The roots (rhizomes) may not go down to the bottom of the container, given the depth. If you want to have a layer of rocks at the bottom (for drainage?), do it. The main issue is that over a number of years the bamboo may get rootbound. How easy will it be for you to get in there and divide the plants with a saw or a shovel? Bamboo roots go to the edges of containers and exert considerable pressure, and they fill containers with a network of very tough, woody rhizomes. This makes division and extraction quite difficult. People who grow bamboo in narrow or small containers often construct them with a removable side so they can get at the root ball and divide it more easily. I recently helped someone divide a bamboo that had been planted in a half barrel, and the only way we could do it was to destroy the container.

As for your soil, the bamboo will be fine in it. But something that fancy is not necessary. I typically pot up bamboo and throw in whatever dirt I have readily available to fill the container and they do fine. Bamboo are not very finicky when it comes to soil.

Thanks for your reply!

By sheer luck, the container is built in such a way that the slats can be easily removed to gain access to the roots. In a few years, it will be easy to deconstruct and then reconstruct the container if need be.

Since I had already purchased the materials, I went ahead and used the aforementioned mix. It was definitely more work than it had to be. I used almost three-hundred pounds of mix -- yikes!!!

It was difficult getting the bamboo out of the nursery pots, and I did end up having to rip one apart, so I understand what you are saying about the outward force of the woody rhizomes.

While the plants were somewhat rootbound in their nursery pots, I didn't cut the roots/rhizomes at all. Was this a mistake?

No, you did just fine. When you re-pot bamboo you don't want to unnecessarily cut the roots or even try to untangle them. You just de-pot and put the whole rootball in the ground.

Now, in several years, when you have to or want to divide the plants, use a long root pruning saw or a Sawzall to cut the root mass into big chunks, each with several culms. Although you will obviously be disturbing the rhizomes by this carving up activity, you should be fine as long as you divide the root mass into large root balls. I usually try to divide out rootballs that are at least the size of basketballs.

I'd love to know more about your container. I'm looking for something similar and am trying to figure out if I'll need to build it myself.

I second kcmbamboo, if you can post a picture of your container I would love to see it. Thanks.

Sorry, I don't have any photos. I can say that the planter was fairly easy to build.

The tricky thing is going to be finding a way to keep it from freezing in the winter. Originally, I thought that I would be able to use a dolley to wheel them into the garage, at least for the first winter, but the planters are massively heavy and the bamboo plants that I purchased are taller than I was expecting (which is a good thing). Either way, I knew that it would outgrow the garage, so I'll just have to come up with some insulation method when winter approaches.

I'm in a slightly milder area, but I can tell you my low tech system for wintering containers with marginal plants. I have too many trees, thus tons of leaves fall. On dry days I fill black plastic bags with leaves, tie off and start stacking them on the side of my garden shed.

After my container plants are good and cold, then I surround the vulnerable pots with these stuffed bags. I turn the tied off part down, to stop them filling with rain. On larger pots the bags are stacked one on top of another.

I also got some free thick foam board from a neighboring concrete contractors company, because they had edges broken and were headed for the dumpster. They're huge! Thinking of your container shape, that might be something you could work with. Build a shell for the existing box, with the foam inside. Very posh and much less 'trailer park than my black bags. ;)

That's a great idea, plaidbird! I'll have to look into it and see if I can get some foam board to cover each side of the planters. Do you think the foam board, secured at the top and bottom of each side with one-by-fours would be enough protection? Or would I be better off covering the planters with foam board and then an outer layer of plywood over the entirety of each side?

Here's another overwintering question -- I watched a video about "flat covering" bamboo. Basically, you tie the culms together and then pull the bamboo down to ground level, stake them so they stay pretty much flush to the ground, and then cover the bamboo with plastic or burlap.

Will the bamboo culms be harmed? Will they stand up straight again after being hunched over all winter?

I have gone a little stake crazy with my newly planted bamboo, making sure that it is staked and supported so it stands tall and straight in the wind. The idea of bending it over, espcecially so severly, all winter is kind of hurting my brain. However, it is in a very windy spot, and I know that it'll suffer greatly if left unprotected all winter.

I suppose layered would add some additional protection, same as the double paned windows do. But will you really need it? Sorry I'm not up to snuff on your zone. My point was originally more the aesthetics of the planter. I mean, if it's front center, the xmas lights would pull the eye from the plain foam board I guess. Or...maybe do up a REALLY big wreath for it. Hey, xmas lights add warmth. ;)

The interesting thing about the type of foam board I got from the concrete supply place is how different it is compared to the type I've seen sold to home owners for insulating their houses, at places like Home Depot. Though I imagine if a place sells concrete for large enough jobs, they must have this stuff. This stuff is heavier, tougher, and a bit thicker. No idea what the contractors do with it. It's a wholesale only place and they sell to some really big jobs. Government type stuff ( bridge/highway sized things), besides jobs doing additions to schools, apt. buildings,etc. I do wonder what they use it for.

I watched a video of a guy doing that bend it over type of winterizing. I'm with you..yikes ! Anybody leans too much in my garden, they get whacked off. My bamboos are all older, so they need whacked now and then anyway. I'm the token grandma here, and my bamboo addiction started 30 years ago. That first rhizome was a Vivax (a leaner ), so it's pretty impressive now. I'm still learning and seeing new things all the time. I love seeing the photos when members show their plants. Glad I don't have to make those kind of winter choices.

Over the years I have had occasion to run out and wrap a plant or shrub in whatever I could dig up. I've used my own blankets in an emergency. Yes, the neighbors notice. They roll their eyes and say something funny about how I love my plants. LOL

Google Reemay, it's nice stuff, and it lasts from year to year. Not sure if it's available in an affordable size for bamboo though. I have some pieces that I know are at least 15 years old, but I've not used them every year, so I'm not sure how long it would last that way.

With luck, someone with more info about your climate will come along and be able to help.

You might also try the search engine at http://www.bambooweb.info/. Those guys know their stuff. I cruise quietly through their forms once in awhile. Much of it's over my head, but it's fun. :)

Here is a link that might be useful: http://www.bambooweb.info/