Using two separate containers, soak the nuts in 4 cups of water and the flowers in 4 cups of water in the refrigerator for 24 hours.
Strain the nuts and discard the soaking liquid. Transfer them to a high-speed blender.
Strain the hibiscus liquid into the blender, discarding or composting the flowers.
Blend on high until the mixture is completely smooth, about 1 to 2 minutes. Strain the mixture through a cheesecloth.
Stir in the honey and vanilla, and serve over ice.