Retaining walls around trees - too much soil compaction?

daniel_clAugust 31, 2010

In our community there are lot of yard trees with a ring of low, decorative retaining walls (about 5' in diameter) surrounding the trunk. Most of them look neat and beautiful.

We just planted a magnolia leonard messel (currently 5 feet, ultimately 15-20 feet) with the same retaining wall setup. We lay just one level of bricks directly on the sod (using a little fine gravels for leveling). The tree is planted on the same soil level outside the ring.

We are concerned only that whether this 5' ring of retaining wall (with occasional foot traffic on it) would severely compact the soil surrounding the tree and prevent the roots from growing out of the ring. Shall we remove the ring in a few years for the magnolia's soft root to reach out?

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karinl(BC Z8)

Tree rings are widely derided in landscape design circles (I think the Renegade Gardener does a send-up) but embraced by many ordinary people whose objective is to make their yard look nice as opposed to achieving a certain design standard for the big picture. I have to say that my reaction to them varies, in that there are some very ridiculous looking exemplars, others where I have to drop my snobbery and also say, gosh, that's pretty.

And I mean, it isn't always obvious what else you can do to make a tree grow attractively out of a lawn, independent of whether the tree is well chosen for the site or well placed on the lot - either you can't mow right up to the trunk so you have unmowed grass and weeds, or the roots/tree debris cause an uneven and sickly bare patch under the canopy. So yes, the rings often do look neat and beautiful.

I think your circle will be fine for the tree.

I doubt the amount of foot traffic you describe will affect the tree. I suspect too that the roots will grow further down into the ground than the one layer of brick, and if they do encounter that obstacle, they will grow under it (if you have plastic or landscape fabric, which you should not have, the roots will stay closer to the surface in a desperate quest for water, and will lift the brick - this may happen anyway if it is a very surface-rooted tree). Mostly, your roots will go down far enough to be undisturbed, and a five foot circle certainly gives the tree enough room to compensate a bit for any excess trampling that does occur outside the circle.

Just keep an eye on your tree and see if it looks happy and healthy. Trees have ways of letting you know if the conditions aren't right - you just have to train yourself to recognize what they are telling you.


    Bookmark   September 1, 2010 at 6:55PM
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toronado3800 Zone 6 StLouis(6)

If i am understanding right then i agree you are fine.

Tree ring flower gardens bother trees in two ways:
one is when the garden is created after the tree has been planted. This frequently ends up with dirt piled on top of the pre.existing rootball and a tree which was planted at the right depth is suddenly a foot too deep. Also folks will come by with a tiller amd till up the tree's roots when killing the grass for the bed.

Second the bed can create an isolated area in the yard which the roots cant grow out of and either holds or drains water too well.

I dont think you have done either. Just plant some perennials or limit your soil excavation when planting them impations every year:-)

    Bookmark   September 4, 2010 at 12:24AM
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Thanks for the information and assurance. The magnolia has been "happy" since its installation in late June. No signs of stress.

Here is a photo of our setup. I hope it does not fall into the ugly tree ring category.

We filled the spare space with a few small plants. Once the magnolia's shade covers them and its roots grow beneath them, we will give back the space to the magnolia.

    Bookmark   September 4, 2010 at 9:31PM
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Embothrium(USDA 8 Sunset 5 WA)

You're the one that has to look at it, whether it's ugly or not is up to you.

Definitely do not do anything that involves digging among the roots of the magnolia. The ideal situation for the tree's well being would be a mulched bed or groundcover planting extending out far enough from the tree's branches to protect its rooting area.

    Bookmark   September 6, 2010 at 11:04PM
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My neighbors are planting several magnolia trees next to our retaining wall attached to our house. Will the roots damage our wall?

    Bookmark   August 5, 2011 at 7:53PM
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missingtheobvious(Blue Ridge 7a)

jim, your question will get more attention in a thread of its own, particularly since your question is different from the thread title.

It would help to know:

= how far the magnolia trees are from your wall;

= how high the wall is;

= what the wall is made of;

= whether the soil behind the wall is higher next to your house or toward the neighbor's property;

= whether the wall runs parallel to the property line or is in some other location;

= how close the trees will be to the property line;

= what variety of magnolia is being planted.

    Bookmark   August 5, 2011 at 9:37PM
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toronado3800 Zone 6 StLouis(6)

Jim there is a TREE forum where myself and some folks who do quite a bit of research on the subject angrily deride Bradford Pears and give advice on this type of thing.

Oh, and Obvious has a great list of questions.

    Bookmark   August 5, 2011 at 11:05PM
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Adding a decorative hardscape around a tree does look nice but also is hard on a tree. I wouldn't consider doing something like that until the tree is established and had some time to let its roots run a bit. There are other options besides using heavy stones or other heavy materials as well, we had a create a new but worn looking circular wall around the base of the tree but they used a composite other than stone that was much lighter and will but less pressure on the tree's roots.

Here is a link that might be useful: retaining walls for trees

    Bookmark   September 6, 2011 at 6:15PM
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