The Difference Between Organic and Synthetic Plant Fertilizers: Breaking Down the Bottle

By Lacey Macri
Published: November 7, 2019 | Last updated: April 8, 2021 12:18:11
Key Takeaways

It’s high time to debunk some of the myths circulating about both organic and inorganic nutrients. Paying close attention to the ingredients contained in these products, as well as educating yourself on how, why and where they were derived from, will help you make better decisions about what nutrients to use in the growroom.

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Powerful buzz words like “sustainable” and “organic” continue to gain traction within the indoor gardening industry. Societal influences, along with a menagerie of scientific findings, promote these terms to help shift people’s mentalities toward a greener planet.


While many growers are more than willing to contribute towards a healthier planet, how are our consumables affecting this movement?

We hear a lot of competing theories on this subject that influence our decision-making as buyers. In this article, I will go over some of the ingredients commonly seen on the labels of fertilizer products, and how these ingredients affect the health of your plants, the planet and you.


Organic Fertilizers

While many studies indicate growers can achieve superior results using organic fertilizers, we have to be selective when choosing to use them. The true nature of some of these products is merely hiding behind its label, as words like “organic” may give growers a false sense of security in the products they are buying.

“Gardens that rely on water-soluble nutrients, such as nutrient film technique, stonewool and deep water culture, will typically suffer due to the low water solubility of organic fertilizers,” says Chris Durand, senior superintendent of agriculture at UC Davis, on the drawbacks of using organic fertilizers.

“The process is also slowed down by the extended amount of processing time it takes to break down the nutrients in organic fertilizers through the microbial activity for plants to be able to absorb them.”


This is significant in that, as many growers know, time is of the essence when it comes to cultivating high-yield plants. When things go sideways in the grow room, it almost always takes twice as long to correct it.

In addition to delayed response times and decreased solubility, some organic fertilizers have also been found to fall short in the hygiene department. Some common sources of organic nutrients come from earthworm castings, seaweed, alfalfa meal, blood meal, bone meal and fish emulsion. Others include magnesium sulfate, potassium sulfate, gypsum and rock phosphate.


While some of these sources excel with few, if any, risks, in some cases there is more to consider than meets the eye. For example, fish emulsion has sometimes been found to contain toxins in it that the fish absorbed while it was still alive that could potentially wind up in your finished product.

The good news about residual nutrients, however, as Durand says, is that “when a system is properly flushed, there is a reduced amount since plants are put into deficient growth conditions prior to harvest.”

While many would argue that organic growing is the one and only way to grow, there are definitely some things to keep in mind before starting out.

Read More: Building the Perfect Organic Fertilizer

Synthetic Fertilizers

Synthetic fertilizers sometimes get a bad rap for not being as environmentally friendly as their organic counterparts. While in some cases this may be true, there are a lot of synthetic nutrients out there that are as safe, if not more so, than many other products. First, let’s look at the most common sources of synthetic nutrients and what classifies them as inorganic in the first place.

Most popular nutrient products include a list of all the chemicals contained in the bottle. But how safe are these chemicals?

“Many non-organic nutrients are purified and processed versions of organic fertilizers, like magnesium sulfate and potassium sulfate,” Durand says. “Naturally mined sodium nitrate is reacted with potassium chloride to form potassium nitrate. Most synthetic phosphorus is processed organic rock phosphate.”

The purpose of these processes is to reduce heavy metals and change the nutrients into a form readily available for plants. Some of these aren’t a far cry from being classified as organic materials themselves.

There are also nutrients derived from a completely artificial process that are by no stretch of the imagination organic, but is this a bad thing? Nutrients such as calcium nitrate, phosphoric acid and ammonium nitrate are formed through a process called Haber-Bosch.

Durand explains that during the Haber-Bosch process, “nitrogen is pulled from the atmosphere and converted into ammonia, a form that is useful for plants. From there, the ammonia is transformed through chemical processes to other useful synthetic nutrients like calcium nitrate, ammonium nitrate, ammonium sulfate and phosphoric acid.”

The Haber-Bosch process is the backbone of modern agriculture and represents almost 2% of worldwide energy consumption. Without this source of nitrogen, it would be impossible to feed the 7 billion people and counting on the planet. It’s examples like this that help shed light on some of the truly sustainable features of certain non-organic processes and products alike.

One thing to keep in mind when using synthetic nutrients is that one of the most common mistakes growers make is overfeeding their plants. This can lead to nutrient toxicities and premature/frequent reservoir changes. In this scenario, some environmental contamination may occur when the unused nutrient solution is dumped.

The best way to prevent this is by closely monitoring your plants’ needs using meters and a trained eye in an effort to provide only what plants need and nothing more. Keep in mind that overfeeding can happen whether you are using organic or synthetic nutrients.

Read More: What Exactly Makes a Fertilizer Sustainable?

Just because a product is not organic does not mean it isn’t sustainable, safe or effective. And just because a product is organic, doesn’t automatically make it safe. When used correctly, both synthetic and organic fertilizers are safe to use. It’s important to familiarize yourself with the ingredients in the fertilizers you buy, regardless of their classification.

Choose products that have gone through adequate analysis and inspections to ensure their quality. Visit the Association of American Plant Food Control Officials website for resources that help promote the safe and effective use of fertilizers and the protection of soil and water resources. You can also contact your local department of agriculture for a list of registered products that have undergone the processes required for legal commercial sale.

Read Next: Building an Effective Fertilizer Regimen


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Written by Lacey Macri

Profile Picture of Lacey Macri
Lacey Macri works as head of sales at CleanGrow, focusing her time on business development within the company. She received a bachelor’s degree in communications and psychology from the University of California, Davis, in 2011, where she worked at the California Aggie student newspaper on campus.

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