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The State of Canadian Hemlock

Canadian Hemlock - Small

Canadian Hemlock (also called Eastern Hemlock or Tsuga canadensis) is often known for its beautiful, majestic size and shape, with the potential to live over 800 years and grow up to 70 feet tall

However, recently Canadian Hemlock has seen some tough times. What follows is an outline of the current state of Canadian Hemlock, with topics ranging from the Hemlock Woolly Adelgid ravaging native stands, regulations aimed at controlling the spread and the impact of the adelgid, climate extremes impacting propagation of the species, and a look towards the future.

Hemlock Woolly Adelgid (HWA)

Hemlock Woolly Adelgid is an invasive species within the United States that was originally native to Japan. According to the Michigan State University Extension, this species was first discovered in the U.S. around 1950 in Virginia. Ever since then, the species has slowly made its way up North and has now been identified in at least 20 states. Check out the map below provided by the USDA Forest Service to get an idea of just how much the Woolly Adelgid has spread across the country. 

Where Woolly Adelgid on Canadian Hemlock has spread across the country.

So, what is this invasive species exactly? Hemlock Woolly Adelgids are small, invasive insects that latch onto the needles of the trees and suck the nutrients from them, eventually killing the Hemlock. David Smitley of Michigan State University Extension explains that one of the easiest ways to identify a Woolly Adelgid is by “looking at the hemlock shoots for the white ‘wool’ the adelgid produces while feeding.” According to Michigan Invasive Species, “Infested hemlocks become less vigorous and may turn grayish-green. Left untreated, hemlock woolly adelgid can cause tree death in 4-10 years.”

Canadian Hemlock Woolly Adelgid Infestation
Photo by Robert L. Anderson, USDA Forest Service, Bugwood.org.

Often, these invasive insects can be easily moved from tree to tree. Michigan Invasive Species identifies the following common ways in which it can travel:

  • Transportation by birds or other wildlife
  • Transportation by wind
  • Transportation by human gear, equipment, clothing, or vehicles
  • Transportation by infested nursery stock

There are a few treatments that can be used if a Canadian Hemlock is infected with Woolly Adelgids, however, the tree normally needs to be disposed of immediately to reduce the spread of the insect. 


To learn more, take a look at this video produced by Michigan State University Extension.

Canadian Hemlock Quarantines

Hemlock Woolly Adelgid has become such a serious issue that the USDA often requires certain Quarantine Compliance Agreements between nurseries, farms, and growers to ship Canadian Hemlock in order to try to control the spread. 

In the county that Vans Pines Nursery resides in (Ottawa County, Michigan) and the surrounding counties, we have an internal quarantine in effect. This quarantine requires that no plant material can move in or out of these regions without a certificate of compliance. This internal quarantine is in addition to the external quarantine in effect, which prohibits the movement of the plant material into Michigan from prohibited regions, which many other states have enacted for their imports.

Fortunately, Vans Pines works closely with the Michigan Department of Agriculture and Rural Development (MDARD) to ensure we are fully compliant in our management of HWA. On an annual basis, our Canadian Hemlock is preventatively treated and inspected by a local MDARD official. Only once our product is inspected are we issued a Certificate of Compliance, allowing us to ship our plant material both within our local internal quarantine zones and to any state with such a quarantine in place. 

Canadian Hemlock Seed Availability

A third, less discussed issue impacting the conservation and propagation of Canadian Hemlock is the effect of the inconsistent, extreme weather conditions on cone production. Bitter cold winters and late season frosts can have a devastating impact on the trees’ ability to produce a  viable cone crop, and that is exactly what we have seen reflected in seed availability this past few years.

For our production this year, we were only able to source about a quarter of the seed required to hit our sowing targets. This forces us to make a decision, experience a shortage in Spring of 2022 for plug availability due to reserving our limited production for internal container use, or experience a shortage in 2023 of containers by making these plugs available for sale Spring of 2022. We have opted for the former, and believe that to be a consistent choice for most nurseries. Expect to see young liner shortages across the industry in Spring of 2022. 

What does the future hold?

Considering the seed availability issue, it begs the question: What is the future of Canadian Hemlock if seed crops continue to be unviable? Fortunately, Canadian Hemlock is a species that can be propagated via cuttings, albeit with dramatically more inefficiency. Vans Pines is currently evaluating the potential of adopting a Hemlock cutting propagation program, particularly with the release of the USDA traveler variety, which claims a resistance to HWA.

With over 170 million Canadian Hemlock trees in Michigan forests alone, this isn’t a selection that will fade into obscurity in the face of this adversity. Conditions need to continue to be carefully monitored in order to preserve the life and quality of Canadian Hemlocks, and we will not be surprised when official initiatives are enacted to further assist in the conservation of this majestic species.  

To continue learning more about Canadian Hemlocks, check out the following resources below.