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As a side mini project from a bigger patio project, we moved some concrete blocks to create a well around a tree in the front of the house.

A conversation over in DIY.SE chat this morning sparked concern about killing the tree by doing this.

Is what I have done detrimental to the tree? I've only raised the soil level about 6-9 inches; I will probably tamp the soil down, lay some landscaping cloth and fill in with crushed marble.

I'd hate to rip it all out, but if its going to kill the tree...

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    I'd move the entire ring to the back yard. Now you have a firepit! (What you have may not kill the tree, due to it's relatively small size, but it's definitely not healthy for it.) – DA. Apr 30 '13 at 19:07
  • diy.blogoverflow.com/2012/08/… built that last year, this year, a fireplace goes into my patio plans that i'm working on now - these blocks are no longer needed, but i can't throw them away... – lsiunsuex Apr 30 '13 at 19:09
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Well you're right to be concerned. The soil level around the base of a healthy tree should preferably not be raised at all, but if you must, 2 inches of something very light and free draining you might just get away with. However, because you've got a closed in 'well' around the base, it doesn't sound as if any soil there will be particularly free draining. The problem is because the soil may/will cause rot and fungal infections in the base of the trunk (which is supposed to be exposed to the air) because it is now buried. Infections like this at the base of a tree do cause plant death.

  • "2 inches of something very light and free draining you might just get away with" - So what if I take out the soil I filled in the well with, bringing the ground level back to what it should be and fill in with a mulch? Water will be able to penetrate the mulch and I'll still get the look of the well being filled in. – lsiunsuex Apr 29 '13 at 11:57
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    But you said you filled in to a depth of 6-9 inches with soil. If you take that out and put a mulch of 2 inches, you'd still have a big drop from the top row of bricks. Personally, I'd remove the 'well' and the bricks altogether and leave the tree just as it was before. – Bamboo Apr 29 '13 at 14:09
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You might be able to get away with this because the surface are you have covered is less than 25% of the total surface area where the tree has roots. Putting a thick layer of soil on top of an existing area is like putting a blanket over your nose. You can still breathe but it's hard.

As Bamboo says the other issue is using soil. You could increase your chances of success two ways:

  • take out the soil. Add several sections of 4 inch drain pipe with sleeve and use crushed gravel or large diameter river stone with one or more layers of landscape fabric to prevent weeds from rooting. This allows some air circulation.
  • take all except one or two inches of soil. Topdress with another inch every spring and raise it slowly. this lets the tree grow roots in the raised area

I don't want to be a party pooper but it appears you have built this in an area which, in many North American cities, is city property. The city owns six feet or more adjacent to their road. You may or may not have permission to do this. If your city has bylaw inspectors you may find yourself having a chat with them.

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    The city does own the first 6 feet (up to and including the sidewalk) but only in that, they have right of way; if the street needs to be widened, repairs done, its theirs to do with as they please. That being said, other houses on the block have "dressed up" this portion of their lawn so I'm not worried. IE: I'm not the first one to do it here. – lsiunsuex Apr 30 '13 at 19:13
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Raising soil level around a trees root flare is detrimentally identical to planting too deeply. Humans assumed trees produced Oxygen as a byproduct, but actually its an essential ingredient utilized by their root system just below ground. When these roots get smothered by Mulch or added soil, they act like drowning swimmers and immediately come up for air above obstruction. And just like disoriented swimmers, many times these rising roots end up growing toward trunk instead of radially away. If walled in like topics example, rather than dive below obstruction to get past it, roots will take easiest route and stay near oxygen supply while inevitably circling around trunk.

All combined, these detrimental effects will rot out soil moist trunk defenseless to insects and disease, along with producing "Girdling roots" which will inevitably strangle trees stem. Causing portions of crown to die off, or worse becoming public safety issue after constricted trunk snaps off from its base! Make sure tree is installed at "Root flare" level or two inches higher. Are you "Killing your tree's beautifully"? I suggest watching "This old house tree mulching" video on YouTube to become more educated about subject!

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I see another problem. The town may disallow your structure between the side walk and the road. You might literally have put stone on property you do not own. They might ask you to remove. And as for the tree, it's destined to be cut by the town crew in the future, unless you selected a small tree like Japanese maple, etc. The town is one day going to cut this tree. So, the location is the greatest danger for this tree.

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