Compact it down (not squish, this is to save space) and put it in your desired storage container. Leave it outside for a day or two, or just put it in the sun. It should dry out within a few hours if it is just moist and it is in the sun. Once it is dry, close the container and store it.
I have all of my bales of dry Sphagnum on the floor of my greenhouse under the growing shelves. They don't need a certain temperature/light.
Just make sure they are 100% dry or they may start growing mold/bacteria.
As jeremyinsf said, add water when you want to use it and it will be back to its original state. Good luck!
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