It’s *Cymbopogon nardus*

Cymbopogon nardus is the main one, though Cymbopogon winterianus is also common.

Both are true citronella grasses, but C. nardus (often called Ceylon citronella) is the species most repellent products are based on. C. winterianus (Java citronella) has a higher citronellal content, so it’s used in some commercial oils too. If you’re buying a plant to keep mosquitoes away, look for Cymbopogon nardus.

Just don’t get it confused with lemon grass (Cymbopogon citratus), which smells similar but won’t do much for bugs.

Now you can impress your friends at the garden center.