catnip from seed or start is super easy to grow. grows like a weed.
just average soil and plenty of sun/light for it. it can overwinter if it's rooted into the ground well enough.
just make sure to keep nipping off the tops as it grows and picking off flowers when they form to keep vegetative growth going on.
i just stuck my catnip in a 5 gallon bucket with old soil that i used on the indoor crops, stuck it outside, and it rooted through the drain holes in the bucket after 6 months. after a year i can't budge the thing really.
you can give the leaves to your cats fresh or dry it out and grind it up to put in toys or just to sprinkle on the rug. they love rolling around in that shit and getting it in their fur.
nip works differently on each cat, and some cats don't even like it.