In a few places in my yard I'm struggling to control the expansion of LOTV. But in other spots, I'm trying to establish it. Several years ago in the fall, I cut many very heavy slabs 6 to 8 inches deep, 1 to 2 feet wide and 2 to 4 feet long, from an area where I wanted to remove LOTV, and moved them to three places I wanted to add LOTV and one place intended for only storage over winter. Where I wanted LOTV, I left significant space between those slabs (to reduce total work) assuming they would fill in quickly. In two target locations, I dug out rocks and roots to a foot down, then laid in big rocks all just over a foot high all around the boundary, then laid a 4 to 6 inches of better soil at the bottom, put the slabs in and filled better soil around them.
Every fall after that, I pulled the rocks up one at a time, cut the LOTV rhizomes running under the rocks and put the rocks back. Even the first year, the LOTV sent rhizomes almost to the far side of the rocks. But for several years there was zero fill in between my slabs. In this 2016 photo, you see the first time a few shoots filled in between two slabs (crowding and leaning outward from each slab makes it look like less gap than there really is).
I did careful exploratory digging two years ago between slabs and found no hint of any underground growth (no roots, no rhizomes, nothing). But under the rock border (where I don't want it expanding) there was plenty to remove every fall, even though that is much further from original slab edges than the centers of gaps that won't fill.
LOTV seems to detect nearby rocks and grow at full speed under the rock to find the other side, while not growing into easier empty space in other directions. In just one year from fall 2015 to fall 2016, a long thick cord grow to one of the rocks (up-slope back of this photo) then 6 inches down, 9 inches across and 6 inches up to get around that rock, then 14 more inches horizontal (I had to tunnel to remove it) to start a pip far underneath the blue bugle in the background of this photo (I think the slope confused the LOTV, because that pip was the right depth relative to the plant it left but way too deep under the up-slope). That is absurdly vigorous expansion growth for a plant that won't fill in the empty space right beside it.
The spot where I intended to store LOTV just over one winter, I instead left it years and didn't move any until summer 2016. Originally, I dug into hard packed rocky soil just big enough to hold several slabs pressed together. I didn't loosen any soil under or around. Years later those slabs had virtually no outward root expansion but very vigorous downward root growth (below the bottom of the original 6 to 8 inches). In re-transplanting, I couldn't get under the new root growth because of rocks, so I had to cut it off at the original 6 to 8 inch depth. That was a massive cutting job. It had really grabbed hard onto the ground below in the few years after first transplant.
In these and various other LOTV activities, I have observed that better and less rocky soil (as I provided in the target transplant areas) makes LOTV stay green long past the time each late summer when the never transplanted clusters (and those transplanted with less destination prep) turn brown. LOTV (at least mine) turn brown long before almost anything else and the ones that last longer look better. So the prep is helpful. But its underground expansion perversely avoids the easier directions and forces itself in the direction where winding past big rocks is most difficult.
