It is my understanding that fertilizers are generally okay for about a year, but they start to deteriorate after that. The deterioration would be faster in a warm and damp environment. If it were mine, I would not take a chance with it.

Hmm, that reminds me I have some closet cleaning to do myself!

Will Creed
Indoor landscaper

See if there's a toll free number on the packaging. If not, you can find an information number on line. They will be able to answer the question for you.

The concept of CRF is a simple one: Manufacturers start with a granular soluble fertilizer, then coat it with a semi-permeable polymer membrane. As water passes through the membrane into the fertilizer core, nutrients within the fertilizer go into suspension (dissolve). Because the concentration of nutrients is higher inside the membrane, nutrients begin to diffuse out through the membrane by a natural process called osmosis. The osmotic release will continue until such time as there is no longer a nutrient concentration difference across the membrane, effectively, until nutrients within the CRF pellets are exhausted. So, CRF actually never goes bad. Even if it's exposed to some moisture and a portion of the fertilizer leaches out from the granules, only a small volume of fertilizer contained within the pellets is affected. As soon as the solute concentration in the area immediately surrounding the pellet equalizes with the concentration inside the pellet, fertilizer inside the pellet can no longer dissolve and pass through the membrane.

Al

Al, that makes a great deal of sense. Thank you! They should have stayed dry, so I'm good to go.

How about a water soluble granular fertilizer such as MiracleGro. How long will that store?

Indefinitely. Even if it gets all gunky from absorbing water from the air, it will still be equally effective as new product, though perhaps not as convenient to use. If it turns to a semi-liquid, remember to measure out less product because there will be little air in what you're using. This would, in effect, make a higher concentration using the same volume (all product - no air).

Al

Thanks again, Al! I've never had it get all gunky, just a tad damp, like slightly damp sand. You've saved me from buying a lot of unnecessary fertilizer!

Indefinitely. Even if it gets all gunky from absorbing water from the air, it will still be equally effective as new product, though perhaps not as convenient to use. If it turns to a semi-liquid, remember to measure out less product because there will be little air in what you're using. This would, in effect, make a higher concentration using the same volume (all product - no air).

Al