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Downsizing Arborvitaes #745950

Asked April 23, 2021, 5:26 PM EDT

Will it harm my Arborvitaes if I cut them down from about 12 feet high to about 7 feet high ?

Charles County Maryland

Expert Response

Arborvitae (Thuja) will withstand heavy pruning and shearing because new branches develop from concealed buds in the branch crotches. Prune in early spring or mid-summer.

  • When heavy pruning is necessary, prune before new growth begins in early spring so that new growth conceals pruning cuts.
  • To lower the height (no more than 20 percent) of a plant, cut back to a lower branch crotch, making cuts only into live wood. To regain the natural shape of the plant, balance lower limbs by lightly pruning branch tips.
  • Older arborvitae growing in shade will develop a dead zone that is incapable of regenerating new growth. Do not prune into this area.
  • Oriental arborvitae (Thuja orientalis) is slow growing and responds best to shearing new growth only.

Hope this helps.

Taffy Replied April 26, 2021, 2:40 PM EDT
If I downsize the arborvitae by 20 - 25 percent this summer will they eventually grow back to about 12 feet or will they grow back somewhat less than 12 feet? I have forgotten exactly what type arborvitae they are but they are not the Oriental type. They are in full sun and we're planted in soil rich in compost. Regardless of how much I prune them they grow like a wildfire out of control.  I want  to find a way to permanently shorten them so I do not have to prune them so often. I do not want to cut them down because they are in brick planters and the stumps cannot be removed unless the planters are demolished. Is there any way to make them permanently shorter?


On Mon, Apr 26, 2021 at 2:40 PM, Ask Extension
The Question Asker Replied April 26, 2021, 4:05 PM EDT

Unfortunately, there is no way to permanently stop a plant's growth.  If you want these plants short, you will have to prune them every year.  This is a good example of the need to do research on plants before you buy them to find out their mature size.  It appears you have the full sized variety, Thuja occidentalis, native to eastern North American which grows to 20-40 feet. If you decide to take these out and want to plant Thuja occidentalis that stays small, here are some suggestions: 'Little Giant" grows to 4 feet, "Skinner Dwarf' grows to 7 feet, "North Pole" grows 10 - 15 feet.  

Taffy Replied April 26, 2021, 5:18 PM EDT
Will it kill the arborvitae if I downsize them more than 20 percent? What is the maximum I can take off the top without killing them?


On Mon, Apr 26, 2021 at 5:18 PM, Ask Extension
The Question Asker Replied April 27, 2021, 5:08 PM EDT

They won't immediately die if you take off more than 20%.  But they will look scalped.  It will make them the height you want, and maybe it will take longer for them to get to their natural size but it will stress the plants.  If they keep getting stressed, they will stop growing, as per your original question, but that means they will eventually die.


Taffy Replied April 27, 2021, 6:13 PM EDT
Question answered completely. Thank you.


On Tue, Apr 27, 2021 at 6:14 PM, Ask Extension
The Question Asker Replied April 29, 2021, 3:49 PM EDT

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