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We have a Mt Fuji, Prunus 'Shirotae', tree with a total diameter of about 8 meters (26 feet). We only have a small garden but love this tree. It's planted next to a brick retaining wall (goes down to our driveway). For a long time it's been fine but it finally started pushing out the retaining wall with a large root. The trunk is about 20cm (8in) in diameter and the root must be about 10-15cm (4-6in), so it's a major one. I'm sort of okay to just leave it and let nature take its course but an alternative would be to slice out the outer part of the root which is against the retaining wall. How bad would this be for the tree?

Overview of area:

Overview of area

Problem root:

Problem root

Looking in more detail, I now see that the tree itself is probably pushing a bit now on the retaining wall. I think the only solution is to actually remove the retaining wall and perhaps rebuild it to suit the tree. Suggestions?

Retaining wall:

Retaining wall

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    How does the damage to less than a third of the diameter guide apply to roots? – Wayfaring Stranger Sep 29 '16 at 14:30
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    Welcome ioquatix. I see you've already gotten some good advice, but it would be great if you could add some pictures. An overview of the area and one especially where it's closest to the retaining wall, would be the most helpful. Thanks! – Sue Sep 30 '16 at 1:06
  • @sue as you suggested I've added detailed photographs. – ioquatix Sep 30 '16 at 2:27
  • Those are great pictures, thanks, among the best I've seen! I wish I knew how to do those labels and arrows! Unfortunately, I'm not a tree expert so I don't have anything more to offer, but it looks like kevinsky and the others have helped you. Future visitors will find this an awesome question, detailed, easy to understand and fully illustrated. Can't ask for more than that! Thanks! – Sue Sep 30 '16 at 15:23
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If you cut the root you will damage the leaves that are fed by that root. That root also provides structural stability.

A better idea is to rebuild or remove the retaining wall in that area. The root will only get bigger and they can move quite large stones and interlock.

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    kevinsky, I went and actually looked up the vascular system of trees to check this 'root to leaves' xylem system and couldn't find a more detailed 'plumbing schematic'. I do believe that the roots take up water/chemicals and the xylem is one big pipe where all the water is accumulated and then distributed to the most productive parts of the tree needing water. If one root supplied water to one branch when the tree decided that branch was not doing enough work making food, if it abscised that branch/branches then it would follow there would be a dead root as well. Doesn't happen that way. – stormy Sep 29 '16 at 20:14
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    I agree, I would rebuild, restructure the wall to accommodate the tree. That tree is worth far more than a few bricks and a mason's time! I would not chance messing with roots, as Kevinsky said, support is a factor and the tree would be stressed. If this were just any old tree I would cut the roots off that go toward the wall or concrete. Cherry trees are far more susceptible to disease than most trees. Especially the fungal diseases. Your tree is highly prized and must be happy as it is. Fix the wall, don't mess with the tree! – stormy Sep 29 '16 at 20:34

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