For a smoother slushy, consider freezing the rhubarb limeade in ice cube trays before blending. Adjust the amount of maple syrup to suit your personal preference for sweetness. The tartness of the rhubarb and limes can vary. Experiment with different herbs, such as mint or basil, to infuse additional flavor into the rhubarb limeade. For an adult version, add a shot of vodka, gin, or rum to each serving before blending with ice.