Canadian hemlock, Tsuga canadensis, also called hemlock spruce and eastern hemlock is another of the East’s mighty evergreens. It is the state tree of Pennsylvania. Trees can live 500 years, grow from 100 to 170 feet tall and be five to six feet in diameter. Rickett’s Glen State Park in Pennsylvania has many of these behemoths of the forest.
They are shade tolerant and if the canopy is closed will bide their time until an opening occurs and then they will have a growth spurt. My fifty year hemlocks are only about 12 feet tall. In one section of Woodland Park there are some tall old hemlocks; magnificent specimens as well as a small grove up the hill from me. Hemlock does not make a good Christmas tree because it does not retain its needles. Oh that it would!
Hemlock bark contains a lot of tannin useful in converting the hides and pelts to leather. There were so many trees that many hemlocks were cut down, stripped of their bark and the logs left to rot. After all, the supply seemed inexhaustible.
Unlike pine, hemlock is easy to prune and can make a dense hedge. On one of my garden visits I saw such a hedge that was probably 12 feet high. A neighbor maintained such a hedge for years albeit only 5-6 feet tall. I had a hedge, but in such dense shade that the lower branches died and I finally removed all but two of them...
Early on I became interested in dwarf conifers, especially dwarf hemlocks and acquired a few nice specimens. They were doing great BF (Before the Fence) until the deer discovered and wiped them out one winter. Since I erected the fence I have added a few more. Dwarf only means slow growing and some can eventually overpower their allotted space. But as I remarked earlier they are easy to prune and therefore can be maintained at a comfortable size. My favorite dwarf is ‘Cole’s Prostrate’ which I was able to buy a few years ago. When I bought it, I had a special spot for it; at the corner of the wall leading off the patio. Here it can spread in all directions lying low and draping over the wall. Each year it will drape another inch or two adding more interest. One plant after 25 years was but 6 inches tall and 40 inches wide.
In contrast ‘Sargentii’ is a pendulous form which grows upright before draping. A few years ago I saw one such specimen at Longwood Gardens that must have been 10 feet in height and 30-40 feet wide. Not a hemlock for the average home garden.