1. In a 4- to 5-quart pan on high heat, bring 3 quarts water to boiling. Add hibiscus blossoms and cinnamon stick. Cover and simmer over low heat for 15 minutes. Let cool about 1 hour.
2. Pour tea through a strainer, lined with a double thickness of cheesecloth, into a pitcher. Discard residue in strainer. Pour tea, hot or cold, into ice-filled glasses. Add sugar to taste.