We see them all over the valley. Dooley walls with big stair-step cracks from top to bottom because of tree roots. Fixing them, unfortunately isn't so simple...
As a masonry contractor who offers satisfaction guarantees on my work, I typically shy away from doing fence block repairs unless the homeowner agrees to let me do the repair fully.
When I say fully, I mean so that it will last, without cracking again as the tree roots continue growing, for many years. This will require a lot more work than just patching the crack and a lot more work than just taking the wall down to it's footing and rebuilding it.
Most of the time, the tree root is under the footing. So it's lifting the wall by lifting the footing. As well, there's usually more than just one root to contend with. Until we deal with the root cause, no pun intended.
To fix this problem permanently, which is the only way a responsible contractor should do it, that root or roots must be cut back. And then a barrier must be put in place that goes significantly deeper than the tree roots. So any new root growth comes up against the barrier and just turns around, rather than going under. It's got to be too far and fruitless, aka waterless, to encourage going under.
My prescription typically is remove the cracked and leaning sections of old wall. Remove the whole section of footing that has been heaved up. Saw it up and jackhammer it out. Then dig deep and pour a deep footing. A deep, deep footing. Go down two feet or more from the bottom of the offending root(s). Then rebuild the wall, as before.
An alternative to the deep footing method is the remove the whole tree method.
Does this sound expensive to you? It's going to definitely cost more than that original section of block fence cost. But if that wall falls on your child or your neighbor's child, that repair estimate will sound like an amazing bargain in hindsight.
There are many contractors that will cosmetically repair the heaved block panel. They'll take down the wall to the lifted footing, cut the first course accordingly to accommodate for the higher footing, and lay up the wall. It will look the same as the repair done the right way.
If you agree with doing things right, give Mesa Masonry LLC a call. We will do it right.