Is Your Fertilizer Still Good?

I’ve worked for a fertilizer manufacturer for over ten years, and I often receive a phone call from someone asking if their bottle or bag of nutrients is still good to use. They rarely remember how long ago the product was purchased, and if we’re lucky, the label is still in good enough shape to know what it is. Smart companies like the ones I work for will have a lot number from each batch printed on the bottle, which makes product and date determination substantially easier. To help determine if a product has spoiled, here is a small tutorial plus tips on the best way to store your nutrients.

Liquid Inorganic and Synthetic Fertilizers

Liquid inorganic and synthetic fertilizers pose the least of challenges when it comes to product longevity. When stored in the proper conditions, these types of products can remain in usable condition for almost an indefinite amount of time. The ideal storage conditions for inorganic liquid fertilizers are a relatively dry environment with constant temperatures between 50 – 80 degrees Fahrenheit. In these conditions, the soluble salts found in the concentrated product should remain in solution without any issues, as long as the manufactures formulation is stable.

The main thing to avoid with these products is freezing temperatures. Because of their dissolved mineral compositions, concentrated inorganic liquids will freeze at a lower point than water. For the most part, they will not freeze until reaching below 20 degrees Fahrenheit. If they do freeze, the solubility of the minerals can be compromised, and crystalline structures will usually form within the bottle. This will have a detrimental effect on the balance of the formulation and can lead to inconsistencies in the mineral nutrient composition.

When this happens, it is usually best to dispose of the product in accordance with recommendations on the manufacturer’s Safety Data Sheet (SDS) and local/state regulations. To avoid freezing, try to keep the product in a temperature-controlled area like inside the house or a well-insulated (and preferably heated) garage. Storing the fertilizer outdoors or in an uninsulated shed is not recommended.

Inorganic and Synthetic Water-Soluble Granular Fertilizers

Similar to its liquid counterpart, inorganic and synthetic water-soluble granular fertilizer mixes are relatively easy to keep in optimal condition and can have a nearly indefinite lifespan. With these types of fertilizers, the main environmental condition to avoid is high humidity. Due to their highly water-soluble nature, granular mineral fertilizer will begin to solubilize in the presence of higher levels of water vapor in the air. The higher the relative humidity rises, the faster the product melts into a glob of gooey fertilizer mess, rendering it void of any reasonable use. Even after removing it from the humidity, the clumps of fertilizer that remain will not be nearly as water-soluble as before. Avoiding high humidity is true for both warm and cold temps. If there is heavy moisture in the air and the temperatures drop below freezing, crystalline structures can form since some of the fertilizer has solubilized. Once it warms back up, the quality of the fertilizer product will be compromised. The key for water-soluble inorganic nutrients is to keep the product as dry as possible at all times, and the bag or container kept closed when not in use. If the package that the product originally came in is not re-sealable, it is a great idea to transfer it into a different, sealable container. Just make sure to save the label for future reference.

Organic Plant Food Products

Organic plant food products present a different set of challenges when it comes to shelf and storage life. Liquid organic products that meet USDA National Organics Program (NOP) standards like fish emulsions, liquid seabird or bat guanos, and seaweed extracts are not allowed to contain chemical preservatives that prolong their shelf and storage life. Instead, the manufactures can use small amounts of phosphoric acid to stabilize the product by dropping the pH to 3.0 or lower: helping to keep the biological components from becoming active. When these components do become active, the stability of the product is minimized to the point where bacterial and fungal growth can occur. This growth is usually accompanied by an off-gassing that can cause the bottle to balloon and sometimes even explode at the seams.

