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The Monday Garden
Great Americans: Hemlocks (Tsuga)

Issue No. 150 - February 6, 2005
by Sue Sweeney

Hemlocks, the trees, are members of the pine family, and had nothing to do with poisoning Socrates-- that villain was an herbaceous plant related to parsnips. Instead, our native hemlocks are rare in that there are few big trees that can be accurately described as “cute”, “dainty”, “airy”, “graceful”, “feathery”, “delicate”, and “fine”. The cones are especially adorable and, fortunately, come in large numbers and stay on the tree most of the year.
picture: hemlock (Tsuga) cones in winter, Morgan Street at 3rd Street, Stamford CT January 2005
In North America we’re blessed with three native hemlocks – the cool-loving eastern hemlock, Tsuga canadensis, the more southern Tsuga caroliniana, and the gigantic western Tsuga heterophylla.
These hemlocks are forest trees. Particularly the eastern and southern versions like the dappled shade, wind protection, and summer cool and moisture of the forest environment. These slow growing trees can take 30 years or more to get mature enough to produce seeds but are said to live an astonishing 800 to 1,000 years. The eastern version is a medium to tall tree (up to 70 or 100 feet); the southern is a bit smaller – may be 60’. The western Tsuga heterophylla can stretch an incredible 200 feet into the air. Now, that’s tall.

In the forest, all three hemlocks spread into massive stands that provide a snug winter home for everyone from warblers and flying squirrels to moose calves and bear cubs. The veggie eaters enjoy the seeds and like to munch on the new growth and inner bark.

From a distance, you can tell hemlocks by the straight trunks and pyramid shape. The shape is like a spruce, only more open and airy with feathery-looking straight, horizontal branches that droop at the ends, and rough gray-brown or cinnamon-brown bark.

Close up the “giveaways” are the petite, flat needles arranged in messy rows of two. The needles look slightly irregular as though handmade by a child. The eastern hemlock has tiny teeth on leaf margins; the southern doesn’t. The southern hemlock’s needles are a bit larger and more leathery or plastic-y looking than the eastern’s. All have white stripes on the needle underside. The color is dark olive to dark green is summer, light lime when new, and often yellowish in winter.


pictures: tiny, aqua-green baby hemlock cones May 2004, get longer and greener in June 2004,
Morgan Street at Hoyt Street , Stamford CT

In their proper environment, hemlocks are wonderful; the eastern one even hedge prunes fairly well. However, they don’t do that well out of the forest, particular the young ones who expect to grow up in the protective shade of their parents. In the yard, young hemlocks need to be treated like an understory tree such as the flowering dogwood. Plant in part shade (morning sun is great) and protect from winter winds; keep well watered in droughts but never let stand in water; and, whatever you do, keep them away from road salt, car exhausts, and the neighbor’s dog. I have seen small hemlocks in patio pots survive drought, sun and wind year after year but the result is pleasing only if you like the half-dead old tree bonsai look.

pictures: typical hemlock branch structure, bark, and overall form, Morgan Street at Hoyt Street, Stamford CT 2004

Outside of their proper environment, hemlocks get all kinds of pests and diseases, and die, often young. So, wonderful as they are, don’t plant one unless you’ve got the right place. Walking around town, I often see baby hemlocks dying in full sun or standing water, or with their road-side branches killed by salt. The problem with poor culture is that you not only loose your bought-and-paid-for plant but you can foster diseases that then go on to threaten the neighbors and our remaining forests.

picture: note the feathery branch shape and the downward hanging cones, Morgan Street at Hoyt Street, Stamford CT January 2005


pictures: maturing summer cones, fall cones and last year’s cones Morgan Street at Hoyt Street , Stamford CT 2004

The human-imported nemesis of our wonderful hemlocks is the Asian hemlock wooly adelgids (Adelges tsugae). These tiny aphid-like insects, that cover themselves in a white, sticky goo that looks like marshmallow-fluff, were first seen on the west coast in the 1920’s. This wasn’t so bad because the big western hemlocks have some defenses against the invaders. But then in the 1950s’ the hemlock wooly adelgids showed up in Virginia and have gone on to threaten to whole northeast. These mean little bugs are carried by wind, birds, and small mammals, but also, unfortunately, by humans transporting infected stock. Further, I have to wonder whether improperly planted hemlocks, weak and susceptible to disease, have contributed to the spread of this plague.

Once a hemlock gets infected, it can be dead in as little as three years. An example of the damage: according to the Pennsylvania Game Commission, such huge amounts of the western Pennsylvania forest have been affected by the hemlock wooly adelgids that the northern flying squirrels had to switch habitats and move in with their southern cousins. Unfortunately, the northern squirrels, already in short supply, and stressed by change of habitat, can die from a pest carried by the southern flying squirrels.

