Two Ways to Prune Cedars

I have lots of cedars and a pretty small plot of land, so I’ve had to learn how to prune them. I have so many because they stay green all year, they’re easy to care for, and they create much-needed privacy in my urban garden.

I believe all of my cedars are Emerald Cedars (Thuja occidentalis ‘Smaragd’) but I don’t treat them all the same. I keep one looking natural and the others I’m slowly transforming into more formal clipped cedar hedge walls.

 

Pruning to Maintain a Natural Shape

The one cedar that was in the yard when I bought the house more than fifteen years ago–it was about 4′ high at the time–is now a towering 20′ or more. I’ve kept it from swallowing the path beside it by continually pruning it back in a way that maintains its natural shape. I want it to continue to look like a cedar tree (classic pyramid / Christmas tree shape), and not sheared topiary.

To do that I carefully prune back extra fullness in the same way that I’d trim the branches of a deciduous tree–going back to where one branch comes off another, and making angled cuts.

 

This is way more time consuming than just shearing everything off like you’re using a lawn mower, but it’s the only way I know to maintain the natural shape of the tree.

 

I made a short video to show the process in action as well:

Pruning Cedars to Create a Formal Hedge

After kicking myself for not creating a solid cedar hedge at the back of my property years ago, I’ve been slowly transforming the cedars I eventually planted into a solid wall of green along the back fence, in order to hide the chain link fence and not so lovely garage behind me.

This was the scene in my yard last weekend. You can see the three cedars on the left that I started with, and started shaping a couple years ago, and then, on the right, three newer cedars that I was allowing to get some height before starting to trim them. There’s also a single columnar juniper in front of the cedars. The wooden structure in the picture, if you’re new to this blog, is part of my tomato support system.

Because these cedars grow right along the edge of my vegetable garden I find the easiest time to get a ladder near them in order to prune the tops of them is when the ground is frozen. We usually have a few sunny and not too cold days in the winter when I can get out for an hour or two and feel like I’m gardening again.

 

The most critical part of a nice looking formal hedge is to have the tops of the trees reasonably even. I don’t think I’d do a good job eyeballing this, especially when I’m up on a ladder and can’t just step back to see if it’s straight. So I use a stick with a line on it, that I place on top of the back fence as I go along, so I can see where my cuts should be. If your trees are planted on level ground you could do the same thing with a long stick, or even a tape measure, measuring from the ground up.

I line up my secateurs on the tree with the line on the stick, and make a cut.

Once the first cut is made I can then trim the rest of the tree to match that height. I don’t get fussy, like when I’m trying to maintain a natural look, but just go across like a lawnmower. I use a pair of hand secateurs to do this work as I don’t have a large number of trees (and my larger hedge shears are locked in the shed, behind a door that is now frozen shut.)

 

For the three trees on the left, this was really just a little trim off the top. For the three trees on the right, I was actually cutting the tops off (sometimes called “topping” a tree).

 

This involved cutting the top off the trunk. Since this was a thicker piece of wood, I made my first cut straight across. Then, once I could see a little better, I went back in and made a clean angled cut.

 

When you’re shearing a hedge, you don’t have to do this with every cut, but for a significantly sized piece of branch like this, I think it’s good practice.

I’m going to keep these trees fairly narrow in depth for two reasons. One is that I don’t want them to encroach onto my vegetable garden or block any more light than necessary, and the second is that I don’t want a large flat surface on the top. In a climate like mine that gets reasonably significant snowfalls, I need to keep as much of my hedge angled as possible. I can and usually do tie them up every fall in order to prevent damage from snow and ice, but building a proper structure goes a long way to keeping them intact as well.

Speaking of which, the vertical shape of a hedge (all hedges, not just cedar ones) is important too. A hedge that’s going to be healthy is narrower at the top than at the bottom–this allows sunlight to get at all parts of the plant. Whatever parts of a cedar tree that aren’t exposed to light will die (you see this on the inside of older cedars, near the trunk.) The only exception to this is when the hedge is grown in a spot that gets direct sun (e.g. the edge of a farm field, or a country estate, where there’s nothing but low grasses or roadway nearby.)

While I was pruning last weekend I only trimmed the top of my hedge because that’s the only part I need a ladder to reach and do a decent job.

 

I’m going to wait until my shed door thaws so that I can get my hedge shears out, before I trim the sides of the hedge. When I do, I’ll just shear them back like I’m using a lawn mower. This was a little scary the first time I did it, as I could see somewhat open bits as I did this. But I’d read, and it turned out to be true, that cedars do fill out once you expose those empty spots to sunlight. I was cautious though, and haven’t made really drastic cuts, but am slowly narrowing the depth of the hedge year over year. It’s almost exactly where I want it now, so my yearly trimming will become like a regular haircut–just a little off the top and sides!

My goal is to have a hedge that looks like this one (except a bit narrower) in Quebec.

 

4 Comments

  1. Jim Allsop on February 28, 2019 at 9:02 am

    Jennifer as a certified arborist with the ISA

    • Jim Allsop on February 28, 2019 at 10:02 am

      Sorry Jennifer hit the send button by accident before I had a chance to finish.
      As a certified arborist we are taught to not prune any woody species below -10°C as the wounds do not heal and further infections are possible. In your picture I see snow on the roof and hence it is not the right time to be doing pruning on any woody species. Pruning wounds do not heal at this time of year the tree is dormant.

      • Jennifer on March 3, 2019 at 7:49 pm

        Thanks for your comment Jim. That’s interesting as I’ve always understood that pruning trees when they’re dormant is the least traumatic timing for trees, and promotes the most growth (prune in winter for growth, prune in summer to keep small), and never heard that the temperature while dormant was a factor. Thank you–you’ve given me something new to research and learn about further!

        • Jim on March 4, 2019 at 8:38 am

          Good morning Jennifer one other little bit of FYI depending on the species of tree the time of pruning is critical to the tree health.

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