Tree ring

In our circular driveway we have a border around a 20' tall Queens Crepe Myrtle tree made of a few 4x4 landscape lumber tied together with metal angles. We are going to change that to using retaining wall bricks.
One question is the wall would be a foot higher than the current height of the 4x4s. I am thinking may be I need to fill in some soils inside the ring to bring that up 6 inches or so. Would doing so hurt the tree in any way, adding 6 inches of soil and another 2" of much at it's base?
I am going about 4 bricks tall, each brick 8 inches tall. The guy I was talking to that may help me install this says there is no need to use mortar in between each brick all we need to do is to have some sand base and stack them up. Is that the case?
Thanks,
MC
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It's already bad enough that the tree is surrounded by pavement, adding soil over it's roots is as bad an idea as paving right up to its trunk, you will very likely kill that tree. You can swap the lumber border for masonary but do not fill it in... and ideally the opening in the pavement should be at least the diameter of the tree's drip line when it matures, now is the time to enlarge that opening.
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I cannot open the pavement up. The tree drip line does extend beyond the soil area, which is somewhat of a semi-circle. Outside of that is the driveway, then the house. The driveway is just about the right width for one car, and it's a concrete driveway, so making the soil area any larger is not practical, unless we want to lose the driveway altogether.
So I will not raise the soil level, and just replace the semi-circular wood border with a brick border. The other problem I have is that when it rains in Miami, the rain occasionally floods the streets and the wood border "floats" out a few times. I had a few rebars securing it, no matter, it still lifts a bit.
Thanks,
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In our circular

I cannot open the pavement up. The tree drip line does extend beyond the soil area, which is somewhat of a semi-circle. Outside of that is the driveway, then the house. The driveway is just about the right width for one car, and it's a concrete driveway, so making the soil area any larger is not practical, unless we want to lose the driveway altogether.
So I will not raise the soil level, and just replace the semi-circular wood border with a brick border. The other problem I have is that when it rains in Miami, the rain occasionally floods the streets and the wood border "floats" out a few times. I had a few rebars securing it, no matter, it still lifts a bit.
========= I've seen similar situations where folks extended the size of the opening for a tree by having an iron shop make up decorative wrought iron latticework panels, like slices of pie, with legs so they all sat in teh hole evenly level with the driveway yet could support the weight of a vehicle... would be a lot more attractive than cheapo cast concrete blocks from Lowes... could even set a decorative iron bench around the tree trunk.... you can pose there with a mint julep and oversee your estate like Rhett Buttler. hehe
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MiamiCuse wrote:

ISTM that you should not change the soil depth around the trunk of the tree. I would recommend that you leave a circular area around the base of the tree where the soil level is not raised. This circle should be about 6 to 8 ft in diameter and lined with the same masonry as you use for the retaining wall. In other words the tree would look like it is planted in a shallow hole. You see this technique employed often where it becomes necessary to raise the ground level around existing trees.
If you cover the area from the interior wall to the outer retaining wall (with bricks etc.) then you are denying the tree necessary rainwater. I would not cover this with brick.
Whether or not you can just place your retaining wall on sand on grade depends on your frost line. If you live in a relatively cold climate ( say New York and North) then you should start your footings below the frost line or frost heaves will knock the wall over after a few years.
I would recommend mortar, but this may not be necessary.
HTH,
EJ in NJ
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Thanks. However, there is not as much space as you think. The entire soiled area around the semi-circular driveway is about 18' at the widest spot, that would be like the diameter except it is actually less than half a circle. I will be replacing the wood border with a brick border. If adding more soil is a bad idea I will just leave the soil at the current level, and not stack the wall as high as originally intended.
My location is Miami, FL, so no frost to speak of, but does have frequent rain and occasionally hurricane force rain in the summer months.
MC
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