Eastern hemlock
Tsuga canadensis
also called canadian hemlock, hemlock
The most graceful conifer of the eastern forest, feathery and soft with a drooping leader, and the rare evergreen genuinely content in shade. Takes shearing well enough to make the finest hedge there is.
- Type
- Tree · Perennial
- Botanical family
- Mixed / other
- Foliage color
- Green
- Sunlight
- Part shade to full sun in the North
- Watering
- Moderate; shallow-rooted and quick to suffer in drought
- Soil
- Cool, moist, acidic, well-drained; never hot and dry
- Feeding
- Gentle all-organic
- USDA zones
- 3a–7b
- Frost tolerant
- Yes
- Plant out
- 14 days before the last spring frost
- Plant spacing
- 26 ft 3 in
- In-row spacing
- 19 ft 8 in
- Between rows
- 32 ft 10 in
- Square-foot density
- Not suited to SFG
- Root system
- A fine surface mat, and nothing below it
- Working depth
- 8–18 in
- Spread
- 30–44 ft across, about 1–1.5× the width of the plant
- Shallowest pot
- 16 in of soil
Hair-fine roots in a shallow felt, with no deep anchor to fall back on. It cannot chase water, so it is the first casualty of a drought and the first thing killed by a hoe. Mulch it, never cultivate around it, and never let it go dry in its first two summers.
A shallow plate of fine roots and no anchor, so a hemlock in the open blows over and a hemlock in a dry summer suffers before anything around it. It wants shade at the root, permanent mulch and never a spade.
Figures recorded for Eastern hemlock itself. Roots follow the soil either way: a compacted pan, a high water table or heavy clay stops them well short of any of it, and deep open ground lets them go further.
- Cats and dogs
- Confirmed safe
We say a plant is safe only where a named poison-control reference names that exact species and records it as non-toxic to both cats and dogs. Most plants are on nobody’s list, and their absence here is not a judgement about them. This is a record of what those references say, not veterinary advice, and it cannot account for your own animal, the quantity eaten, or a plant treated with anything.
The ASPCA files this under the common name Canada Hemlock, printing our exact species, Tsuga canadensis, and records it non-toxic to dogs, cats and horses. It also carries Hemlock Tree and Weeping Sargent Hemlock at genus level, and Carolina Hemlock as a different species. The Pet Poison Helpline Hemlock page prints no Latin name and sits alongside separate Poison Hemlock and Water Hemlock entries, so it cannot be matched to this plant: the poison hemlock of the toxic lists is Conium maculatum, an unrelated plant.
- When
- Not harvested, beyond a few fresh needle tips for tea. Shear hedges in late spring after the soft new growth extends.
- What to look for
- For a hedge, the pale new tips going deep green; for the tree, nothing to wait for.
- How to harvest
- Hedges: shear the new growth lightly, keeping the base wider than the top. Specimens: remove deadwood only. Check the underside of shoots each winter for the white wool of adelgid while you work.
- How often
- One shear a year for a hedge; a winter adelgid inspection for everything.
- Storing the crop
- Fresh green needles, steeped, make a citrusy tea rich in vitamin C. Dry, they are not worth keeping.
- Adelgids & woolly aphids Hemlock woolly adelgid, white wool at the needle bases; the existential threat through most of its range
- Scale insects Scale insects on needles and twigs
- Spider mites Spider mites bronzing the needles in a hot dry summer
- Drought stress Drought stress: the roots are shallow, and a dry August shows in the crown
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Ladybird (lady beetle) Coccinellidae
The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working.
- Green lacewing Chrysoperla carnea
Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing.
- Big-eyed bug Geocoris spp.Hunts Spider mites
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Hoverfly SyrphidaeHunts Scale insects
Bee-mimicking flies whose legless larvae graze aphid colonies clean while the adults pollinate. A ribbon of shallow, nectar-rich flowers kept in bloom all season recruits wave after wave of them.
- Minute pirate bug Orius spp.Hunts Spider mites
A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby.
- Predatory mites Phytoseiulus & AmblyseiusHunts Spider mites
Fast orange mites that hunt spider mites egg-by-egg, and cousins that clear thrips and fungus-gnat larvae. Sold as a biological control for greenhouses; outdoors they follow humidity — mist and mulch, don’t dust with sulfur.
- Rove beetle StaphylinidaeHunts Spider mites
Slim, quick beetles with short wing cases that hunt in soil and litter, taking root-fly eggs and larvae, fungus-gnat larvae, and mites. Mulch and undisturbed ground keep them resident year-round.
Not the poison hemlock of Socrates, which is an unrelated weed. This one makes tea. Check for white woolly adelgid at the needle bases before you buy, and know your region: where the adelgid is established, hemlock needs a treatment plan.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com