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Eastern Hemlock

Posted: April 27, 2013

On June 22, 1931, the Pennsylvania Legislature adopted the eastern hemlock as our state tree.
Photos Courtesy of James Lashomb and Jianxin Zhang

Photos Courtesy of James Lashomb and Jianxin Zhang

  • "Whereas, The hemlock (Tsuga Canadensis Linnaeus) is still today, as it was of old, the tree most typical of the forests of Pennsylvania; and
  • Whereas, The hemlock yielded to our pioneers the wood from which they wrought their cabin homes; and Whereas, The hemlock gave its bark to found a mighty industry;  and
  • Whereas, The hemlock everywhere lends kindly shelter and sure haven to the wild things of forests; and
  • Whereas, The lighted hemlock at Christmas time dazzles the bright eyes of the child with an unguessed hope, and bears to the aged, in its leaves of evergreen, a sign and symbol of faith in immortality."
The eastern hemlock (Tsuga canadensis), is not exclusive to our state, and it is also called Canada hemlock or hemlock spruce:
  • It is a slow growing tree, and lives quite well in shady areas, unlike other trees.
  • It can take 200 - 300 years for a hemlock to reach its maturity.
  • The record height is 175 feet tall and seventy-six inches in diameter.
  • This hemlock was used in the past in construction, and the tannin found in the bark was used to die leather goods.

Today, the eastern hemlock is primarily a landscape tree. However, its main industrial use for wood pulp, especially for newsprint. So thanks to the eastern hemlock, you can have your Sunday paper.

Just before the eastern hemlock was adopted as a state tree, the hemlock woolly adelgid, HWA, was introduced accidently in this country in the late 1920’s. Some thirty years later the HWA was seen in the East. It is a serious threat to our state symbol. Not being a native insect, it has few predators to keep the population in check. This insect can kill a tree in as little as four years.

The easiest way to tell if your eastern hemlock has HWA is to look at the branches:

  • If you notice small white clumps, it may be HWA. Other symptoms include the needles that turn greyish green then drop off, and limb die back from the bottom up.
  • Once the tree is weakened from HWA, it is vulnerable to other pests and diseases.

To help reduce the spread of HWA:

  • do not place bird feeders in hemlocks as they will use the bird to hitchhike to other eastern hemlocks.
  • If you have an infected tree, do not fertilize it. Research has shown nitrogen fertilizers enhance the insect and doubles its reproductive rate.

The homeowner can attempt to manage the pest. The newly hatched nymphs are unprotected and exposed. Once the HWA is under those white cottony-masses, it is difficult to treat. So with timed applications of insecticidal soap or horticultural oil, the eastern hemlock can be treated. A licensed commercial applicator can use stronger pesticides to manage the insect. It is important to remember that treatment is lifelong for the tree. Continued applications must be applied.

For more information on the hemlock woolly adelgid, contact the Penn State Master Gardeners in Lackawanna County at 570-963-6842 or email: LackawannaMG@psu.edu. We have a free factsheet on this insect.

Steve Ward, Master Gardener Coordinator, Penn State Extension, Lackawanna County