Cut in time: The best approach to pruning an arborvitae

Be brave

Keeping plants smaller than they can be is not a job for the timid gardener. The gold pyramidal arborvitae you see here has reached the desired maximum height and width. Now it must be cut every year or two. With the exception of one branch, the debris on the ground will be the normal amount to take from the tree each time. That branch is in the right foreground, a large limb that was a double trunk. It's a one-time removal.

How often

Every year or two? It's up to you, although it does also depend on whether the plant is large enough to lose more than one year's growth. If we want to cut less often, we cut harder. Remove two years' growth and we can let the plant grow two years.

Simple cuts

The cut is simple -- start at the top and cut every branch that's reached the limit to shorten it by at least one year's growth. That branch will have to grow all year to reach the line again.

One look at the branch tips tells us this plant is growing 4-6 inches per year, so we're cutting back that far. If you can't yet "read" a branch to learn its growth rate, look back at one- or two-year ago pictures of the plant and cut back to that size.

Essential: Thinning

Then thin, by cutting one of every four or five branches back even further. This admits light to the interior, keeping the plant dense. It also insures the plant will be more vigorous since it can keep some of the new growth it makes each year. How far do we cut back when we thin? The ends of branches we thin can often grow for three years or more before they once again reach the limit.

Janet's doing all the pruning with hand clippers to maintain a naturally fluffy outline. For a more tightly drawn profile, we could shear with hedge clippers (electric or manual) and then thin with hand clippers.

Here's the little cutie six years ago. New, and only as tall as the fence.

Here's the little cutie six years ago. New, and only as tall as the fence.

Three years ago. Just reaching the desired height. It's reaching the pavement, so we might have begun pruning at that point.

Three years ago. Just reaching the desired height. It's reaching the pavement, so we might have begun pruning at that point.

Last spring, after five years growing in this place. Definitely time to prune. Janet also notices a double trunk -- she's pulled it away from the main trunk and has it clutched to her chest while she decides if it can come out all in one go. It can.

Last spring, after five years growing in this place. Definitely time to prune. Janet also notices a double trunk -- she's pulled it away from the main trunk and has it clutched to her chest while she decides if it can come out all in one go. It can.

Please note the snowshoes...

...in that last photo. If you've been with us a while, you've seen them before and can skip this next note. If our snowshoes are news to you: Late winter is a good time to prune but a bad time to walk where soil is wet. Under the pressure of Janet's work boot, pressing down with 4 to 80 pounds per square inch depending her stance, the saturated soil atop still-frozen layers below will squish like a peanut butter jelly sandwich. You know that sandwich can never be fluffed again; neither can that soil. So walk on plywood, strap bundles of yard waste bags to your feet, or wear snowshoes.

 

In the next photos you see the little arb right after its March cut, and in June of the same year. Doesn't look like it was pruned? Good. Now look back at its three-year-ago picture, and see we've cut it back to that size. We've also refined its edge so it's a narrower pyramid. That shape will hold for two years, then we'll do it all over.

Total elapsed time, including the initial assessment, a discussion of if we should cut, the convincing of the client that the double trunk should go and the shrub would be fine and still beautiful, plus all debris clean up: 60 minutes. In the future, we expect 30 minutes' work every two years.

Immediately after the cut. A little thin on the right, where the double trunk came out.

Immediately after the cut. A little thin on the right, where the double trunk came out.

Ten weeks later, its winter gold muted in summer and lost to the camera in the afternoon shade.

Ten weeks later, its winter gold muted in summer and lost to the camera in the afternoon shade.