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.
Once placed in the refrigerator, prepared tea lasts for around 5 days. If the prepared tea is frozen, it can last up to 8 months. As a general rule of thumb, though, prepared tea lasts as long as the ingredient that expires the quickest. For instance, if tea is made with lemon, it may expire more quickly.