Whole leaf tobacco should be stored at a relative humidity (RH) of 75% or lower. By keeping filler in low case (RH ~ 60%) and binder or filler in medium case (RH ~70%), it will be ready for rolling right out of the container (bag, etc.). Medium case wrapper will require some additional humidification prior to use. The leaf that is maintained in high case (RH above 75%) is ready to roll but may mold if stored in that condition.
b. Temperature stability
As discussed in detail for the storage of cigars, storing the whole leaf in a relatively stable ambient temperature is important. If the temperature swings rapidly, moisture will condense in portions of the leaf and may lead to mold.
Cigar leaf (whole leaf) from wholeleaftobacco.com is usually shipped in sealed, vapor-proof bags. Unopened, the leaf can be stored in the bag for at least a few years, provided the ambient temperature is relatively stable.
Once such a bag is opened, it can still serve for excellent storage, so long as care is taken in opening it initially (cut it carefully just below the heat seal using a pair of scissors), and it is promptly re-closed each time that you remove the leaf from it. Press out all the excess air. Fold the corners of the open end to a right angle, then tightly roll and flatten the entire open end over itself several times. Follow this with clamping the rolled edge flat, using a chip-bag clamp or two or three clothespins. Simply taping the rolled end will allow it to leak air and vapor.
If you store the whole leaf within large, plastic tubs, it will gradually dry. Once completely dry, the tobacco is at zero risk of developing mold. Tobacco will not age further, so long as it is totally dry (out of “case”). Tobacco that is out of the case will instantly crumble to fragments and dust if handled or dropped in that state. Should the tobacco become completely dry, just mist it lightly with non-chlorinated water, close the container, then recheck it in a day?