The Canadian Hemlock is one of my all time favorite upright evergreens. I use them in many of the landscapes that I do, including my own. They grow nice and full but are still easy to maintain at just about any given height you choose.
In a landscape planting I like to keep them at a height of about 6-1/2, maybe 7′. This is just tall enough that I can trim the tree without the use of a ladder. I frequently use the Canadian Hemlocks on a corner then accent the evergreen Hemlock with the brilliant yellow Gold Thread Cypress. But don’t over use the Gold Thread. Three around the front of the bed is good, then use another evergreen around the back of the bed. Something like Taxus Sebian, Taxus Densiformis or even Blue Girl Holly. Using the additional evergreens around the back of the Hemlock also provides an evergreen back drop for the Gold thread from different angles and really makes them stand out, but still not over the top with the yellow color.
When I trim Canadian Hemlock I use regular, manual hedge shears and all I do is tighten it up. Each time that I trim it, it gets a little tighter and eventually, over a period of years it gets so tight you can’t even get your fist inside of the plant. As a side note, I trim Rhododendrons the same way and they get just as tight! Nice and full.
Left untrimmed the Canadian Hemlock looks great for the first year or so, but what happens is the same thing that happens with all plants that are left un-pruned. When you leave a plant un-pruned the following year it flushes out with new growth in the spring just like it’s supposed to. But all of that growth is on the ends of the branches that should have been trimmed off the year before. Many people don’t realize what’s happening, don’t really know how to correct it, and before long the plants in their landscape look terrible. I’ve seen it happen time and time again.
Pruning is much simpler than most people make it out to be but some people really don’t like to do yard work so they simply don’t prune. Then when they do, they don’t prune enough to make up for the prunings that they missed. Others just can’t bring themselves to cut off much from their plants. I’m not sure if they are afraid they’ll hurt them, or if they feel that they paid good money for them and they are not going to cut away part of what they paid for. I’m not sure what all the emotions are that go with pruning or not pruning.
One of the emotions has to do with spousal issues and I’m not even going there. It’s not a gender thing, it’s a spousal thing. There’s always one person in the relationship that wants to prune and the other thinks he or she is a pruning maniac. To the point that they drag me or their father into the argument!
So whether you are pruning a Canadian Hemlock, a Rhododendron or any other plant in your landscape I’ll let you in on a little secret. The ideal time to trim any plant is when it needs it. If you wait, you might not get around to at the “ideal time” and next thing you know the landscape got away from you.
Like most evergreens Canadian Hemlocks don’t do well in really wet soil, but they can tolerate more shade than most other evergreens. But you should also know that I use them and grow them in full sun, so they are okay with that too. They do well in zones 3 through 8 and make an excellent evergreen hedge. However, they are slow growing and slow growing plants always cost more.