When people think of organic agriculture, they often imagine products free of synthetic chemicals and pesticides. While that’s part of what qualifies products for organic certification, it’s a limited definition. In this blog post, we’ll discuss the regulatory and scientific meanings of “organic” and how fertilizers containing organic ingredients affect hydroponics.
Regulatory meaning
What does it mean when a product is labeled organic?
Fruits, vegetables, meats, packaged foods and other agricultural products can be labeled organic only if certified through a government-approved program. In the US, this falls under the USDA’s National Organic Program (NOP).[1] It is illegal to display the USDA Organic Seal—or use the word organic on packaging, apart from listing certified ingredients—without approval from a USDA-accredited certifying agent (Figure 1).[2]
What does it mean when a product is labeled organic?
Fruits, vegetables, meats, packaged foods and other agricultural products can be labeled organic only if certified through a government-approved program. In the US, this falls under the USDA’s National Organic Program (NOP).[1] It is illegal to display the USDA Organic Seal—or use the word organic on packaging, apart from listing certified ingredients—without approval from a USDA-accredited certifying agent (Figure 1).[2]
Figure 1. The USDA has four labeling categories for organic products. With the exception of products that list organic ingredients, if a producer wishes to use the USDA Organic seal or label the product as organic in any other way, they must obtain organic certification. Image source: USDA. n.d. “Organic Labels Explained.” Accessed August 14, 2025. https://www.ams.usda.gov/sites/default/files/media/OrganicLabelsExplained.png.
Organic certification involves the entire production process—not just avoiding synthetic chemicals. Growers must follow approved methods. In the US, they must apply only organic fertilizers, with limited exceptions for inorganic options listed in the National List of Allowed and Prohibited Substances.[3] Organic growers may use raw organic inputs like manure or consult the Organic Materials Review Institute (OMRI) for approved products.[4]
Scientific meaning
Chemically, an organic compound is any substance containing carbon with either a carbon-hydrogen (C-H) or a carbon-carbon (C-C) bond. In plant nutrition, organic ingredients refer to natural substances derived from plants (e.g., biomass, extracts, byproducts), animals (e.g., manure, blood meal, fish hydrolysates) or minerals (e.g., Epsom salt, rock phosphate) that support plant health through nutrients or bioactive compounds. Rich in organic matter, they act as slow-release nutrient sources, support microbial activity and, in traditional agriculture, improve soil structure.[5]
Some organic ingredients enhance nutrient uptake without supplying significant nutrients. Examples include humic and fulvic acids, seaweed extract, kelp and guano. These ingredients supplement base nutrients rather than replace them. For instance, kelp extract promotes root growth and stress tolerance, but its macronutrient content is typically negligible.[6]
Organic fertilizers versus organic ingredients
The differences between the regulatory and scientific meanings of organic have important implications for hydroponics.
Above all, growers should understand that organic ingredients can still benefit plants, even when included in fertilizers that aren’t certified organic by regulators, and can even help address some of the challenges associated with certified-organic fertilizers in hydroponic systems.
Using organic fertilizers in hydroponics
While it’s possible to fertigate hydroponically cultivated crops with certified-organic fertilizers, they pose several challenges:
Absence of microbes
Plants absorb nutrients in ionic form, so organic compounds must first break down into simpler molecules, a decomposition process that requires microbial activity. For example, nitrogen in manure exists largely as proteins, but soil microbes mineralize these proteins into plant-available ammonium (NH4+).[7]
Unlike soil systems, hydroponics lacks native microbial populations. To use organic fertilizers effectively, growers must introduce microbes—such as nitrifying bacteria via bioreactors—to convert organic nitrogen into available forms.[8]
Absence of microbes
Plants absorb nutrients in ionic form, so organic compounds must first break down into simpler molecules, a decomposition process that requires microbial activity. For example, nitrogen in manure exists largely as proteins, but soil microbes mineralize these proteins into plant-available ammonium (NH4+).[7]
Unlike soil systems, hydroponics lacks native microbial populations. To use organic fertilizers effectively, growers must introduce microbes—such as nitrifying bacteria via bioreactors—to convert organic nitrogen into available forms.[8]
Slow release
Even with microbial activity, organic nutrients take time to convert into ions.[9] In soil, this de facto time release benefits crops by providing steady nutrition and limiting environmental losses due to volatilization, leaching and other factors.
In hydroponics, however, nutrient loss is less of a concern, and precision is critical. The delayed availability of organic nutrients can make it harder to fine-tune feeding schedules.
Using organic ingredients in hybrid fertilizer—a win-win
Feeding organic ingredients to hydroponic plants does not pose the same challenges as certified-organic fertilizers, provided the ingredients are soluble. Liquid organic inputs like compost teas and fish emulsions integrate easily into a nutrient regimen and offer a range of plant health benefits. For example, studies show that adding compost teas to hydroponically cultivated baby leaf red lettuce improves growth and quality,[15] while seaweed extract significantly increases branching and leaf production in hydroponic purple basil and peppermint.[16]
Some fertilizers blend organic and inorganic nutrients, offering the advantages of both. These hybrid fertilizers supply readily available nutrition while incorporating organic components for long-term plant health. However, because they contain both mineral and organic ingredients, they do not qualify for OMRI certification and cannot be used in certified-organic grow operations.
Combining organic and inorganic inputs can enhance yields and improve nutrient uptake. Many nutrient companies, including ours, develop blends like teas, tonics and bloom boosters that combine inorganic minerals with organic compounds to optimize plant nutrition.
