Does Tomato Fertilizer Potency Stay Strong Over Time?

“Does opened tomato fertilizer potency remain consistent even when the fertilizer sits in the garage from year to year?”

That was a question posed to us by a Tomato Dirt reader. And it’s a good one.

The short answer is this: granular fertilizer does not lose its potency over time unless it has been exposed to moisture. Water breaks down its components. (Remember how your dad always wanted to apply fertilizer to the yard right before rain?)

That's why it's important to keep fertilizer in a sealed, protected container (here are some good containers to consider.)

In addition, many gardeners recommend storing opened fertilizer on a surface other than concrete, because concrete easily absorbs and transfers moisture. According to Scott's Miracle-Gro company (makers of Miracle-Gro Tomatoes, granular fertilizer stays potent indefinitely if kept dry.

Liquid fertilizer is another matter ... after opening, it can lose potency within 6-10 years.

Having said that …

Use plastic storage boxes to store extra tomato fertilizer.

Tomato Tone contains special micro-organisms that the company claims will not be as potent nor do their job as well if not used within two years – even though the fertilizer elements stay potent indefinitely. Check the product’s label for “Use by [certain date]” or “Packaged Date: [certain date].” Even so, if fertilizer is a bit old, you can still use it and gain some benefit for your tomatoes.

Here's what the good folks from Louisiana State University Agricultural Center have to say:

"Many people find themselves wondering if their fertilizer from several years ago is still viable for the upcoming season. Generally speaking, fertilizer does not lose its potency as long as it has been protected from moisture in the air." 

Bottom line when it comes to tomato fertilizer potency ...

Store your tomato fertilizer in a dry place. If you have extra fertilizer after you have harvested the last of your tomato crop, you can even using covered, plastic containers to overwinter leftovers to use next season.

More on tomato fertilizer ...

How to use tomato fertilizer to get the best production ...

Kinds of tomato fertilizer ...

Organic tomato fertilizer advantages and disadvantages ...

Epsom salts: a natural tomato fertilizer ...

Tomato fertiizer question: will this tomato fertilizer work for you?

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