That’s very narrow. Can you train something on a trellis in that space?

I could do that but not sure I could get the density I would prefer. I would also like to do the same plant along a short fence on the periphery of the yard to tie it togethe.

In Hawaii skinny hedge is made with several species of Panax or Aralia from the genus Polyscias.

a pic of the situation would be worth a thousand words of speculation ...

im thinking garden curtain ... if your going to have to build a trellis structure anyway.. just make it a curtain rod ...

would you actually have room to get in there.. and maintain whatever you planted .. nothing is going to grow that thin entirely by itself.. and will need training or pruning by you to fulfill your goals ...

ken

https://duckduckgo.com/?q=hot+tub+garden+curtain+&t=ffcm&iar=images&iax=images&ia=images

Plants have a way of growing how they like not how you like and honestly how will you trim this without making a mess in the spa . Post some pics but honestly a hedge is the wrong choice from what I imagine from your post.

I saw a hedge around a hot tub in Alameda (zone 9 or 10) of Podocarpus maki that they sheared. When I saw it, it was covered with cones, and really decorative. I have no idea how long one can continue to shear it - it's slow growing and has dense foliage, so perhaps for quite a while.

Thank you for all of your comments. I am now thinking of a slat wall with spaces to hang plants and maybe some candles for ambiance and perhaps a shelf for drinks

You'll probably like that better - all plants drop spent parts, having to find something that never flowered or fruited at all could be pretty limiting and as mentioned shearing a formal hedge would generate a lot of falling bits each time it was done (you'd definitely have to have a lid you could put over the spa each time).