We live in the NW and I'm looking to uproot and transplant a Japanese maple that was of substantial size when we moved into our house 5 years ago. It sits in a cedar box above ground but the seams on the box were starting to open and the fraying near the ground indicated that the bottom was probably removed. Anyway, a coworker who's in a Bonsai club said it would be okay to cut the roots. Turns out that there is a concrete slab under the pant and the tree rooted itself at the corners of the box. I am not at all savy when it comes to these things and don't want to kill the plant. I would like some height on the plant so originally thought i'd put it in a container. I wonder if the plant would be more happy connected to the ground and try instead to achieve some height by putting blocks under the tree, a enclosure around it and filling it in with soil? Any suggestions would be helpful. Thanks.
You could both leave it in place and get it quickly taller by selecting a suitable-looking branch from near the main trunk and training it up a secure stake for several years.
That's good advice and definitely feasible if the main branches are still flexible. And my neighbor has a really old established weeper that he's trying to get height on by just staking up the young branches next to the stiff older branches. Personally, I think that's going to look odd for many years, but he's willing to wait to get the shape he wants. It's all about what the individual wants from their tree. But for another option, here's an odd thought. Nine times out of ten the larger size maples I see in the PNW are over-buried. You might be surprised by how much height you can gain simply from proper planting. I transplanted a weeping japanese maple out of one area of my yard to another that the previous owner had planted. When I first moved in, I thought it was a little over-buried. So I scraped back the dirt (about four inches) until I could transplant. When I did pull it out, I was shocked to be able to easily pull off another four inches of loose topsoil. And then I went to work on the clay. By the time I got down deep enough that I could see a proper trunk flare, I had unearthed over a foot of buried trunk (for info on trunk flare: http://www.tlcfortrees.info/Planting%20Depth.htm). Then I planted my tree "high" with the bottom of the flare slightly above the surrounding ground. I ended up getting about a foot and a 1/2 of "height" just by transplanting. That being said, pictures of your project would help. Just how large is this tree? You mention a box, so that's adds size in my imagination and makes me think of larger caliper size both on the trunk and the branches. Did it root into the concrete in just five years? Or was it there when you moved in? Sounds like it's in its original nursery box from getting dug from a field? Has your coworker seen the tree or just given you general advice? Are they willing to help you transplant the tree? Odds are good that the roots going into the concrete are more for stability than nourishment. If it were my personal tree, I'd probably wait until December/January (you can search out info on the best time to root prune, there's been a lot of discussion on the site and the timing I mentioned is a personal preference) and then remove the box and cut the roots. I'd also look at the trunk flare to make sure it wasn't over-buried. There have been very few large trees that I've bought that haven't needed some TLC on the roots. And the ones that didn't were because someone else had done it first. So I'd probably also look for girdling and circling roots and address them. And if I wanted height on a weeper that was already substantially thick I would find a place were it could drape. For example, maybe put it in a nice pot that is then placed on a retaining wall or hillside. I'd choose a pot with a shape that would enable me to get the tree back out every few years to root prune it and treat it like a giant bonsai. Or maybe build up an island somewhere with this tree at the top, giving it room to cascade down.
