Suppose you have a tree growing about six inches from a wall with a brick or stone foundation. How big does the tree have to get before its roots start to hurt the wall?
I think it really depends on the tree and it’s root system. I saw a horror story on TLC or Discovery about a couple that had a certain type of tree root invade their foundation. Even though they only saw a few surface cracks, the foundation was totally destroyed and the house had to be completely rebuilt.
The root system is typically as large as the foliage. However it depends on the type of tree it is. Call a tree service in your area for advice. They will advise you as to the potential for damage and what options are available for you. The sooner the better as roots can easily crack a foundation.
The problem is, that by the time you see any signs the damage is likely to be very severe. If it were me, I’d transplant, if it’s small enough, or just cut it out.
Well, we’ve already cut most of the trees down. They were volunteer locusts, not very big–trunk diameter only a few inches. We haven’t noticed any ill effects.
On a purely hypothetical note, what about espaliered fruit trees? Those are often grown against walls.