I have a ceramic container that is 2 feet tall but only about 1 feet in diameter and I have no idea what to use it for. Any recommendations? Can you put a mandarin tree in it? Something else that needs long roots but won't grow unwieldy?
Thank you!

Most woody entities make deep roots. Any that do should love this, like a Dracaena, Schefflera, false Aralia, Gardenia. Probably mandarin as well but not something I'm qualified to suggest.

A pot that shape will be more likely to tip-over if outside when windy.

But if it does not have a hole in the bottom for excess water to drain out, it might be best used as a cache pot. If it is difficult to find a pot that fits in without falling in too far, you can put some rocks or bricks in there until the inner pot rests at the desired level.

Bromeliads in tall containers

Thank you very much for the ideas and the pictures

I moved two 2½' tall containers down to our rural cabin property to flank the steps. It's a simple cabin with simple wood porch and steps and I thought they might make a statement. I thought they might decorate the entrance a bit. I would also recommend such tall pots for any plants that have a big tap/main root and not so many feeder roots (like a Ming Aralia).

ohh ohh, I know this answer.
Giant canna..
they love to have wet feet, so the deep narrow pot is ideal. They get 4-6 ft tall and will Balance the height of the pot.

I love bromileads, I have a bunch of multigenerational plants. They are beautiful, but they are epiphytes...

A traditional tall Sanseveria (snake plant/mother in law's tongue)would also look great

My pot is only 12" tall, but heres mine indoors in NY zone 6
I think it would do very nicely

You can grow tree peonies.

Lameri, did you decide on something?

I've been trying to get my hands on a tree peony for at least 3 years.. they're not that easy to come by, very expensive, they are done blooming by early june. they are not very tolerant of frost, so keeping roots above ground in a pot ls a very bad idea, I think.