bed around tree - will it damage the tree?

12 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)

12 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.