Why it’s important to prune tree roots before planting

This week I discovered that one of our center’s landscape trees is ready to bite the dust. I was sad – but also happy.  It’s a wonderful teaching moment and if the tree has to give up its life to save others, I guess that’s okay.

As the video will show you, this Japanese maple was planted some years ago with a root circling the trunk.  As both the trunk and root have developed in girth, we’ve reached a point where the trunk is constricted and the weight of the tree is splitting this V-shaped specimen down the middle just like a turkey wishbone.  We’ll just have to see how long it takes.


Bottom line: even though it takes a little more time to correct a flawed woody root system, it’s well worth the effort.

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

14 thoughts on “Why it’s important to prune tree roots before planting”

  1. If you know it will fall over, aren’t you risking that someone will be hurt when it falls? It appears to be aimed at the street.

  2. You’re absolutely right, Greg – if it were a bigger tree, I’d worry about injury to people or property. In a perfect world, we’d remove it this fall and plant something else there. But I’m pretty low on the administrative-decision totem pole, so I imagine it will be there unitl it fails. In a perverse way, I hope this will happen, because it will provide me with even more photographs to use.

  3. Good information. I have a mature birch tree with a root like that. Is it too late to cut away the offending root and allow the trunk to expand somewhat normally?

  4. Alan, great question! Arborists have had some success in cutting vertically through the offending root to relieve the pressure. Continued trunk growth will pop the root at that split and force the cut edges away from each other. It’s certainly worth a try – just be sure not to cut into the trunk itself.

  5. It would be fascinating to air spade around the tree to see the whole picture. Especially to see how deeply the tree is actually planted and more of the root morphology/architecture.

  6. It would be great to see that, Alison. I’ll see if I can arrange to be present when the excavation is done and take lots of pictures. I don’t think we have an air spade, but maybe it could be dug out carefully.

  7. Interesting subject and one I just wrote about a couple days ago on my blog. I was mostly taking about deep root irrigation, but gave a plug on proper plants establishment and pruning those roots and correcting problems at the beginning not later. I made the illustrative co
    mparison to raising children. If problems are not nipped in the bud so to speak early on, there will be bigger problems later on in adolescence. Before moving to Sweden almost 7 years ago, i had a neighbour with a huge fruitless Mulberry tree with a giant splits and the same girdling problem. He refused to cut it down and replace it, so instead took ropes and chains and tied around it. Of course he had been pruning it like many who chop off all branches to a nub at the end of the year. Believe it or not it was still there last year when I visited. I also at the same time plant 6 inch high California Sycamores at my mum’s place and they have surpassed in growth his tree. I even offered them one at the time. Problem is people want instant landscape and 5 to 15 gallon trees are their choice. But root spinning is a huge problem and should be dealt with at planting.


  8. The circling root and undersized trunk are evident in the photos, but please consider that Japanese maples are weak wooded and prone to such injuries. So, the damage might not be caused by the root at all. We should be open to considering other reasonable causes rather than only the obvious one.

  9. We have mountain property that was burned in a forest fire in 2012. We are trying to replace the lost trees with low cost state nursery provided seedlings and some others that we started from seed. We recently learned about air pruning and are curious as to whether we should attempt to correct the nursery seedlings (in the long plastic tubes) or instead worry about correcting the roots at planting time this fall. Suggestions? Some of the nursery seedlings are 12-15 inch Ponderosa in short, 6 inch diameter plastic pots and must really be thick with circling roots.

    1. Dave, I’d wait until fall to correct roots. You have a longer uninterrupted time for them to regrow, and the trees will be dormant. If they are impossible to untwist, simply cut lengthwise through the mass and spread the two halves apart. I did this in another post on the blog (look for posts on lavenders to see photos).

  10. Just came across this helpful post, and this wonderful blog. Root pruning is such a vital topic horticultural topic and such a necessary one for gardeners and casual homeowners. Even fewer people have heard of root pruning than grasp the necessity of pruning young trees for correct branching. I’d gardened and planted trees most of my life before I became concerned/began to notice stray information like this. Keep up the good work!

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