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Raising ground level around trees

mkr

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Aug 12, 2021
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We will be building a house and have to remove some sand and dirt from underneath the house. We were thinking of using this material on site instead of hauling it away. A corner of our lot is lower than the rest and the initial thought was to raise the ground level there. There´s also a deep and wide ditch on the edge of our lot, which could be made narrower. The ditch could take in a large amount, so that´s useful.

However, there´s two big trees on the edge of the ditch in the low corner. (See the attachment.) In the foreground is a Birch, in the back a Pine. This is in Finland, so I guess: Betula pendula and Pinus sylvestris. The ground is moderately sloping towards the ditch and the slope in the ditch right next to the trees is quite severe. Depth of the ditch is more than a meter.

The questions are:
1. How much can the ground level be raised for these trees to remain healthy?
2. How much can you fill the ditch?
3. If the trees can´t handle it, how large of an area would need to be kept intact for them?

I suppose we could remove these trees and plant new ones, but I´d rather save these!
Thanks in advance! :) trees.JPG
 
old CB

old CB

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Most trees suffer if their root flair--the widening at base of tree evident in your photo--is not above ground. The above ground portion of the tree is meant to be above ground.

That said, some trees can withstand the injury. I have several Ponderosa Pines thriving in my yard despite having sandy soil heaped up around them when the grade was changed to build the house over 40 yrs ago. But most trees do not do well under those conditions, and I suspect what kind of soil (sand vs. clay) and annual rainfall influences that. I live in very dry country.

Hard to comment on your situation without knowing more about your situation. I suggest you find a knowledgeable party in your area to advise you. Perhaps a nursery operator and/or an experienced excavating professional could tell you more.
 
Bango Skank

Bango Skank

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I’d like to see more pics of your birch if possible. I’m probably gonna look foolish when it turns out I’m wrong (again), but it looks like cherry to me.

You thinking about putting a culvert in the ditch, then filling it in?
 
old CB

old CB

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I'm not familiar with Finland, but I think you're in wet country. So another aspect to consider is how your drainage might be affected by adding fill to an area that normally drains well. Sand tends to pass water through (drain) well, so maybe it's no big thing.

But in general, messing with nature's design can be a tricky matter.
 
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mkr

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Aug 12, 2021
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Finland
I’d like to see more pics of your birch if possible. I’m probably gonna look foolish when it turns out I’m wrong (again), but it looks like cherry to me.

You thinking about putting a culvert in the ditch, then filling it in?
It´s definitely not a cherry! Silver birch is the right answer, it´s one of our most common wild trees.

Culvert is an option. Both our neighbors have done that, without permission I might add, and since we have asked for a permission, we might not get one unless it´s simply on the grounds of equal opportunity. We should get a permit to make the ditch narrower though and maybe that would be our preferred option anyway...
 

mkr

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Joined
Aug 12, 2021
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Location
Finland
Most trees suffer if their root flair--the widening at base of tree evident in your photo--is not above ground. The above ground portion of the tree is meant to be above ground.

That said, some trees can withstand the injury. I have several Ponderosa Pines thriving in my yard despite having sandy soil heaped up around them when the grade was changed to build the house over 40 yrs ago. But most trees do not do well under those conditions, and I suspect what kind of soil (sand vs. clay) and annual rainfall influences that. I live in very dry country.

Hard to comment on your situation without knowing more about your situation. I suggest you find a knowledgeable party in your area to advise you. Perhaps a nursery operator and/or an experienced excavating professional could tell you more.
Yeah, that makes sense. The question for me though is how much abuse can these trees take. How much soil was heaped up?
I'm not familiar with Finland, but I think you're in wet country. So another aspect to consider is how your drainage might be affected by adding fill to an area that normally drains well. Sand tends to pass water through (drain) well, so maybe it's no big thing.

But in general, messing with nature's design can be a tricky matter.
We apparently have 655mm of rainfall per year in Helsinki, Finland, so I don´t think it´s so wet. Our spring and early summer are pretty dry, late summer to autumn pretty wet, in the winter the ground is frozen.

Here´s the scenarios I´m considering:
1. Raise ground level X inches around the tree. How would a tree do? What would be a max X value that wouldn´t cause the tree to suffer too much? I´d imagine 1 inch would be insignificant and 20 inches maybe lethal...
2. Fill in the ditch. Let´s imagine it´s fully filled. How would the tree do with some, but not all, of the roots buried deep?
3. Leave the ground level untouched for X feet around the trees, then raise it significantly. There would be a lower level and higher level. What would happen now? What would be the min X value to keep the trees happy?

Do you have an opinion? Bad idea. good idea, don´t know?

Does anyone have any suggestions on literature on how the trees work? :D
 

mkr

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Aug 12, 2021
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Here´s the scenarios I´m considering:
1. Raise ground level X inches around the tree. How would a tree do? What would be a max X value that wouldn´t cause the tree to suffer too much? I´d imagine 1 inch would be insignificant and 20 inches maybe lethal...
2. Fill in the ditch. Let´s imagine it´s fully filled. How would the tree do with some, but not all, of the roots buried deep?
3. Leave the ground level untouched for X feet around the trees, then raise it significantly. There would be a lower level and higher level. What would happen now? What would be the min X value to keep the trees happy?

Do you have an opinion? Bad idea. good idea, don´t know?

Does anyone have any suggestions on literature on how the trees work? :D
Okay, I´m replying to myself. I was previously trying to google this in Finnish and couldn´t find anything. That was pretty stupid of me. In an English search I quickly found this: https://www.bartlett.com/resources/preventing-damage-to-trees-from-grade-changes.pdf

In summary: you need to protect the area within the dripline as much as possible or else build a system to improve drainage and oxygenation of the old soil level.

Still a question remains: If I fill in on the ditch side, how much will the trees suffer? Will it die on one side and thrive on the other side? ;)
 
old CB

old CB

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Yeah, your annual rainfall is not excessive.

But every question you pose should be answered by someone who understands your local ecosystem. An outsider can make a good suggestion, only to find that something specific to your area makes it a foolish notion. Seek people in the arborist community, or the university outreach (we have such a thing here in each county), or a tree nursery worker. Professional excavators, if they're experienced and worth their salt, often have a very good idea about what you can do to the ground and what you should not.

You seem to have a basic understanding of the situation: a little disturbance will be tolerated, while 20 inches of heaped up soil might not. And one tree species will respond well while another might not. The Bartlett link gives very good counsel.
 
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