It's high time I post an entry on one of my favorite evergreen trees, Tsuga canadensis or Canadian hemlock. The allée below was taken at Longwood Gardens, not far from the entry.
I love the willowy nature of hemlocks -- some coniferous trees like spruce can seem so rigid and stiff - but hemlocks have a softness to them that is unique. It's also native to the mountainside forests of this region which adds to the plant's advantages.
The short, flattened dark green leaves are easy to identify if you look for the white stomatal stripe that appears on the underside. The leaves are generally arranged in two ranks along the stem, with a third, smaller leaf compressed on top of the stem. The cones are small - smaller than a ping pong ball.
In the image above, you more clearly can see the shorter, third leaf. You will also notice that this leaf appears "upside down" -- that is, the side with the stomatal stripe is facing up. You also have probably identified the evidence of wooly adelgid on the branches. The white, cottony substance on the stems are egg sacs of the pest. Wooly adelgid was introduced to the US in the Pacific Northwest in 1924. It's estimated to have reached the Middle Atlantic states by the 1950's. Tsuga is the pest's food of choice and over the years, hemlocks will eventually die from an infestation. Until then, they will appear grayish in color, as the insect has sucked most of the sugar-rich chlorophyll from the leaves.
The specimen above is a weeping cultivar of hemlock. The most famous weeping cultivar is called 'Sargentii.' These are extremely slow growing (read: expensive) plants and in my opinion, they're somewhat strange-looking. Of course, my students already know that I have a bit of a bias against dwarf or weeping conifers.
Finally, Tsuga is not the genus that Socrates purportedly died by. That plant is called poison hemlock or Conium maculatum. The common name hemlock was applied to Tsuga because, as legend has it, early settlers thought the crushed leaves of Tsuga smelled like Conium.
One of my favorites as well. I have a beautiful 70 ft. specimen growing about 10 ft from the side of my house. The wooly adelgid is rampant here in Western NC and treating them for the infestation is mixed bag of results. I have been treating mine for about 5 years now. I love the tree for its own sake, but I selfishly have it chemically treated so a 36" diameter tree doesn't fall on my house.
ReplyDeleteI have noticed that one of the biggest influences on the adelgid's success is drought. For 8 years, we were in a horrible drought for our region. We lost many hemlocks - most in the forests where they could not be readily accessed (The massive hemlocks of the Joyce-Kilmer Forest are all but gone). Over the last 2 years, we have had a wetter, more normal, weather pattern. I have seen many hemlocks (mine included) come back with darker greener needles and a fuller canopy. When the tree isn't competing for moisture, it's health dramatically improves. Love this tree and I still specify it in plans with the hopes that genetic diversity will prevail over the adelgid.
Thanks Matt for your comment! I had a feeling this was a favorite of yours, too! And it's definitely true that any infestation is worse in times of drought (pests, that is. Of course, the opposite is true for fungal disease).
ReplyDeleteOh - I forget to mention its kissing cousin the Carolina Hemlock (Tsuga caroliniana). It is a rarer find here, and seems to be even more susceptible to the adelgid. It's needled whorl (maybe the wrong word) around the stem instead of being in two flatfish planes like T. canadensis. I have only run across is a few times in the wild and even rarer in the garden.
ReplyDeleteI live essentially across the street from what used to be the southernmost hemlock-mixed hardwood stand in New Jersey. But in the 18 years I've lived here 95% of the hemlocks have died off. Only young ones growing right on the banks of the stream have survived. Such a shame, and a loss of an extremely beutiful tree!
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