Squirt guns/plant sprayers are very effective, but if you aren't there
to catch them, according to a book on cat training I got recently, an
upside-down mousetrap will do the trick. You put it somewhere where
it will be triggered by the cat -- maybe under a piece of paper beside
the plant or something, then when the cat steps on it, the snap scares
it enough to make it leave the area alone, at least for a while. If
you put it upside down, you won't catch kitty's feet -- or nose.
Amazingly, our foster kitty has left all my plants alone. She wasn't
even that interested in the cat grass I grew for her, but you could
try that too, if you can make the kitten understand which pot is for
him/her. I put mine near the food dishes.
People who rescue abandoned kitties get lots of brownie points
somewhere in the great scheme of things... don't they?

Alison