Shop for Pet Supplies & Wildlife at The Home Depot. Since our catnip is grown, processed and packaged without any pesticides or chemicals, it is safe for cats to enjoy. Kittens usually develop a response to catnip after 6-9 months of age, which for most cats is a fun, focused burst enthusiasm that mellows into purr pleasure. The aromatic oils in catnip fade naturally over time. When your cat s interest in catnip and catnip-filled items changes, you will know it is time to add fresh catnip. Keep catnip fresh by resealing pouch after each use and storing in a cool, dark place out of your cat s reach.