Gardening supplies can be damaged by increased precipitation and cold temperatures during the winter season. Simply leaving them out in a damp barn or storage shed, where they can be affected by melting snow or fast changing temperature conditions will not be a good idea. Even if some lawn fertilizer might be more resilient, it can still be heavily damaged in such cases, and other gardening tools and materials might be even more sensitive.
The general consensus between experts is that homeowners have to store their gardening equipment and products in a dry place where the temperature is stable. While you won’t need climate control, it’s important to at least make sure that your items are on a shelf or on a sturdy, dry surface that isn’t affected by the cold or by occasional flooding when the temperature drops.
If you store your organic fertilizer properly and make sure that it makes it well through the winter, you might even have enough fertilizer to avoid buying any new bags. Then you can use it for your lawn and garden once the spring comes, and it will behave just as well as if it were brand new – even if it’s more than 1-2 years old already.