Bring rhubarb, sugar, water and rose petals to a boil a large pot over high heat. Once boiling, reduce to a simmer and cook for 12 minutes.

Strain mixture in a fine mesh sieve then set the syrup aside to cool. Refrigerate for 2 hours before serving.

Add vodka and sparkling water to a large pitcher. Add rhubarb syrup and stir. Pour into cocktail glasses filled with ice, garnishing with a stalk of rhubarb and either mint or basil leaves.

Remaining rhubarb syrup will keep in the fridge up to 10 days.