Why does my catnip (nepeta cataria) smell like low-grade lemon balm? To add to my confusion, they look nearly alike.
I’ve discovered that the various catnip plants growing around my yard smell different.
For example, the potted plants I picked up at a nursery have a faint skunk-like odor, which intensifies when dried.
On the other hand, seed grown catnip have a faint minty-citrusy scent. I’ve observed that the minty scent intensifies in catnip grown in-ground versus container-grown catnip. Or maybe I’m just imagining it.
I had forgotten I had dumped some potting soil laced with catnip seed in my flower bed and the seedlings emerged between the perennials, well protected by its taller neighbors. Catnip is supposedly a mint relative, but I can’t attest to its invasiveness. I am waiting to see if this colony will survive the winter and spread during the warm seasons.
A side-by-side comparison displays how catnip can be easily confused for lemon balm: look for the fine hairs on catnip leaves and the golden hue on lemon balm leaves. Here’s an article enumerating the differences.
Lemon Balm closeup 
Catnip closeup 
In-ground catnip behind a grow bag of lemon balm
Regardless of the smell, my cats still react the same way to the skunk-odor catnip and the mint-scented catnip. Here’s Conan going after the mint-scented variety.
It’s not difficult for the cats to distinguish between catnip and lemon balm. The cats have a habit of destroying catnip plants whenever they are in reach, so identification is easy usually in the aftermath. As a result, I have elevated the potted catnip plants and take cuttings to hand out to the catkids.
A takeaway from all this is to label your seeds and cuttings!