In a retail setting, where the temperatures remain consistently around 70 degrees Fahrenheit and the products are away from direct sunlight, organic liquid fertilizers can usually remain stable up to five years or sometimes longer. It’s when the product is taken home by a customer and the seal is broken that the shelf life dramatically decreases. Once fresh air is introduced into the bottle, the effectiveness of the stabilization process can begin to erode. In an effort to prolong the storage life of an opened bottle for as long as possible, always store the product in a relatively cool area, void of direct sunlight. Heat and intense sunlight are most often the number one reasons why organic liquid plant nutrients go bad. Also, do not allow these types of products to freeze. Freezing will most definitely ruin the composition and solubility of the mixture. If an organic product does become active in the bottle and begins off-gassing or ballooning, it doesn’t directly mean that it has gone bad in the sense that it cannot be used. In this case, slowly remove the cap and carefully inspect the product. If there is visibly noticeable fungal growth, then I would advise not using the product because there is no clear way of knowing if the fungi will be beneficial or detrimental to the plant and root growth. Likewise, if the smell is abnormal or rancid, it is best to replace it with the new product and to dispose of the bad product properly. Liquid products that contain both organic and inorganic ingredients usually don’t meet NOP standards and will often have a chemical preservative to maintain stabilization over a longer range of time and conditions. Even so, these products should be treated and stored in the same fashion as true organics to ensure their maximum storage life.

Granular or Dry Organic Fertilizers

Granular or dry organic fertilizers such as bone meal, composted manures, and plant-derived meal products like alfalfa or neem seed meal tend to have a much longer shelf and storage life. These products undergo one or more of a variety of treatments to preserve their integrity for long periods of time. They can be heated, steamed, rinsed and dried, composted, and dehydrated to remove possible pathogens and remaining moisture. The result is a consistently dry product that has minimal biological activity. However, the introduction of moisture will re-activate the microorganisms present, and they will begin to grow and in turn, degrade the product. Granular or dry organics should always be kept in a tightly-sealed container or bag, away from any possible interaction with water. As long as these products stay dry, changes in temperature should have little effect on their quality. Regardless, it is always good practice to avoid extreme heat or cold when storing any fertilizer.

Microbial Inoculants

Microbial inoculants are by far the most sensitive to the environment in which they are stored. These products contain living spores of beneficial bacteria of fungi (often both) that can be easily harmed or destroyed. When it comes to liquid microbial inoculants, the most important aspect of storage is to avoid temperatures over 80 degrees. Warm temperatures can activate the product while still inside the bottle, and the excessive heat can more or less cook the tiny spores rendering them useless to the plant or soil. Some companies add organic materials into their microbial blends. This makes for a pretty impressive product, but if the spores do become active within the bottle, the organic components act directly as a food source for the microorganisms, and the product will inevitably go bad in a small amount of time. Always store these products in an area with temperatures between 60-80 degrees Fahrenheit and be sure to keep the lid on tight.

Granular water soluble microbial inoculants, just like water-soluble granular fertilizers, should be stored in sealed bags or containers in a cool and dry environment. Moisture will not only start to solubilize the material, but it will also activate the microorganism spores before they are ready to be used. Activating them within the package can ruin their quality, and if there is other organic material in the mix, they will begin to feed on them, and the product quality will diminish. As long as these products stay dry and are not stored in temperatures below 40 degrees Fahrenheit since cold can harm the spores, they will maintain their quality for quite some time.

An important distinction to make in regards to microbial inoculants is the fact that over time, the viability of the spores will naturally diminish. Storing them in the proper conditions helps to ensure that they remain viable for a longer period of time. Since their viability does decline, some states’ regulatory agencies require manufacturers to include an expiration date on the label. At the moment, this is typically a two year period. Regulatory labs are currently working on developing the best methods to enumerate healthy viable spores with the goals of creating guidelines for product testing and ensuring the consumer that the contents of the product match what is listed on the label. This is still a developing field of study, but after two years, many of these types of products will still have viable spores, even if they are lower than the numbers on the label. For best results, store microbial inoculants properly and use them within the two-year expiration date.

When it comes down to price per gallon or price per pound, quality fertilizers and other plant growth materials are not the cheapest purchase to make. Having to dispose of something that has gone bad when it could have possibly avoided if only a few different steps had been taken is a foolish way to waste money. Paying extra attention to storing a product in the proper conditions is a small step that can go a long way in maintaining a fertilizer’s quality over time.

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