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When I bought my current house 2 years ago I inherited a beautiful mature 8' tall Japanese Maple (probably planted soon after the house was built in 1972). From outward appearances it seems to be vigorous and healthy. Here's a winter picture showing the structure.

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At some point, probably over a decade ago, the prior owners removed a large limb low on the tree but rather than pruning at the collar they left about 8" of stump protruding.

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I've had other things on my mind, but finally got around to really examining the tree and noticed the branch stump seemed to be rotting, so on advice of a local arborist I cut the stump back to the collar, where it should have been cut.

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The rot extends deep into the tree. An 8" screwdriver went in with no resistance. That means the rot extends into the main trunk heart wood but I can't tell how far it has spread there.

Question: Is the tree doomed in the near future, and is there anything I can do to preserve it or prolong its life?

Should I be doing anything to prevent accelerating damage, such as fill the hole to prevent water from entering, etc?

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There is nothing you can do to preserve or prolong its life in terms of the rotting heartwood in that branch I'm afraid. It might mean you lose the tree eventually, but that would happen anyway, as it does with all living things at some point. Whether it will actually hasten the tree's demise is hard to say - life is resilient, and it may go on for years despite this problem, but just keep a check on the tree occasionally to make sure none of the branches is becoming a danger in terms of suddenly breaking off and falling if the problem has spread.

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    That's kind of what I thought. The tree is only 8 feet tall, so there's not any danger to person or property. Should I try to prevent water from entering the rotted hole? Is there any "assistance" I can provide the tree? – Jim Garrison Mar 10 '18 at 22:19
  • Well hopefully you didn't make the cut so that it slants back towards the trunk as it goes up, thus allowing any rain to fall straight into it, but no, nothing else you can do to make any difference, no sealant or anything, that may aggravate the situation – Bamboo Mar 11 '18 at 0:51
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No guarantee, but I think by cutting that stump off to the correct length of the collar, the tree will be able to 'heal' the damage all by itself. More air, less water, less bacterial/fungal life. Plants are very conscientious about damage. They don't want to die just because of a scratch or broken limb/leaf...they have their own plans in place to take care of their health.

As long as that tree is healthy it should be able to deal with the rot now that there is air flow and less moisture.

I'd like to see a thin layer of soil covering the crown of the roots. Only up to the line where bark begins, no higher. You might have to change your walkway a bit but that tree is worth any work and expertise to learn to manage this gorgeous specimen. We could talk about ripping the concrete walkway out, replacing with pavers made of concrete; 2 inches thick set on a sand base worked around the base of this tree. Patio/walkway?

Think about a low voltage landscape spot light up lighting this tree at night...

I would leave this stump alone. Maybe get a hair dryer and try to dry it out a bit? Remove some of the tiny branches of leaves right at the main branch...open the canopy up somewhat to allow more air movement and light as well as great peekaboo glimpses of that beautiful structure. I always went under the canopy to prune. Leaves on little branches that hardly ever see the sun are a good thing to remove. When you remove them remember that you've now allowed other leaves more light access.

What did your arborist think of the cut? The little bit of rot? Very cool you hired an arborist, this tree deserves the expertise. Beautiful Japanese Maple. You do know this tree will never get any higher, really. 8 feet is huge for this little grafted tree!

It would have been better to have cut that stump off at a bit of an angle so water would slide off and away. I can't tell by the pictures. This tree should be just fine. The rot might have gotten into the tree but with more air your tree is able to 'cauterize' any access to the important cambium just below the bark. The interior of your tree will heal with more air. Do not stuff anything into that hole. The collar looks like the proper thickness and the wood looks healthy other than that center.

At 45 years of age or so this tree likes its location and will probably outlive us all. I'd love to help do a little pruning this spring with you on this tree...?

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Now that you’ve cut the stub back properly the tree should be able to compartmentalize the damage on its own. I would recommend drilling a quarter inch hole up into the bottom of the cavity at a steep angle. That way any water that gets into that cavity won’t sit there and hasten the decay of the damaged heartwood. It also looks like you have a girdling root going around the trunk of your tree at the root flare. That should be cut off as it restricts the vascular of that whole section of tree. Otherwise the tree looks healthy. You can wait until summer to see where it’s crowded and do a like pruning at that time to increase air and light penetration but don’t over do it as Japanese maples have thin bark and are susceptible to sun scald.

  • What do you mean by the bottom of the cavity? From what the OP says, the cavity extends into the main trunk, and its size is unknown. – VividD Mar 12 '18 at 6:38
  • Yes, the cavity is at least 8" long and could be a lot longer. I'll do some probing tomorrow with some stiff wire to see if I can find the bottom. As to the girdling root, I think I will have to get an arborist to do that. I wouldn't know where to cut and what to remove. – Jim Garrison Mar 12 '18 at 7:10

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