In 2- to 3-quart pan over high heat, bring 4 cups water to a boil.
Meanwhile, trim off and discard tough ends of lemon grass and pull off coarse outer leaves. Thinly slice stalks.
Add lemon grass, thyme, mint, ginger, lemon slices, and tea to boiling water. Cover and remove from heat. Let stand (steep) 5 to 10 minutes.
Pour tisane liquid through a fine strainer into a teapot or pitcher. Serve hot, or cool with ice.