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Past Articles Library | Trees | Plant Profile: Eastern Hemlock (Tsuga canadensis)


The Eastern Hemlock is also known as the Canadian Hemlock and can be found in many landscaped yards.  The beauty of this evergreen tree comes from its Christmas tree looking shape and its distinctive   bark.  While the Eastern Hemlock’s natural shape is that of a perfect upright pyramid, the shape is enhanced through shearing while at the nursery and tree farm but once you get it home, the evergreen tree really has a chance to show its natural beauty.  As the cosmetic pruning stops, the plant will begin to fill in with numerous branches and in doing so will look fuller.

The bark really begins to show off once the plant goes from a young sapling to a mature tree.  The bark of a young tree starts out smooth.  Then, as the tree and branches age, the bark begins to have a flakey appearance that is then followed with the appearance of distinguishing fissures and wide ridges that are flat.  This older bark also has a brown to grey brown coloration, which looks striking in any landscape. 

The foliage of this plant is evergreen in nature and is dual colored.  The top surface of the needles is a dark green while the underside is a blue green.  The needles themselves are on double rowed and supported on thin stems by extremely short needle stalks or petioles.

Another feature of the Eastern Hemlock is its pinecone.  Compared to other pine type trees, the pinecone of the Eastern Hemlock is small but decorative.  The little pinecones themselves resemble little ornaments on the end of the branches of this evergreen tree. 

While this tree is very attractive, it does have some problems.  Two major ones are the Hemlock Woolly Adelgid, and root rot.  The later is caused by an invasive insect species that is destroying both native and nursery hemlocks alike.  The symptoms of this pest show up as little cotton sacs that look like the end of cotton swabs.  These little sacs will be located at the base of needles and protects both the pest and its eggs from the weather.  These sacs can be seen in early winter but are more likely viewed during the spring.  When the pests come out of their sacs, they begin to suck on the plant at its tips.  This sucking of the tree’s sap stunts growth and eventually kills the needles.  In 4 to 10 years, the tree will become defoliated and die.  At this time, the only course of action is to remove a tree with this disease.

Root rot, on the other hand, is more controllable.  Preventing this starts with the proper selection of a planting site.  Root rot is caused by planting the tree in an area that does not have well-drained soil.  In doing so, the excess moisture in the ground causes the root mass to rot.

Location, location, location is not only important for preventing root rot but also for the general well-being of the tree.  Too many hemlocks have been planted in the correct environmental condition but did not have enough space to grow properly.  In this case, many hemlocks have suffered from the demise of a bad pruning.  To avoid this, pick a location that is spacious and can handle a tree that can reach 70 feet in height with a spread of 35 feet.  While this tree has a medium growth rate, it is always a good idea to plan your plantings according to mature size of the plant and not the immediate size.


Besides having enough room, the tree will need to be in a soil that is moist but well-drained, and acidic along with having a high percentage of compost running throughout the soil.  Light requirements are somewhat narrow and can range from areas that receive partial shade to partial sun.

Also, avoid planting hemlocks in areas that receive strong winds constantly.  The winds alone can dislodge a hemlock.  Another concern about hemlocks is their sensitive to air pollination.  Avoid planting in areas with high levels of all types of air pollution.

Once you have selected the proper location and you have your tree, the next step is to dig a proper hole.  This hole will need to be four times the width of the root mass and only as deep as the container it came in.  After the hole has been dug, test out the hole before moving on to the next step.

If the hole is the correct size, the next step is to remove the tree from the container.  Do not pull the tree out of the pot.  Instead, cut away the container.  Doing this simple step will protect the plant from any damage.  If you have purchased a tree that is balled, remove any twine wrapped around the tree and slit the burlap.  There is no need to remove the burlap since it will rot away but if there is any material sticking up out of the ground when the tree is planted, always remove that.  Not removing this fabric will cause a “wicking” action and deplete your tree of moisture.  If the tree has a tight root system, gently loosen up some of the roots so that the root mass will grow outward.

After the tree has been placed in the ground, water in.  This will give the tree a chance to take up moisture, which in turn will reduce planting shock.  Then, backfill with a combination of compost mixed with the removed soil.  Water in again and add additional soil if needed.

Once the tree is planted, apply two to four inches of mulch.  This will both protect the truck of the tree from mowing and/or weeding eating equipment, and will also conserve soil moisture while reducing weeds.   

Continue to monitor soil moisture throughout the season until the tree becomes established, which can take several years. 

But what if you cannot find a tree?  Then, propagate one through seed and all you need for this process is hemlock pinecones.  Hemlocks are monoceious, which means there are separate male and female parts.  Male components are called catkins while females are referred to as cones.

In the mid spring, female flowers turn into little green cones at the end of the branches.  Once the cones are brown and begin to slightly open, the seeds are mature and ready to pick.

Pick the pinecones and place in a paper bag.  Store in a warm location and wait for pinecone to open.  Once open the seed will fall into the bag.  After that has happened, fill a container with moist sand or peat and place seeds inside this mixture.  Store in a refrigerator for one to four months, which is the stratification process for this plant.  If possible, leave the seeds in this cold environment as long as possible.  The longer the exposure to cold, the better the germination rate will be.

After the cold period has passed, plant your seeds in a partially sunny location after your local frost-free date.  Monitor soil moisture and water as needed.



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