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Canadian Hemlock
Tsuga canadensis
Description & Overview
Gracefully pyramidal in youth, Canadian Hemlock becomes pendulously pyramidal and open with age. Light yellow-green spring growth changes to a lustrous dark green, with small, graceful cones held on the branches. Cooler, moister sites are best for this tree.
May also be known as Eastern Hemlock or Hemlock Spruce.
Core Characteristics
Suggested Uses:
This is one of few evergreens that will grow reliably in heavy shade. It is an ideal screening plant as long as the site requirements are met. It also functions well as a specimen tree. It should be planted in somewhat protected sites to protect it from wind burn and is excellent planted beneath established trees.
Wildlife Value:
Canadian Hemlock stands are an important habitat and food source for deer during the winter months and also provide cover to grouse and turkey. The dense canopy provides excellent cover for many birds and is preferred by Chickadees, Red Crossbills, White-winged Crossbills, Pine Siskin, and Rose-breasted Grosbeaks as a winter food source.
Canadian Hemlock provides nesting habitat for migratory birds when they travel north for spring including the Black-throated Blue Warbler, Black-throated Green Warbler, Blackburnian Warbler, and Magnolia Warbler. Ruffed Grouse, owls, and Wild Turkeys will roost on the branches of this evergreen tree.
Canadian Hemlock is a host plant to several moth species including the Columbia Silkmoth (Hyalophora columbia), False Hemlock Looper Moth (Nepytia canosaria), Hemlock Looper Moth (Lambdina fiscellaria), Hemlock Angle (Macaria fissinotata), Coleotechnites atrupictella, Powder Moth (Eufidonia notataria), Pine Measuringworm Moth (Hypagyrtis piniata), Gray Spruce Looper (Caripeta divisata), Small Pine Looper Moth (Eupithecia palpata), Black Zigzag (Panthea acronyctoides), Comstock’s Sallow (Feralia comstocki), and Spruce Budworm Moth (Choristoneura fumiferana).
Other feeders of Hemlock include the Black Vine Weevil (Otiorhynchus sulcatus), sawflies, scales, long-horned beetles, and wood-boring beetles.
Deer, snowshoe hares, beavers, porcupines will both browse on twigs, foliage, and wood. Mice, moles, voles, squirrels will feed on seeds and small seedlings.
Maintenance Tips:
As it requires good moisture, Canadian Hemlock should be watered during dry periods. Maintaining a good mulch ring will do wonders for the tree, keeping the soil cool for the roots to establish. Water well going into winter.
The dense habit of Canadian Hemlock does not require shearing. If pruning is necessary, do so during the winter months.
Avoid excessive fertilization. Mulching and moisture are more important for good growth.
Pests/Problems:
Hemlock Wooly Adelgig (HWA) is the primary insect threat. This insect is thankfully not present in Wisconsin but has caused severe losses in the Appalachian Mountains. In a landscape setting, this insect can be prevented by using an Imidacloprid pesticide.
Cytospora Canker and Needle Rust may be of concern in stressed trees. These are best avoided by keeping the tree healthy.
Drought is a serious concern for Canadian Hemlock, which does not tolerate extended periods of dryness. Make sure that the plant is well-watered going into winter to prevent wind burn.
Deer will frequently eat the foliage of Canadian Hemlock. Use a repellent spray like Bobbex to keep the deer at bay. Heavy browsing can kill a young tree if more than a third of the canopy is eaten.
Leaf Lore:
Canadian Hemlock is one of our climax forest species in Wisconsin Forests. It’s commonly found with American Beech and Yellow Birch in acidic, well drained soils. If you’ve ever strolled through the woods and seen a very dark patch, it was likely beneath the shade of Canadian Hemlocks. Few plants can grow in this heavy shade, but you can often find sedges, clubmoss, and Canadian Hemlock seedlings growing beneath.
The furrowed, rich brown-red bark and persistent cones are excellent ornamental characteristics. If you have a need for a shade tolerant evergreen, this is a top choice.
Canadian Hemlock has the greatest shade tolerance of all North American trees. It can survive with as little as 5% sunlight! In environments like this, it grows extremely slow. A 3″ DBH (diameter at 4.5 feet off ground) tree may be 200 years old! They are also long-lived, with some specimens reported to be over 900 years old.
In areas with higher light levels, Canadian Hemlock will grow much faster.
In the wild, Canadian Hemlock relies on coarse woody debris to grow. These are large pieces of trees that have fallen and decayed over decades. Seedlings have an easier time of germinating on these trunks due to their high moisture and nutrient content.
Companion Plants:
The heavy shade cast by this evergreen makes it difficult for many perennials or shrubs to grow beneath. Consider using Canada Wild Ginger or False Solomon’s Seal around the dripline, which will spread as the tree grows larger and act as a living mulch for the soil.
