From the Star K simple dry herbal teas do no need supervision. Presumably this does not only apply to tea.
Herbal and Medicinal Teas: Popular herbal teas include Chamomile and Mint Teas. Echinachia tea is a well known medicinal. Generally made from dried herbs, leaves, and roots, they are intrinsically kosher and do not need to be certified. Herbs are typically dried on dedicated equipment in dedicated processing facilities, by having warm air blown over them.
The above is true for herbals and medicinals that are simply dried herbs. However, if additional ingredients such as flavors have been added, they would need to be reliably certified. One of the most popular brands of teas, “Celestial Seasonings,” has many herbals and regular teas that have been certified by the Star-K since the mid-1980s.
And from Scroll K
Herb blends – Require reliable certification.
Herbs, dried – Leaves, seeds and spices, without added ingredients, does not require certification, unless it is produce of Israel, then it require reliable certification.
Herbs, freeze dried – Require reliable kosher certification.
