Retaining wall around a tree.

davidivad

Hi, I'm considering building a retaining wall as a feature like this in my garden. I would then plant a tree inside it. The wall will be 800mm high, would block on edge be sufficient here? Block on flat would be better, but far harder to achieve the curve, I think block on edge would suffice, am I correct?
I would then clad it later with fancy stone cladding.

10-10-20

Hi, the thickness of the wall is one part of the problem as well as the curve. I don't think that it's going to hold tree growth when on flats. Your best bet is a block designed for retaining use, such as these and similar interlocking ones:

https://mavink.com/explore/Retaining-Wall-Blocks

As you'll see in their specs they have a minimum radius, but you might find that they work for your objective.

ted1

I’d look at using something like this below and building the wall around it

https://www.murdockbuildersmerchants.ie/concrete-manhole-ring-1200-dstep

https://www.boards.ie/discussion/2058384008/retaining-wall-around-a-tree

Lumen

I know it's only an example, but the pic you've provided looks bad to me.

Two issues:

1. The spread of the shrub is greater than the diameter of the soil, so the shrub will suffer from root restriction. It might just grow more slowly, or it might drop leaves particularly during hot weather, or it might die.
2. Because it's effectively a raised bed, the soil will be warmer in the summer and colder in the winter. This will make the root restriction worse, as warmer soil dries out faster.

I don't know when that pic was taken but the leaves do appear to be dropping.

davidivad

Some great ideas there lads. The retaining wall blocks seem ideal.

GreeBo

https://www.boards.ie/discussion/comment/122947480#Comment_122947480

I wouldn't build anything until you have picked your tree/shrub and confirmed that its rooting requirements will be met by the size/height of your "raised bed". Some will send down a tap root and might be able to handle it, others are wide an shallow and might either die or knock the wall down :)

You might be able to "fake" it by having the ground level as normal or close to it inside the wall, plant the tree/shrub as normal, then backfill with stone or something well draining, while protecting the truck.

The tree/shrub will grow as normal since its just in the ground as normal, and you built a wall around it. Depending on the height of the think you plant, this should work out just fine tbh.

standardg60

https://www.boards.ie/discussion/comment/122945981#Comment_122945981

As long as the base of the raised bed is open to the ground underneath neither point would be an issue as most trees will root down once they reach the perimeter. As Greebo pointed out above the main issue would be the tree roots knocking down the wall if they're inclined to grow horizontally. That would rule out Cherry for one.

What is the OP planning to plant?

davidivad

https://www.boards.ie/discussion/comment/122950579#Comment_122950579

I'm planning to plant a japenese maple. Shallow roots i think.

standardg60

https://www.boards.ie/discussion/comment/122950655#Comment_122950655

Absolutely no issues with those, plant away.

Lumen

https://www.boards.ie/discussion/comment/122950579#Comment_122950579

Interesting, thanks for the correction.

I (had) built a retaining wall around an existing tree this year and despite being careful to give it space, I still got crazy leaf drop about two months early. Hopefully it will recover next year.

But I guess established trees are a different problem than a new planting.

I still think the example pic posted looks incredibly restricted, and also looks like a transplant. I can't see how you'd get that thick trunk unless it was hard pruned from a larger canopy.

I have some old potted bay laurels and the trunks are about an inch thick.

CelticRambler

https://www.boards.ie/discussion/comment/122951433#Comment_122951433

I (had) built a retaining wall around an existing tree this year and despite being careful to give it space, I still got crazy leaf drop about two months early.

You can't, as a rule, enclose an existing tree and increase the depth of soil upwards without causing problems. Even a nominally deep-rooted tree will have small roots that need to be close to the surface. If you built a wall around the trunk and straight away heaped a metre of soil on top of the original surface level, that'd have negative consequences. The better/safer way to bury a trunk is to do it at a rate of about 10-15cm per year.

Calahonda52

https://www.boards.ie/discussion/comment/122951469#Comment_122951469

What's not clear from the OP is if the raised bed is built first and then plant the tree or plant the tree and then build the raised bed.

If the latter it could be sleeved in say 12" duct[ or whatever the max diameter of the trunk will be and the raised bed then would not impact the trunk and no root pressure on the wall.

Maybe😎

Lumen

https://www.boards.ie/discussion/comment/122951469#Comment_122951469

Sure, I haven't changed the soil level, I just cut and retained one side at the the canopy limit where I've put in terracing.