlock that killed Socrates, so it is dangerous to grow.
The unease around the name is misplaced, because 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, while water hemlock is a third toxic plant from that same line. What the elegant garden tree and those toxic herbs share is nothing more than a name, and that by pure coincidence.