The easiest way to tell if your tea has expired is from an herbalist
Whether herbal, black, or green, all teas are made from dried plants that gradually lose their potency over time. If you store the tea carefully and keep it tightly closed and away from light, it can last up to two years. However, if your herbs are exposed to air, moisture, light, or heat, they will begin to break down more quickly.
The easiest way to check the freshness of your tea is with your nose, which is actually a pretty advanced chemical detector: get to know the aroma of fresh tea before you brew it. Then, if you ever doubt how old your herbs are, smell the leaves.
If you ever make tea with old herbs, don’t worry: the result will just be a boring brew. Of course, it will be a waste of time, water and heat, but not a big risk to your health.