When stored correctly, cannabis products can be kept for many years without the THC content dropping significantly. The larger surface area leads to faster THC degradation in marijuana compared to hashish and a higher sensitivity to external influences. (…)
Air and UV light promote the decomposition of THC into little or non-psychoactive substances. Temperatures up to 20° Celsius have only a minor influence on the shelf life. Higher temperatures accelerate the degradation of the THC contained. Mould can develop if the humidity is too high. In order to avoid a degradation of THC and odorous substances as well as the formation of mould spores, cannabis should therefore be stored in a dry, cool and dark place.
Quote: German Hemp Association