It is far more likely that you harmed the tree by applying the 4-5" of soil around it in the first place. The bulk of a tree's roots, especially the smaller feeder roots that provide the bulk of the tree's nutrient and water access and gas exchange, are located just beneath the soil surface and layering on extra soil can effectively starve the tree of oxygen, eventually killing it.

How much damage might have been caused depends on how extensive this layer of added soil is. A large, well-established tree will have a very wide spreading root system so a narrow added soil tree ring - maybe 36" deep - may not have a long lasting effect but it is typically cautioned to never change the grade or soil elevation anywhere within the dripline. Damage that is created by such an elevation change may take anywhere from 5-10 years before it is noticeable and the tree starts to decline.

So yes, get rid of the excess soil ASAP, mulch the area lightly and hope for the best.

Ditto gardengal's information, but I have a bit of a qualifier that comes from experience having done this myself.

While some trees are indeed sensitive to having some of their roots covered, and all trees would probably be sensitive to having all of their roots suddenly covered, a lot of these big trees are tough survivors who will shrug off a little insult to a portion of their roots by growing more where conditions are better.

And in terms of root growth, the trees I've had experience with are flagrant opportunists. Every time I have tried to make a flower bed near a big tree, the new soil has been infiltrated by tree roots, usually a mass of them, within two years, with the result that any plants I put in that bed are outcompeted for moisture and nutrients by the tree, and never thrive.

So while you may be right that the myrtle didn't take off because they soil stays dry, I'm going to guess that another reason might be that it could not get established as fast as the tree was able to send rootlets into the new soil.

All this to say that when you scrape away that soil, you will likely be disturbing roots yet again. So if you value the tree, you might remove the soil gently, just raking it away, and maybe not fixate on returning to right to the original soil level but more on smoothing things out. Remember that a tree naturally mulches itself with leaves or needles, so soil level does not necessarily stay constant.

I'm assuming you didn't bury a portion of the trunk, but if you did, that should also be gently re-exposed to the extent that seems possible.

KarinL

I completely agree with Karin and GG. You have received very good advice.

The way I think about it is that usually the canopy of the tree gives you an indication of the extent of its root spread. Then you can consider the percentage of the root area the has been effected. In my experience, most well established trees will not be effected by a less than 50% intrusion of their root area; I mean in terms of adding planting areas, not excavating a driveway or something like that.

About 6 yrs ago I had a client who wanted to create a Japanese style garden in a shaded woodland setting of about an acre. For each and every tree we calculated the intrusion of the additional planting areas on its root area. We kept it to 50% or less and there has been no tree damage or loss.

I would gently remove the myrtle and dirt following Karins excellent advice. I would be cautious however about replanting the myrtle after you tamper with its roots again - I think the combination of removing the soil and then digging among the roots might be too much. Also during the 6-7 years that the soil has been there the tree roots probably have grown into the tree circle quite a bit. I think using a hose to wash away the soil would be the least invasive way to accomplish what you would like to do.

All...Thank you for your comments. In retrospect...what I did was stupid. I suspect that if I planted the myrtle at ground level...it would have taken off better.

I have posted a picture of the tree ring at the URL listed below. The tree is a very mature Red Maple. The size of the ring is oblong approximately 4' x 3' oval....so I feel I did not invade the dripline of the tree.

Since I am in Pennsylvania...do you think removing the ring in late March is too early? Or do you have any thoughts as to when the earliest I can remove it safely?

Again...thank you for your comments.

Here is a link that might be useful: Tree Ring Photo

FYI, the dripline is that area from the trunk outward to the perimeter of the canopy. So yes, your tree ring is within the dripline.

You can remove it at any time you can work the soil (not frozen).