If properly dried, shrooms can be kept for more than a year without noticeable potency loss. (I performed a bioassay of 2g (dried,1 year old) P. cubensis and compared with 2g (dried, new harvest) P. cubensis).
Drying:
I put my shrooms on a grating and dry them by fanning at room temperature for about 36 hours. Then I put the shrooms in a box sealed from air in the presence of silicagel. The silicagel in the box absorbs all the moisture from the air and the shrooms will dry completely. Silicagel is necessary to remove all the remaining moisture from the shrooms. Properly dried shrooms are very crispy and can be pulverized easily by crushing them with your fingers. If all the moisture is not removed, storage times decrease significantly (oxidation of psilocybin/psilocin goes a lot faster if water is present).
Storage: Dark in an airtight box with silicagel in the basement (15°C).
I believe that properly dried shrooms can be kept indefinately.
Don't put dried shrooms in the fridge. A fridge is a very humid environment.