Bring 7 cups water to a boil over medium-high heat. Stir in 1 cup sugar, and cook, stirring constantly, 1 to 2 minutes or until sugar dissolves; remove from heat. Stir in lemon juice, mint sprigs, and lavender sprigs; let stand at least 2 hours.
Pour lemonade mixture through a wire-mesh strainer into a large pitcher, discarding herbs. Serve over ice. Garnish, if desired.
*2 tablespoons dried lavender flowers may be substituted.