you can grow just normal grass for them.
i used to try and grow cat grass for fonzie, but he was so enthusiastic about it he kept knocking the plant pot over and getting soil everywhere
![Sad :(](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/sad.gif)
he now has a harness and leash and goes out at night time to eat (and then puke) it up.
if you have a balcony, you can also buy catnip and valerian seeds for them! the cat nip is quite hardy...been growing for a good few years now, and i usually forget to water it!