How To Prune Arborvitae ‘Green Giant’

How-To's, Landscape Care · Written by Roger


shear.arb.ggThe Green Giant’s Growth Habit

Perhaps I’ve said it before, but it’s extremely helpful when you know what a plant’s growth habit is before you prune.  Growth habit is basically the shape a plant naturally wants to grow into and how the branching structure supports that shape.  For example: Arborvitae ‘Green Giant’ is pyramidal in form and proportionately much taller than wide.  As a matter of fact, this plant will easily get to 30′ tall and 15′ wide in thirty years.  Rapid grower…I think so.  Its branching structure is horizontal with some ascending branches as well.

Other characteristics about the plant can be helpful too when deciding your pruning strategy.  For instance, Arborvitae ‘Green Giant’ prefers more light (full sun is ideal).   The less light it gets the thinner and more open its branching and foliage will be.  Prune less aggressively if you know the plant is adapting to less than ideal conditions.

Before Pruning

The Pruning Strategy

Let’s assume the ‘Green Giant’ you’re going to prune has been positioned to have enough room to grow and stay somewhat within its “natural boundaries”.  If the space is too limited and there’s no future for the plant in that spot, think about transplanting it.

To give ‘Green Giant’ a strong trunk and branching structure, it’s important to prune them in their early years.  In the first picture above, these Arbs were undoubtedly pruned early on in their lives.  Notice how full they are from the ground to about 4/5ths of their height.  However, the last growth at the top is thin and “stretched-out”.  This is very typical of rapid-growth plants.

It is this top growth (upper 1/5th) that needs pruning.  You should also scout the lower portion of the plant for any branch ends that may have grown more aggressively than others.  There should not be many.

After Pruning

I apologize for the picture quality of these “before” and “after” shots, but even the silhouette conveys the degree of pruning I did.

I used a traditional trimming shear along with an orchard ladder.  By today’s standards you might call that “old school”.  I still think a good quality hand shear gives the best cut and, of course, with total control.  I did, however, think how convenient and productive a telescopic gas powered shear would have been.  Just take care as those power shears can cut aggressively.

The main goal and concept here is to trim the ends of the longer, fast growing branches to shape the plant and encourage fuller growth.

This is what plant nurseries do while they’re growing the plants for market.  You want to continue this trimming routine for as long as it is practical.  The idea is to develop a full, nicely shaped plant so that it can continue to grow on its own with this strong foundation you’ve help create.

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    109 Responses to “How To Prune Arborvitae ‘Green Giant’”

    1. Jim v Says:

      I have a row of Arbs which were present when I bought my house 14 years ago. They are now a nuisance to my gutters. I don’t want to give up the “natural” fence between my neighbor and I, as their lawn care leaves much to be desired. would it be okay to trim them from about 15-20 down to 10ft? transplanting isn’t an option, since there is a gas line and sump pump line within 3ft of the base of the trunks for about 75% of the length of the row.

      Also, I have another row which is encroaching on my driveway on the other side of my property. I am contemplating removal of those trees as they are 20 ft tall as well and trimming them back at this point will leave them quite bare on the southern side. how deep does the root structure go if I were to decide to do this, or how aggressive can I be in trimming them back from the driveway? I would likely need to cut out about half of the radius on that side.

    2. Roger Says:

      As you’re suspecting, cutting the Arbs down from 15-20′ to 10′ is pretty extreme. I’d have to see them to give real guidance on how much to cut.

      The plants will survive the cut, but the uncertainty is how they’ll respond and look at the top where they’re cut. The Arbs naturally want to have a central leader that grows in height. You’re proposing cutting that back a lot and then essentially maintaining it there — for as long as you can anyway.

      I suspect the side branches just below your cut will push out growth (during the next growing season) and you can begin to “round-off” that top growth to keep the plant from getting taller.

      Please keep in mind this is just my opinion, and I have no way of being sure how your plants will react to severe cuts like this.

    3. Roger Says:

      I realized I did not comment on the second question you had regarding the Arbs along your driveway.

      Cutting half the radius of the plant’s branching would look terrible and likely not recover — at least to an acceptable appearance.

      The roots on an Arb that tall are approximately 24-30″ deep. And just like you’re aware of underground utilities with the others, I’m sure you’re considering the same with these. Also, I’m sure you’re taking into consideration the impact on the driveway. Loosening the base material (of the driveway) near the edges should be avoided if possible. You might have to do some preliminary “hand digging and root cutting” before you pull the stumps.

    4. freddie c Says:

      Can I keep arbs at 15ft tall? I don’t have much space between my property and next door..any advice?

    5. Roger Says:

      Over time it will be difficult to contain ‘Green Giants’ to that size. And not just in terms of height, but width too.

      You can put up a good fight by diligent pruning and probably get a good number of years of use out of the plant.

      There are also what are called “Plant Growth Regualtors“. These products get administered to the plant and control their growth. I have no personal experience with them.

      And, of course, if practical and cost effective, you could transplant the plant and replace with something more appropriate for that spot.

    6. Dale Says:

      What trimming technique could be used so that the top 3rd of the tree could become more full so that there is less gap between the trees? Thanks!

    7. Roger Says:

      If you follow my advice in the article, i.e. to concentrate trimming in that top third of each plant, they’ll fill in nicely.

      Make sure you prune back the terminal leader (main vertical stem) because this dominant stem wants to get taller each year. You’ll have to allow the plant to attain some degree of its height, but in the meantime you’re controlling the rate of the top growth and encouraging a fuller plant.

    8. cynthia Says:

      planted 3-4ft Green Gaints about 5 years ago…didn’t know about pruning doube leaders out so now I hav a lot in my row of 20 trees that are touching now and about 6-7 high…it it ok to prune the double leaders now?

    9. Roger Says:

      Of course I’d feel more confident giving advice on whether or not to prune out double leaders if I could see the plants.

      But here are my thoughts. With your Arbs at 6-7′ tall you could still remove one of the double leaders and the plant would have plenty of future growth to adjust.

      Where on the plants (in terms of height) is the double leader occurring? Upper half? Below halfway point?

      Again, I’d like to see the plants to guide you more assuredly. Can you visualize how the plant(s) will look right after removing one of the leaders? Can you carefully pull the one leader you’d remove slightly away from the other to give yourself a view of how it might look?

      I’ll leave you with this point in the event you decide to leave the double leaders. When we install Arborvitae that characteristically have multiple stems (e.g. Arb. ‘Emerald Green’), we automatically put a supportive band of ArborTie inside the plant 1/4 of the way down from the top. This prevents the stems from splaying apart due to age, wind or ice & snow. You could do the same with your ‘Green Giants’. If you do this, you must remember to monitor those “ties” at least once/year. They will need to be moved and/or adjusted every now and then. This is very important!

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