Sticking my neck out here, but the Catnip Nepeta is actually Nepeta Canaris (which suggest dogs to me, but what do I know??) butter all is the answer to that one!
If you want to thin out to replant, you can be awfully posh and buy an aluminium dibber, or you can be a slob like me and use an ice lolly stick. Just gently tease the roots apart, as long as you get the main tap roots intact it'll be fine. Then re-pot. They should take in decent compost as long as the cats don't get there first.
You also get the pleasure of eating the ice lolly!