The hemlock wooly adelgids are all over Connecticut; I see the nasty little critters in almost every hemlock in downtown Stamford, and the younger trees are looking poorly – yellowing foliage and large areas of die-back. Some of the smaller ones are dead.


pictures: summer needles, winter needles, new needles in May, detail of white stripes on needle underside.
Morgan Street and Hoyt Street Alley Stamford CT 2004-2005


pictures: the bad guys (hemlock wooly adelgids) Morgan Street at Hoyt Street, Stamford CT 2004-2005.

There is hope for the hemlocks, and, thus, the otherwise homeless northern flying squirrels and chilly moose calves. In nature, a prime cause of bug death is other bugs. Here, hope comes in the form of Pseudosymnus tsugae, a tiny Japanese lady beetle that likes to eat its countryman, the hemlock wooly adelgid. Many states have released thousands of these mini-heroes and are having good but slow results. Connecticut has released many of these good little guys but I have yet to see them in downtown Stamford. The other, more temporary, help has been our recent colder winters. While the harsher temperatures have not eradicated the bad guys, they have reduced the numbers. I haven't seen a report of the effect of the cold on the Pseudosymnus tsugae.

So what can you do at home to save the hemlocks and, thus, the wild critters who depend on them?

As with all plant pests, indoors and out, the first line of defense is good culture. “Right plant in the right place” may be a tried, old saying but it’s only too true. If a plant that you want won’t grow well naturally where you want to put it – don’t try to force it with chemicals, unnatural amounts of water, and other environment- and kid-harming crap. Pick another plant that will do well at the location. The other half of this is: don’t plant a lot of any one plant.


pictures: This gorgeous mature hemlock is infected with hemlock wooly adelgids. Strawberry Hill Ave and 5th Street, Stamford CT 2004

The second most important line of dense is vigilance. LOOK at your plants frequently. Usually, this is enjoyable and good for the spirit. However, if there’s any kind of bug, you can get it early before it becomes a problem. In this case, though, should you see the nasty little guys, you need to check with your state agriculture authority to see if there’s a quarantine in force and if the tree needs to be destroyed for the good of the community.

If left to your own devices, think about destroying the tree anyway, if it’s not properly planted (e.g. in full sun or a place that’s too dry or too wet) or very sick. Why prolong a problem and let your yard become a haven for bad bugs that can spread? If you do pull the tree out, depose of it properly so you’re not spreading the disease via the town dump.

If the tree’s a good one in a good place and the infection is minor, you can prune out the dead parts and give supplemental water during dry periods. Mulch well. Get a $15 (or free) soil test, and fertilize sparingly only if and as needed. Never over-fertilize a sick plant – this can push the plant to use up its last reserves trying to grow. Instead, hope for Pseudosymnus tsugae and a cold winter. Don’t be lulled by a local arborist or landscaper into repeatedly dumping expensive and harmful chemicals (pesticides and fertilizers) all over the place. It’s better to pull out the tree than to risk killing the Pseudosymnus tsugae and other beneficial insects which could save your tree and the neighbors’ from this and many other insect pests.

The general anti-chemical message notwithstanding, for individual trees small enough to be sprayed, some people have reported excellent results with insecticidal soaps and horticultural oils. However, these produces will do more harm than good (including to your lungs, wallet, and the Pseudosymnus tsugae) unless used properly. There are very short time seasonal windows when the stuff will adversely affect the bad insects – the rest of the time you’re throwing away you money, and possibly killing the Pseudosymnus tsugae.


First picture: To the left is a Japanese yew (taxus ) and to the right, a hedge-clipped hemlock.
Note the taxus needles are shinier, flatter, greener, larger and arranged much more neatly than the needles of the hemlock.

Second picture: Taxus are known for their red berry-like fruits. Taxus, which are more common than mud in the ‘burbs, are not affected by the hemlock wooly adelgids (or anything else for that matter, except perhaps snow plows, dogs, deer, and voles. Both pictures: Hoyt Street Alley, 2004.

All of the preceding pictures were taken in downtown Stamford where the hemlocks struggle with urban conditions. Now to show you what a happy hemlock living in the woods looks like, the following pictures were taken north of town in the Bartlett Arboretum, where there is no sign of the wooly adelgids.

pictures: happy young hemlocks in the forest understory Bartlett Arboretum February 6, 2005.
Note how green and shiny the needles are.

From The Monday Garden. Copyright © by Sue Sweeney. Reproduced with permission. 

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