Using a knife and cutting board, chop the watermelon into roughly 1-inch cubes to facilitate blending. Gather all ingredients nearby.
Add the watermelon cubes and chopped basil leaves into the blender jar. Pour in the freshly squeezed lime juice. If desired, add honey or agave syrup for extra sweetness.
4 cups watermelon cubes
Secure the lid on the blender and blend on high speed until the mixture is completely smooth, approximately 30 seconds. You should see a vibrant green liquid with tiny seeds evenly distributed.
Stop the blender and open the lid. Pour the smoothie into chilled glasses. Observe the bright color and tiny seed specks, with a smooth, slightly pulpy texture.
Serve immediately with a sprig of basil or a lime wedge as garnish for visual appeal and freshness.
4 cups watermelon cubes