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Maintaining Thuja Green Giant at 15 feet high #872108

Asked June 07, 2024, 3:49 PM EDT

Two years ago I had 12 green giants planted along the border of my lot in a sub-division in SE Michigan. The goal in planting them was to provide privacy. When planted they were 6 - 8 feet tall and are now around ten feet tall. I don't want them to reach their natural height of 50+ feet and would like to maintain them around 15 feet high. Can I achieve this by pruning and topping them annually?

Washtenaw County Michigan

Expert Response

Hello

You can clip or shear them but if you cut into the  bare wood trunk they may not fill in properly. ‘Topping’ cuts into the woody trunk and opens the plant to disease. However, there are examples of maintaining them at desired height successfully by pruning every year.

Now that they are there, try maintaining them at your desired height and width. Be sure the tops are slightly narrower than the bottoms so that the bottoms, where your visual screening occurs, doesn’t’ get shaded and begin to thin.

See the advice on pruning arbs here-

https://s3.wp.wsu.edu/uploads/sites/2076/2021/09/C111-Pruning-Evergreens-format-update-21.pdf

And shaping evergreens so the bottoms are not shaded, here—


https://extension.umd.edu/resource/pruning-shrubs-and-hedges-home-garden/

I have seen an example of arborvitae that are maintained at a static height by clipping them 2-3 times per year(the hedge I have seen is maintained as a topiary would be, clipped into a geometric rectangular shape)

There are arbs whose mature height is about 15 feet, should you end up having to replace yours. One popular arborvitae (Thuja occidentalis) is ‘Emerald Green,’ also known as ‘Smaragd’, which matures at about 15 feet tall by 4 feet wide.

https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderProfileResults.aspx?basic=Thuja+occidentalis+%27Smaragd%27

Thanks for the reply. Right now the trees are planted 12 - 14 feet apart on center. Would adding adding another green giant in between the current trees, to make the spacing 6-8 feet on center, help keep their size down? 

The Question Asker Replied June 10, 2024, 9:28 AM EDT

Thanks. Can you share a picture or link of a thuja green giant hedge that is maintained at 15 or 20 feet high?

The Question Asker Replied June 10, 2024, 12:50 PM EDT
Not specifically Green Giant, but here is one example of a Thuja hedge from an earlier question. While the client says “top them” more accurate would be ‘prune them’  The answer indicates that dormant buds do exist on old wood, so pruning into it maybe acceptable. 
https://ag.umass.edu/home-lawn-garden/photos/trimming-arborvitae

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