Growing Mangrove-Like Tree Roots in a Soil Wall - Western Washington Zone 8A

I live in Western Washington (zone 8A) and I need to block sound along the edge of my property. It seems like mass is the solution.

Some people use earth mounds to accomplish this but due to the height necessary (for my case 6ft) the base needs to flare out. Basically making a triangle through its cross-section. This requires both a lot more space and a lot more earth works.

It might be silly, but I was thinking maybe I could make a 6ft tall but only 1ft (or similar) wide wall of earth, basically just a rectangle through its cross-section. This could would be held in place on both sides with a wooden/burlap structure that would decompose in place over the years. But the long term solution for securing this earth would be planting trees or other woody plants along the top (and eventually its sides).

My hope is that the trees could grow long mangrove-like roots through the wall and ground, both adding strength and mass to the wall and securing its soil.

Is that a crazy idea? If not, are there any tree species for my area that you'd recommend for this type of project? Any tips?

I imagine the wall would easily dry out so I plan on running irrigation along the top until the trees have enough roots into the ground, while not over watering to prevent erosion.

Western hemlocks love to get their start on top of a nurse stump or nurse log. The baby tree sends roots down the side of the stump. The stump slowly rots away leaving the new tree up in the air. It is stunning to see these out in nature. I'll see if I can add some pictures.

Ecology Picture of the Week shows several examples: EPOW



Normal mangrove roots occur where there is a high water table. Western redcedar are tolerant of that environment, so you will see them doing that next to streams and lakes.

So maybe you would build up a dead hedge, focusing on any big stumps or logs that you can find, and then plant some Western hemlocks on top of them.

Arborvitaes make a great sound barrier.



https://permies.com/t/211931/Arborvitae-Pruning

What you are describing reminds me of Espalier Training:



https://permies.com/t/69091/Espalier-Training-Graft-Living-Trees

Another idea is to make a series of hugelculture beds the height you are suggesting and plant trees at the top:



https://permies.com/t/get-started-hugelkultur-beds

This is also a idea:



https://permies.com/t/25097/Hugelkultur-feedback

https://permies.com/t/50120/Tricks-Dirt-Sliding-Hugel

Here is also a similar thread that you of other might find interesting:

https://permies.com/t/84877/Noise-Barrier-Ideas

That's awesome, thank you so much!

I'm wondering if that would maybe even allow me to fully skip 99% of the earthworks?

Maybe I could get started by placing something like the tall cardboard tubes intended for concrete forms, secured with 2x4s for bracing, fill with soil, and plant Western hemlocks at the top. Over time I could bring the dead branches from the property to fill in the gaps between the trees and slowly add stuff for infill, all of which wouldn't need as wide of a base given the strong posts formed by the semi-established trees.