Tree Roots

junk1958

Hello -

First post, looking forward to hearing from you with your many years of experience.

A friend has a backyard concrete patio, probably 15 ft deep, running the width of the house (40 ft?). He also has two trees, one at each of the two far corners of the patio (that is, away from the house.)

The trees are probably 10-15 ft tall. I have no idea of the type of tree (they are both the same kind of tree) and cannot get a picture, but they are probably both around 15-20 yrs old, about the same time as the back yard was landscaped, probably when the house was built. I know they are leafy trees, not pine or palms, but I think they keep their leaves pretty much year around.

Now the concrete in the patio near the house is starting to crack, and he believes the roots are causing the cracks even though the cracks are quite a distance (10-12 ft) from the base of the trees. However, the concrete nearest to the trees is not cracking.

I asked if the cracks could be earth quake damage, since we do live in So. California, but he said no and he is certain it is the roots of the trees.

So he is planning to have the tree roots pruned on the side of each tree that is facing towards the house and then wants to put some concrete in the ground to some depth to force the roots to go elsewhere, away from the patio.

He likes the trees and would like to keep them, but I do worry that pruning the roots is going to permanently damage or even kill the trees. I also wonder how likely this plan is to keep the roots from the patio unless the concrete goes quite deep - say 5 - 10 ft.

One of the trees is 1 or 2 feet away from one of the far corners of the patio. The other tree is 4 or 5 ft away from the other far corner.

What are your thoughts? Any suggestions of how to tackle this problem.

Thanks!

Eric Frei

Good chance the trees will dieback or even blow over as he is cutting within the SRZ.

AS4970 Draft| Australian Development Tree Protection

How roots navigate around obstacles in the soil

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junk1958

Thank you kindly for your comments. I will discuss it with him.

Also, thanks for the links to the other two threads. Very interesting. I was reading the second thread and began thinking that it would be great if someone, somewhere would do a scientific study on the force exerted by roots, and then came the reference to the journal article!

Would be interesting in clarifying if you or anyone else has any suggestions on what else to do other than cutting down the trees since pruning the roots doesn't seem to be an option based on the info supplied.

By the way, the trees are not large in diameter - maybe 12 inches or so. But they do have very large, thick roots, even at the surface. I remember noticing he had already tried to cut through at least one of the roots.

Thanks again

Eric Frei

I often mention 145psi pressure exerted by tree roots.

Palm root? I'm guessing but I think not much more than 20psi (if that). Palms struggle to break or even distort a plastic pot, they may grow roots out of the pot drain holes and never tear those holes.

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Brent Ferris

Pics would help a lot. But tree roots have trouble growing under concrete unless they can get a supply of water. So rather then destabilize the trees by cutting the roots, or digging deep holes, why not find out where the water is coming from. The soil type can also make a difference. And while your friend is convinced tree roots are causing the problem because he can see the trees and it follows (he thinks) the roots are guilty, the cracks might be happening because of uneven settling under the slab, and without enough support, the concrete can crack.
More investigating is needed before drastic action is undertaken. After all, suppose you cut the roots, or remove the trees, and the concrete still cracks more. Now you will have lost the trees and be further behind, Where is the sense in that?

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derwoodii

Concrete slabs can often encourage tree roots to prosper below them. If the sub base rock support grade is a porous medium, roots can travel happily between the two profiles. Air held moisture condenses out in this layer as thermal mass concrete cools over night and so during the day this zone is kept a nice productive growth area. Tree roots elongate and expand here and cracking can happen, its not always by force exerted by the roots but by the fulcrum effect of the roots suspending areas of heavy concrete off the sub base (snap) that is as said; poorly consolidated material.

The competing interests here means concrete cracks and trees suffer unless you can without too much harm sever the innocent roots.
Perhaps try some copper sulfate in the cracks, may discourage further root growth and not kill the trees http://www.eco-nomic.com/pix/Tree%20Root%20Control.pdf

Then if he can sacrifice small sections of the big patio by removing some concrete near to trees, he may be able to cut further away from the SRZ roots and find the balance of both tree and concrete.