That would be an excellent way to kill your trees. DO NOT BURY SURFACE ROOTS. They're roots, not your knickers. The tree really doesn't mind -- and in fact probably prefers -- that they're exposed.

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

If you're wanting to leave the stump, you could plant around it such that the surrounding plants mound over and "smother" the stump, covering it entirely. Since this is at the back of the lot and would be viewed from a distance, this would not be difficult to do. You couldn't build decent masonry work too close to the stump, but you could pull it back away from the stump, ending the retaining walls a few feet from it, and rebuild them in such a way as to look like wall ends. This means they would terminate in some pier-like way (as if they were a little chimney that is filled solid and stood 3" or so above the wall.) 3' depth of planting space within the retained area is pinched, and not large enough for the plants typically called "trees." But you could plant tall shrubs and grow them in the tree form so as to get screening above the fence. An example would be beauty bush. Not sure what the best plant for you to use where you are, but if you look around you can find large shrubs that are bare at the bottom and not too many trunks so would make candidates for tree form.

Hopefully, you can apply the general concepts to the specific conditions, as I'm not privy to where the lot lines are, and I can't see some things. Maybe that's a neighbor's white fence that is the backdrop...? And the evergreens that have been installed in front of it are yours? I think it mainly looks like a hiking trail because instead of it being a lush, green, well defined border to your yard, it's a dry, barren swath of brown mulch that has no definitive edge or shape. The part of your plan -- "and have a raised bed for bushes and such" -- I'm in total agreement with. I just can't see that the retaining wall, and the expense of it, helps. I think you need to do the planting, as that is the only practical way to make the mulch disappear from sight. The bed needs to be clearly defined in shape (the same as a wall would have done) and cleared out of all weedy, scraggly or scruffy plants (things I'm sure you didn't put there.) There could be some large shrubbery, including tree forms, toward the back of the area, but mainly what the slope needs is groundcover. That's the plants that are limited in height but tend to spread sideways, which is an advantage when one is trying to cover a lot of ground. You've got to use the right groundcover and it's hard for me to say from afar what that would be, But you could look around where you live and see what others are using for similar sized areas with similar conditions. (It's always good to get weeds completely under control before installing groundcover.) The other elephant in the room is the lawn. It's in pretty bad shape. And no matter how much $ or labor you dump into a retaining wall or planting, the whole picture is not going to look good when the lawn looks so bad. I say take all the money for the retaining wall, avoid harming any trees, put it in planting and lawn so that everything looks good, and have some left over for something else. It would be so much easier to do. The edge for a large groundcover bed could be the common "trench edge." I've seen many such beds, though, where the edge is simply kept defined by the lawn mower, with every mowing. You've got to take my picture with a grain of salt as it's highly conceptual and vague. And I'm no good at drawing lawns with heavy trees shadows, so that looks kind of messy. Anyway, I hope it'll give you the general idea.