One warning about catnip plants if grown outside...(we have or had several in our yard) Once you start picking, pick all you want because once the scent of freshed picked catnip is in the air every stray for miles will find your plants and happily eat them down to the ground...lol
Also for those that don't know Cat Grass is really nothing more than young oats like they raise for horses, you can go to most feed stores and ask them for a handful of raw oats. ( some charge a small amount, other will just give you a handful)
Bring home, plant in a kitty friendly container and water as needed. Our cats love it.
Mel & Muse