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Shelf Life of Garden Chemicals

By Paul James

Much like the flavors of spices and seasonings in your pantry diminish over time, the effectiveness of garden chemicals can do likewise. But just how long do garden chemicals, whether synthetic or organic, actually remain effective? Or said another way, do they have a finite shelf life? Well, it depends on who you ask and the product in question.

And unfortunately, three of the major manufacturers of garden chemicals have different takes on the subject.

Scotts (which also produces Ortho products) says its products should be used within three years, although granular fertilizers with no additives such as herbicides should keep indefinitely. Bayer (the chemical (and aspirin) giant claims its products will keep indefinitely. And Bonide, which makes a number of synthetic and organic chemicals, says its liquid products have a shelf life of between three and 10 years.

Well, that certainly clarifies things, now doesn’t it? (Adding to the confusion, by the way, is the fact that expiration dates aren’t even required on product labels.)

However, the one thing all three companies agree on is that the effectiveness of their products can be greatly affected by how they’re stored. Specifically, they acknowledge that the shelf life will likely be reduced if the chemicals are stored where they’re exposed to extreme temperatures, as in above 90 or below 32 degrees Fahrenheit, or in areas of high humidity. And my guess is that at least one of those conditions probably can be found where you store your chemicals, such as a garden shed or the garage.

What’s more, the Big Three generally agree that once opened, the active ingredient in their products may change chemically and begin to break down, thereby decreasing its concentration and effectiveness. The product may also begin to form flakes, crystals, or sludge, making it impossible to mix or use in sprayers. Powders are especially prone to caking.

So what’s a gardener to do? Well, I do believe that granular fertilizers that don’t contain any herbicides should keep indefinitely, although organic fertilizers and soil amendments that contain beneficial bacteria and fungi such as mycorrhizae (both of which can be destroyed by temperature extremes) should be used shortly after purchase. Most liquid formulations – whether fertilizers or pesticides – should be used within two or three years, especially once they’ve been opened. I’m willing to guess that most gardeners have more than a few such products that need to be disposed of and replaced, and now is a great time to sort through your inventory.

But just how do you get rid of unwanted garden chemicals? Well don’t pour them down the drain or throw them in the trash! Instead, take them to the City of Tulsa’s Household Pollutant Disposal Facility. For details, go to

Note: Residents living in Bixby, Broken Arrow, Claremore, Collinsville, Coweta, Glenpool, Jenks, Owasso, Sand Springs and unincorporated Tulsa County can obtain a voucher from the Metropolitan Environmental Trust (918-584-0584) to drop off up to 45 lbs. of pollutants free of charge. Info is available at the same website above.

Happy gardening, y’all.

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