Got 3 really fine looking 2-3 gal phormium at Home Depot ($16 apiece) labeled 'Apricot Queen', but they look more like 'Yellow Wave' to me. Their container is about 10" wide. The ivory ceramic container I want to put it in unfortunately has a narrow top--only 11-12" at top...it swells in an oval shape below, and has a height of 17".

I want to stuff around it a burgundy sedum with tiny leaves to drop over the edge. I'd be happy if the phormium stayed just the same size it is now, so I'm not after growth. But I don't know if their root systems go deeper than wide, or wider than deep. I know they're hard to repot, and I guess I'd have to eventually use a saw to split it in half.

My question is, would I be harming the plant by 'forcing' it into this situation? I'd appreciate any thoughts you may have.