Tulip Poplar is not a tree that tolerates root disturbances well....not like willow or poplar but probably better than oak. Piling soil over the roots will likely kill or severely impair those roots. What % of the root zone will be impacted (by both regrading and compaction by machinery access? Will the regrading go right to (or around) the base of the tree?

A photo will help.

The main common issue with burying roots is it putting them farther away from the moisture that comes out of the sky, in the form of dews, fogs and rains. Although different species do vary in their tolerance of being buried as a general policy no tree that is to be kept healthy with certainty is to be subjected to a fill.

Creosoted railroad ties are ugly, malodorous and poisonous. (One landscape contractor friend calls them "tacky, tarry and toxic"). Definitely not suitable for a child's play area or similar uses, unless roofing paper is stapled onto the outside of them to form a protective barrier. And nobody picks at it or pulls it off. Even then there is still the matter of creosote leaching into the soil, unless every surface of the tie is papered before installation.

Also when in contact with the soil eventually these rot away, despite the toxic treatment, and have to be replaced. Landscape timbers treated with other materials would be expected to have similar issues, the point of the treatment always being that it protects the wood from being eaten or decomposed by making it persistently poisonous.

What percentage of the tree's roots would be buried? There is a good chance they would be suffocated...not a certainty, but a good chance. Is there a way to avoid driving heavy machinery over the root zone?

Thanks for the comments everyone. I'll get a couple pictures when I get home from work tonight and post them.

Ken_Adrian, I'm a displaced Buckeye in South Carolina :) We have clay here too, it's just red!

I would say that only the southern side of the root zone would be impacted and not the trunk. I agree with the timbers and probably will use bluestone which we have left over from a pathway for the step anyway.

One option would be to build a half circle smaller wall around the tulip poplar to keep the roots happy but considering the size of this tree I'm sure those roots are already under the existing wall anyway.

There are a couple of other trees that might be impacted but I believe they are sweet gum and it would not break my heart if they expired :) The tulip poplar would cost a fortune to remove if it were to die!!

Pictures later......

I would opt for half circle smaller wall around the tulip poplar, I dunno maybe 15 feet out from the base? Can you measure diameter breast height of the tree? (Circumference at 4.5 feet off the ground in inches, divided by 3.14), then multiply by 3 for poplar, to estimate age. Just curious how old it is. Also, keep in mind that 50% of the tree's root system won't be affected at all, since it is on the other side of the tree :)

Tree wells don't work - the roots are still buried.

"Tree wells don't work - the roots are still buried."

A 15' radius semi-circle isn't a tree well. Will what is being suggested, work?

i dont understand the pix... is your yard on the upside of the wall ...

frankly ... why not just leave it.. and let ma nature settle it any way she wants.. over the decades ... as it doesnt appear you need this space ...

it is really nice back there.. i just dont understand ... what you are FIXING????

ken

ken_adrian Adrian while it looks fine in the picture, he says the retaining wall is failing. He thinks it would be cheaper to put in a slope then replace the retaining wall. He's fixing a potential avalanche. I assume his yard is on both sides of the wall.

Failing? I've seen walls a lot worse than the one in the picture, last several decades.

Other idea would be reduce the height of the wall, slope the dirt on the high side to match top of wall, cap the wall and forget it. The reduced height will be less pressure on the wall thus extending the life of the wall many, many years.

Would a few buttresses extend the life of the wall?

A tree with a 5-ft.-thick trunk is going to have a root system that extends very much beyond a 15-ft.-wide circle - whether or not the proposed installation would fit the definition of a tree well exactly is irrelevant.

Have you talked to any professionals that deal with walls about this?

doesnt help me .. where is the tree.. behind the camera???

and i dont understand where the soil level is.. on the other side of the wall ...

it almost looks like the wall is integral to the house.. never mind the trees ...

ken

Clarification: I assumed the wall was o lay being halfway around the tree, and the dirt wouldn't extend beyond the halfway point. I didn't intend to imply fifteen feet entirely around the tree, obviously that would be stupid. Clearly I know that tree roots extend beyond 15 feet from the tree. I am not an idiot.

Brian, if it is any help, when they built my house, they graded in my driveway a few feet, burying about 50% of the closer-in part of the root system of a nearby 40 year old tulip poplar that was about fifteen feet away from the edge of the driveway. On the other side of the poplar, they built another house whose foundation covered another wedge of the tree's root system, about the same distance away. The houses were built in 1975, and here we are 40 years later and the tree is now over two feet thick at breast height, and healthy as can be. This is why I think your tree will be fine with what I suggested.

So what we are talking anout is burying almost half the tree's roots. The buried part would be buried in a lot more dirt then a typical driveway regrading process. This may or may not kill them. If it kills them, the tree may or may not be able to function with half it's roots.

Also, the other issue is how it is built. Where you park the heavy equipment maters. They could crush roots or compact soil.

Is the wall just cracked or is it bowing out or...? And is it just that one section? Instead of a complete replacement, there's no way to just repair that part of the wall?

Rodney

if the wall is not integral to the house.. why not hire a dude with a cement saw ... and cut out a section.. and put a stairway down to the natural level below ...

i can not even begin to contemplate the amount of soil you would have to move in.. to make a sloping back yard ...

ken

Ed, I would agree with you that whatever gets buried has a good likelihood of being impacted or killed. However, I would strongly disagree with you that we are talking about killing half of the tree's roots.

My opinion is that half (maybe more like a third) the tree's roots were affected/killed when the house was initially built and the yard was initially terraced.

I have read conflicting things on poplar tree roots ( I read up on them a while back since I have two 2-foot-wide-dbh poplars flanking my house.) One thing I read was a study where they looked at pole-sized poplars and found that the poplars have a lot of roots rather close to the tree, and not a bunch of radial and evenly spaced feeder roots.

I have also read that poplar roots can extend anywhere from 160 to 490 feet away from the tree.

I am assuming that the area on the other side of the tree is either forest, or backyard of another house.

My assumption based on this is that when Brian's house was built and the yard graded, the poplar was definitely affected, so it overcompensated the root loss on the upper slope by creating more feeder roots on the lower slope to get more moisture.

As an aside that I won't get too much into, and that you may already know, there is emerging research that trees are connect by a mycorrhizal fungi network via their roots, and trees can actually share and transfer nutrients. The larger trees tend to be “nodes" in these networks. Because of this tree's size, my guess is that it has a lot of ways to get nutrients.

That being said, obviously less damage is the most preferred option, and getting someone to bobcat away all if the terraced soil would probably be best. That sounds like it would be a lot of money, but maybe somebody nearby needs a lot of fill dirt for free.

I'm wondering that in your research you were looking at Poplar instead of Liriodendron? Poplar can handle all sorts of burying. I've seen them healthy with over six feet of fill. I agreed to remove one that was about a foot in diameter on a job once, figuring I could just dig it up, stump and all. I went down six ft. and never hit a root. It had been backfilled with a bulldozer several years earlier when the house was built. I cut it off a three ft. and double bagged it before filling in the hole.

Liriodendron is a whole different matter. I don't have much experience with them, but I would imagine several inches of soil in the root zone wouldn't be harmful. I've done it with a lot of other trees. Water the root zone good first, and then again after the soil has been applied. Embo has a point.

Is the wall failing out, or one end settling different than the other and not bowing out? The picture doesn't show which.