We have noticed that kittens don't respond to catnip much... they have to be adults. Maya (age 4) even as an adult is only modestly affected by catnip.

However, Weezie is quite habituated to it...and asks for it daily if we don't offer it. There seems to be a variation to catnip response in our home, over the years. They play alot and chase each other after a catnip splurge. I put it in a large paper grocery bag, to keep the mess down, and this also concentrates the vapors. I grow my own in a very deep planter/urn outside, and can get 3 crops of bushy plant....by cutting it back every month or so leaving 4 leaves behind. I then dry it upside down, in a paper bag, and then put the leaves (throw out the stems), in an air tight jar or ziploc plastic baggie. When I give it to them I rub the leaves between my fingers to release the scent and oil for them. This works better for us, because the soil in the planter is better than that in our yard! Catnip grows best in partial sun and good moisture.