Cover 1/4 cup lavender flowers with 1 cup boiling water and let steep 10 minutes. Strain.
Combine lavender infusion with 1-12 oz. can frozen lemonade concentrate and 1 cup grape juice. Add 1 quart water. Chill. To make: fill glass 1/2 full of lavender lemonade over ice, then top up with lemon-lime soda or champagne. Add a lavender sprig.