A tablespoon is a non-scientific but very widely used unit of volume, which works very well in cooking, herbal medicine, etc. It is represented by a capacity of one tablespoon which varies from roughly 15 mL in the US to 20 mL in Australia.
1 If tea is properly stored, it can potentially last up to a year for green and black teas. White tea lasts about six months before it isn't as good in quality as when fresher. Stale tea (or bad tea) will taste flat, as if you're drinking paper.  Glass or ceramic containers are fine provided that they're opaque.
At the end of the day, we put any left over tea into a glass jar and refrigerate it. Chaga tea has the same flavor hot or cold and makes a delightful cold drink as well. You can keep your Chaga tea in the refrigerator for up to 14 days.