Today I brought in the last of tender bonsai, to await spring on a lighted table in the dining room. Our two new kittens have convinced themselves that this must be the new alternate kat-box. I have a squirt bottle to disabuse them of that idea.
Oh.... yeah, keep an eye on that! yuck, if you blink and miss them getting into the dirt to hide their mischief.
Two kittens to try and keep an eye on!! Good luck Coppice and I hope they grow out of using your bonsai as a litter tray soon.
I don't know if it would work but I have heard that you can take some old spoons, stick the handles in the pots at an angle and that will discourage cats.