Soluble fertilizers and ProTeKt 0-0-3 have an indefinite shelf life, but you might find that the granular fertilizers (like 20-20-20, 24-8-16, 30-10-10, ........) can absorb moisture from the air and turn into a sludge if not stored in air tight containers. That doesn't mean they're spoiled or unusable, but figuring out the proper dosage would be difficult when it changes to a liquid.

Al

Thanks, an e-mail response from Dyna-Gro confirmed the same!