I don't know if it's the lilac impacting your retaining wall - looks like failure due to the ground heaving, shifting, and settling. Not a mason, but would think freezing and thawing (or a bad mortar mix) could cause mortar to pop. And now that it's underway, it'll continue with or without the lilac. The root system is probably fairly extensive if you're getting suckers ten feet away. If you want to get rid of it, dig around it in a circle, chopping off the roots as you go. Labor intensive, but doable. Then paint the fresh root cuts with a non-selective herbicide like RoundUp or some other stump killer type product. Or, have it it professionally taken out and the stump ground. You might still get a sucker or two, but since they'd no longer be attached to the parent, mowing over or ripping them out should take care of them. I have many, many, many feet of old and huge common lilacs -and I've never seen a sucker more than 6" from the parent plant. But I concede different varieties do different things. And I kind of welcome the close in suckering since it replenishes any old wood I might lose. There are wall and tree/shrub experts on the forum; hopefully they'll chime in.

I'd like to do this to one flowerbed I just created, but I'm running into poured concrete next to foundation of sunroom. What soil I added when I created this flowerbed has settled and then me stepping on the mulch to get to the darn thistles to dig them up hasn't helped. I was thinking of starting some type of border around that flowerbed, but will run into roots from a hugh maple tree that has been there for 35 yrs. when the area was built. There's nothing I can do to the roots of that tree. It belongs to the Mutual we live in. I was thinking of starting the back of the flowerbed with some type of pavers like you have, starting where the poured concrete from the sunroom begins, which would leave a small space between the pavers and the sunroom foundation. Can you forsee any problems I might encounter with this idea? The original owner used pressure treated landscape timbers on the side of the house where all the hydrangeas are planted. Maybe I should stick with that. Wouldn't they cost less, but I want it to look attractive and not have to worry about any termites. But buying the pressure treated landscape timbers, I shouldn't have to worry about termites, right? I could also plant flowers that would cascade over the edge of the landscape timbers to make it more attractive, right? I have a vision in my head, not to get it to work! My husband and I have put down landscape timbers before at our former home and I feel sure we can do the same here. Don't know if we have to get Mutual approval or not. Another idea was to buy the white scalloped pavers like are in front flowerbeds. Which would be less work and less expensive?

i recently built a dry stack circular stone wall around a large pin oak in my yard the wall is 32 inches at its highest point. I am worried about the roots of the oak pushing upward on the wall and destroying it, although i did do some intense labor around the areas where the roots were the most visible. I purposely postioned the rocks in these areas in such positions that there is room for the roots to grow before touching the stones........... time will tell.

Ken, thank you very much for your comments! Here is some more info; if you can add to what you've already written, I'd appreciate it. The walls are made of 12-18" natural rocks dug into the ground just a little, with no foundation since the walls aren't very high. We hadn't thought about eventual large roots moving the rocks in the walls (we've been more concerned about the gophers destroying them!), but I'm sure you're right about this. The Tanyosho is behind a long wall that faces the house (west, but there are lots of oak trees that block the afternoon sun from the wall) and meanders across the front of our lot about 20-30 feet from the street. The land slopes gradually down from the street and then back up in front of the house. This wall was put in to hold about a foot of top soil that was added to the slope so I could plant shrub and floribunda roses out front to get the morning sun. If the roots push out the wall, that would still be ok since there is plenty of space below this wall, and if it becomes a rock garden instead of a continuous wall, that could also look very pretty. The wall doesn't have to be there to hold the soil (I didn't want to spend the money), but my husband just thought it would look nicer with a wall, and it does. We know about how large the Tanyosho gets in about 25 years since we saw a couple out at Hidden Lake Gardens where my husband fell in love with the exfoliating bark. They look just like the second one on the left side of the pictures in the link you have in your post (BTW, I love the bonsai!). Since we went out there after having you recommend HL Gardens here, you probably know which trees I'm referring to! The Emperor I and Waterfall are behind a southeast facing wall in front of the house that gets filtered shade for most of the morning. In the summer, they get the most sun early to mid-afternoon. There's room below this wall for more rocks and soil to be added and to have a rock garden if the wall gets moved and destabilized by roots. This is probably what we'd have to do, since the wall is very necessary since it is holding up a lot of fill that has the paver walk above it going from the driveway/garage area to the front porch. The Emperor I was just planted last summer. I had to water it and the Waterfall (planted with the Tanyosho 2 summers ago) constantly to keep their leaves from shriveling up. Our soil is loamy sand with a few inches of top soil added on top. We don't have anyplace else we could transplant them to since there's not enough sun elsewhere on the lot, so I was just trying to figure out if they all are likely to survive over the long run. I also remembered how clearly defined the root layer was when they dug for the foundation of the house--everything below about 6" was sand, with no roots or other organic matter. So I was trying to envision where the roots of these 3 trees would grow--down for a foot or two to get to the next layer of soil at the base of the walls where there would be moisture? I didn't know if they could live under these circumstances. I'm not as worried about the Tanyosho, since we were told to water it sparingly, if at all. Anne