Information dirt and roots

[hangxanh]

Seriously, has all the hype about killing trees by covering the roots with more soil and mulch been overkill (pardon the pun)? We have some mature, very tall Douglas fir in our yard. Some trees over the years have died and fallen. Some erosion of soil and time has exposed some roots. But roots run very deep and very wide. Nearby to the area we want to berm, we have a flower bed around a giant western cedar. There are masses of fine roots all over, and every year we haul in more compost and topsoil (just a few inches) for the beds. The tree roots very quickly grow through it.

Can building a berm that is about 3' to 4' wide and 1' to 3' high (low end to high end) that curves through some of the Douglas Fir trees (not up against them or surrounding them like a moat - rather snaking through them) seriously kill the trees? Really?

I am being old by one arborist I will kill the trees for sure. Another is saying they should be o.k. And God help the fool (like me) trying to find non-hearsay, validated, and practical information on the internet!! I even got conflicting information from the county extension office. SO FRUSTRATED!!

Seriously, the trunks of these trees range from 9" to 18" diameters, they are 40' or more in height. Our climate is very rainy (north of Seattle). Soil is acidic, clay and rock. The total length of the berm we want to make would be about 25' long. We would plant shade tolerant shrubs and ferns on it, and cover with layer of wood chips. A few well placed two-man rocks. A wood chip path would follow the curve of the berm around one side of the berm for light and occasional (family) traffic. We have dogs and grandkids that would love to run up and down it, too, we are sure.

The reason for the berm is to create a better growing area for some appropriate plants, to cover a mass and mess of roots, rocks, and uneven walking area, and to improve aesthetic appeal.

Please: would like to hear from an arborist with experience building berms around mature trees.

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[derwoodii]

roots need air o2 if they can't breath due to over fill the tree can suffer, the factors for this are complex eg soil type depth species compaction

site pictures will help us pls

 

[sb47]

The general rule is 1-2" per year that can be added to build up the soil around a established tree.
But there are many factors to consider.
I drove a big john tree transplanter for over 25 years and I have planted thousands of trees.
I have also seen countless trees in new subdivisions die because of back filling on the lots.
They will generally hang on for a few years but most will die several years later.
Some will try only putting soil on one side thinking the other side will keep it alive.
The roots on the right side feed and water the right side of the tree.
So by putting soil on one side will stress that side of the tree.
It all depends on the tree, and where it is growing and the soil it grows in.
If you have to put soil on the root ball, make sure it's mostly sandy soil.
Sandy soil will drain and breath better then a heavy clay soil.
Mulch tends to retain a lot of moisture, and could create root rot if it cant drain properly.

 

[cus_deluxe]

well said sb, most people dont get that the vast majority of nutrient and water uptake by trees happens by feeder roots in the top 6-8" of soil, depending on soil type. Also, roots of trees grown in the open will spread farther beyond their dripline than the roots of trees grown with more competition. it sounds to me that building a berm of the type you are describing will generally cover a pretty small percentage of the footprint of the tree. Normally i would say go for it, but clay/rocky soil in a rainy climate does NOT promote healthy root growth to begin with, and adding more stress to the roots could backfire bigtime. I have a degree in soil science from MSU so not talking out of my arse either.