Prepare dates: Soak the pitted dates in hot water to soften while preparing other ingredients.
Rinse hibiscus petals: Rinse the dried hibiscus petals three times to remove any sand or impurities.
Prepare pineapple: Wash the pineapple thoroughly. Peel the pineapple, using both the peel and flesh. If concerned about pesticides, remove the thin outer layer of the peel before using.
Cook hibiscus and pineapple peel: Add rinsed hibiscus petals and pineapple peel to a large pot. Add enough water to cover (about 10 cups). Grate the ginger and add it to the pot. Bring to a boil over medium-high heat and let boil for about 5 minutes.
Blend pineapple flesh: Cut the remaining pineapple flesh into chunks. Blend with some water until smooth to form a pineapple paste.
Cool hibiscus mixture: Add ice to the hibiscus mixture to cool it down, or allow it to cool completely (can refrigerate overnight) before proceeding.
Add blended pineapple and dates: Add the blended pineapple paste to the pot with the hibiscus mixture. Blend the soaked dates with some of the soaking water until smooth and add to the pot. Stir well to combine.
Strain the drink: Pass the mixture through a colander to remove large chunks, then strain through a fine mesh sieve twice to remove fine particles and any remaining sand.
Add lemon juice and adjust sweetness: Squeeze lemon juice into the strained drink and stir. Taste and adjust sweetness by adding more blended dates or water as needed.
Chill and serve: Place the drink in the fridge to chill or serve immediately over ice.