My liquid fertilizer froze in my garden shed. Should I use it?

This is a common question that I am asked quite a lot in store.  Let’s talk about the considerations and how freezing can affect different fertilizer formulations and if that fertilizer should be used after it has frozen.  


Microbial Inoculants

Microbial inoculants are an essential component of modern gardening (and agriculture).  These types of products contain microbial life that improve soil health, reduce plant stress and assimilate nutrients in the soil.  Microbial inoculants have the shortest shelf life of all other liquid products– only lasting one to two years.  These types of products are the most sensitive to their environment, especially extreme heat and extreme cold.  Extremely warm temperatures can cause the microbes to activate inside the bottle and the excessive heat can “cook” the microbes, rendering them useless to the plant and soil.  If these products freeze solid, the spores can become damaged and again will be rendered useless to the plant and soil.   If this type of product does freeze solid, it is best to dispose of it per the SDS sheet and local/state regulations.


Liquid inorganic / Salt Based Fertilizer

These types of fertilizers have the longest shelf life of all other types of liquid fertilizers.  When stored at optimal conditions (50-80 degrees F, out of direct sunlight, minimal humidity) they have a shelf life of up to 10 years so long as the manufacturer’s recipe is stable. 


The main thing to avoid with these types of fertilizers is freezing.  Most liquid salt based fertilizers will have a freezing point lower than water, usually around 20 degrees fahrenheit.  If these products do freeze, it will have detrimental effects to the composition of the fertilizer.  Crystalline structures will form inside the bottle.  This is often referred to as “Fallout.”  When you shake the bottle, you will hear these crystals hitting the inside walls of the fertilizer bottle.  Because freezing can change the crystalline structure of the fertilizer, it is best to dispose of the fertilizer per the SDS and state/ local regulations.  


Liquid Organic Based Fertilizer

Liquid organic fertilizers are a good choice for gardeners that want to provide their plants with nutrients that come from a natural source.  However, these fertilizers present challenges when the temperatures drop below freezing.  It is important to note that for the purposes in this blog post, “organic” refers to the fact that these fertilizers were sourced from natural materials such as compost, manure, animal byproducts or other natural sources.  Freezing can affect the fertilizer’s nutrient content.  When water freezes, it can separate out from the other components of the fertilizer.  In turn this can cause nutrient imbalances and lock out.  It is best to dispose of this fertilizer per the SDS and state/ local regulations.



The best thing a gardener can do to preserve their investment in fertilizer is to prevent it from freezing.  Storing the fertilizer inside during the winter is the best way to prevent freezing.  Another tactic that could be considered by the gardener is to purchase fertilizer sizes that they will use up in one summer. Thus, not having to store any fertilizers at all.  Green Thumb Garden Supply carries most products in a range of sizes to satisfy the need of any sized garden.

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