Severely root bound black bamboo

Hi. I've recently purchased a black bamboo and it's roots looks crazy. Picture attached. I'm new to gardening so any advise on what to do would be really appreciated.... Especially with the thick wrapping around the middle. I'm guessing it's not good to replant it as it is.
I am planning on replanting into a much bigger pot.
Thanks

 

You could try to loosen that wrapping of roots around the middle with a hand fork or a screwdriver or something similar, using a prising motion, like opening a tin! Don't worry if some of the roots break, they will soon repair and regrow. Another option which I have done in the past is to cut the entire rootball in half with a pruning saw from the soil surface to the bottom of the rootball. You could then plant the two halves with a gap between them in the same pot or each half in a separate pot. They are tough plants and will soon recover. When potting, use a soil based compost like John Innes No 3 rather than multipurpose compost. A wide pot encourages more root growth as bamboos expand outwards. You could also remove some of the spindly or discoloured canes at the base which will also encourage fresh growth.

 

What are your long term plans for this bamboo?

The bigger growing Phyllostachys don't do well long term in pots.
They quickly use all the nutrients in the soil and get pot bound. Just end up looking tatty.

Your will do much better in the ground.
If well looked after (plenty of fertilizer and water) they won't run too much, and you can cut off any excess canes that you don't want.

Or alternatively swap it for one of the Fargesia which are clump forming, smaller and more manageable.

 

I agree with @Sirius, it will fare much better in the ground if you have space @Cerrisian. I grow several varieties of Phyllostachys in my garden. They have all been well behaved over the last 10 years and not become invasive, although I remove a large proportion of new canes every year. My shallow sandy soil also limits their growth. Your young bamboo should be fine in a larger container for a couple of years, but ideally needs then to be in the ground.

 

I have a number of Fargesia, Borinda and Phyllostachys in a relatively small garden.
Most are well behaved, expanding slowly.
The odd Phyllo sends out a runner, but I slice it off close to the main plant and pull it up.

The only bamboo that I felt was getting a bit out of control was my Chusquea gigantia.
The rhizomes were deep, and very solid. So not easy to remove. But it flowered and then died, so problem solved !