bed around tree - will it damage the tree?

15 years ago

Hi,

I have contracted to have my front yard landscaped. They have not

started work yet, being busy on other projects, but now I am having

some serious reservations about the design, and I wonder if I should

change it before they start.

The issue is the tree in the front yard. It is a pin oak, probably

about 20 years old. It is a nice healthy tree; I don't know how tall

it is but it is about 18 inches in diameter.

The proposed design includes a lozenge-shaped bed around the tree,

about 24 feet long and 14 feet in diameter, kind of like a berm with

the tree on one side.

The edging for the design is stone blocks. I want this edging as it

will match all the other beds in the yard But to put this edging in,

they have to dig a trench around the tree. The trench will be maybe

8" deep? They put in a bed of gravel and then concrete the blocks

in. At any rate, installing it will involve cutting some of the

surface roots all the way around the tree.

I'm worried that trenching around the tree will damage it. I would be

really upset to lose this tree; I lost both my back yard trees

(maples), one to ice and another to wind, so this is the only large

tree on the lot. And it has had a bit of a rough year so far; a big

wind storm blew off many of its new leaf clusters, and it is only now

getting around to replacing them.

The landscape designer said it would not significantly damage the

tree, as the tree roots go as deep into the soil as the height of the

tree.

I think these landscapers are good. They did my back yard last year

and they did a nice job; they are certainly not the cheapest option.

So I think they know what they are talking about, generally speaking.

Still, I have reservations - after all, ultimately, I'm the only one

who really cares about the fate of this tree.

So, my question - would trenching around this tree damage it

significantly?

Thanks!

Featured Answer

gardengal48 (PNW Z8/9)

15 years ago

Adding more than about 2" of soil to the area surrounding a tree is sufficient to kill it. You may not notice the damage immediately.....it takes time for the roots to die off. But eventually it can, and usually does, happen. If it is a relatively small area, the damage is not as likely as tree roots extend far beyond the dripline or canopy edge of the tree. 24'x14' is a good sized area.....I wouldn't raise the soil level uniformly all around the tree in this area but you can get away with a small berm off to one side

I would have some reservations about the trenching and the possible damage it could do to the roots. Contrary to what your landscaper told you, tree roots tend not to go very deep (with the possible exception of a tap root and most trees that produce these - a distinct minority - grow out of them with age). The majority of a tree's roots are contained within the top 18-24" of the soil, with the very fine and extremely important feeder roots located just below the soil's surface. They certainly do not go down a distance equivalent to the height of the tree!!

An established tree can lose about a third of its roots before it starts causing issues but ideally, you do not want to sever or cut anything larger than 1" in diameter. Oaks tend to produce surface roots depending on species, so there is a good likelihood some larger roots will be damaged.

I'd advise against it :-) It is just not worth the possible risk to the tree for a minor aesthetic consideration. But you could do a bed without defined, trenched edges, provided the soil level issues are considered.

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Comments (6)

duluthinbloomz4
15 years ago
Well, if you go ahead with this landscape designer's trench, any damage to your pinoak would manifest itself at the crown of the tree... cut the roots and you might eventually see dieback in the top.

Pinoaks are shallow and fibrous rooted. Saw some calculations on cutting roots close to trees somewhere - any serious root cutting should be three times farther away than the diameter of the tree at chest height... 18" diameter x 3 = at least 54 inches away from the base of your tree.

While everyone is busy with other things, can you work at reconfiguring the bed a bit to give the tree wider berth?
natal
15 years ago
If it were me I wouldn't take a chance. I understand you want to use the same stone, but at what eventual cost? I'd be working on a re-design.
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missingtheobvious
15 years ago
You compare this bed to a berm -- are you raising the soil inside the edging, and if so, by how much? Raising the soil around a tree can be bad for the tree's general health if too much of the area under the canopy is suddenly buried too deep (ask at the Trees forum how much added soil is too deep for a pin oak). Raising the soil around the trunk can result in disease or bug damage to the bark; either one may be enough to kill the tree, but if the bed is only slightly higher than the original soil level, one possibility is to raise the soil at the edges of the bed and slope it down toward the tree so the soil level at the trunk doesn't change .

To find the tree's height, enter your height, the length of your shadow, and the length of the tree's shadow:
http://www.csgnetwork.com/treeheightcalc.html
aloha2009
15 years ago
I have a simliar dilemna to you.

We have a notoriously shallow rooted maple. We changing EVERYTHING around it. We read that even though, a tree may not initially show the stress, it will eventually and it's lifespan will be shortened.

We chose to remove the grass around it by spading it out instead of using RU where we did it in other areas. We also needed to put in a pathway. For something like concrete or stone, we'd need to dig down like you are doing and put in a base. We've chosen to put in a breeze walkway and work around a huge root.

Once you find out the tree has been compromised, your landscaper is going to be out of the picture. There are many ways you can beautify and area. I'd play it safe.
quasi-starfish
Original Author
15 years ago
Thanks for the advice. I ended up changing the design and running a bed down the edge of the driveway rather than around the tree. Both I and the landscape designer think that the new design is better than than the original, so everybody (including the tree) is happy.