One study on hydroponic lettuce found that a mix of 50% inorganic fertilizer, 25% seaweed liquid extract and 25% cow urine produced the highest fresh and dry weight.[17]
Combining organic and inorganic inputs can enhance yields and improve nutrient uptake. Many nutrient companies, including ours, develop blends like teas, tonics and bloom boosters that combine inorganic minerals with organic compounds to optimize plant nutrition.
One study on hydroponic lettuce found that a mix of 50% inorganic fertilizer, 25% seaweed liquid extract and 25% cow urine produced the highest fresh and dry weight.[17]
Conclusion
Organic takes on different meanings in regulatory and scientific contexts. Organic fertilizers are approved for certified-organic production. Organic ingredients, on the other hand, are natural nutrient sources that may or may not meet organic certification standards.
Understanding these distinctions helps hydroponic growers make smarter choices. Using 100% organic fertilizers in hydroponics is challenging due to the absence of soil—and therefore the naturally occurring microbes needed to break down organic matter—as well as the risk of pH fluctuations, microbial contamination and slow nutrient release.
Hybrid fertilizers that combine inorganic nutrients with organic ingredients, however, can offer the best of both worlds: precision fertigation and long-term plant health.
Emerald Harvest Team
[1] The USDA is the United States Department of Agriculture. Some states may have their own organic programs that allow them to regulate organic production within their jurisdictions.
[2] USDA Agricultural Marketing Service. n.d. “About Organic Labeling.” Accessed August 20, 2025. https://www.ams.usda.gov/rules-regulations/organic/labeling.
[3] USDA. n.d. “The National List.” Accessed August 14, 2025. https://www.ams.usda.gov/rules-regulations/organic/national-list.
[4] OMRI is a third-party nonprofit accredited to ISO 17065 standards by the USDA Quality Assessment Division to review inputs, including fertilizers, intended for use in certificated organic production.
[5] Pokorny, Kym. 2025. “Choosing the Right Fertilizer for Your Garden.” Oregon State University Extension Service, March. https://extension.oregonstate.edu/news/choosing-right-fertilizer-your-garden.
[6] Card, Adrian, David Whiting, Carl Wilson, Jean Reeder, and Dan Goldhamer. 2015. “Organic Fertilizers.” Colorado Master Gardener GardenNotes. https://cmg.extension.colostate.edu/Gardennotes/234.pdf.
[7] Pettygrove, G. S., A. L. Heinrich, and D. M. Crohn. 2009. “Manure Nitrogen Mineralization.” University of California Cooperative Extension Manure Technical Bulletin Series. https://manuremanagement.ucdavis.edu/files/134367.pdf.
[8] Kechasov, Dmitry, Michel J. Verheul, Martina Paponov, Anush Panosyan, and Ivan A. Paponov. 2021. “Organic Waste-Based Fertilizer in Hydroponics Increases Tomato Fruit Size but Reduces Fruit Quality.” Frontiers in Plant Science 12: 680030. https://doi.org/10.3389/fpls.2021.680030.
[9] Ronzoni, Ryan, and Neil Mattson. 2020. “A Guide to Home Hydroponics for Leafy Greens.” Cornell Controlled Environment Agriculture. https://www.purdue.edu/hla/sites/master-gardener/wp-content/uploads/sites/9/2022/10/Guide-To-Home-Hydroponics-For-Leafy-Greens-Ronzoni-and-Mattson-2020.pdf.
[10] Electrical conductivity
[11] Parts per million
[12] Ronzoni, Ryan, and Neil Mattson. 2020. “A Guide to Home Hydroponics for Leafy Greens.” Cornell Controlled Environment Agriculture. https://www.purdue.edu/hla/sites/master-gardener/wp-content/uploads/sites/9/2022/10/Guide-To-Home-Hydroponics-For-Leafy-Greens-Ronzoni-and-Mattson-2020.pdf.
[13] Ibid.
[14] Kano, Kazuki, Hiroaki Kitazawa, Keitaro Suzuki, et. al. 2021. “Effects of Organic Fertilizer on Bok Choy Growth and Quality in Hydroponic Cultures.” Agronomy 11 (3): 491. https://doi.org/10.3390/agronomy11030491.
[15] Szekely, Iris, and M. Haissam Jijakli. 2022. “Bioponics as a Promising Approach to Sustainable Agriculture: A Review of the Main Methods for Producing Organic Nutrient Solution for Hydroponics.” Water 14 (23): 3975. https://doi.org/10.3390/w14233975.
[16] Laribi, Bochra, Hibat Allah Annabi, and Taoufik Bettaieb. 2023. “Effects of Ulva intestinalis Linneaeus Seaweed Liquid Extract on Plant Growth, Photosynthetic Performance and Water Status of Two Hydroponically Growing Lamiaceae Species: Peppermint (Mentha x piperita L.) and Purple Basil (Ocimum basilicum var. purpurascens Benth.) South African Journal of Botany 158: 63–72. https://doi.org/10.1016/j.sajb.2023.04.049.
[17] Muhammad Harjoni Kilowasid, Laode, Sitti Fadhillah Arsani, Trsjia Corina Rakian, Rachmawati Hasid, Waode Siti Anima Hisein, and Andi Nurmas. 2022. “Use of Seaweed Liquid Extract and Cow Urine for Lettuce Growth in Hydroponic System.” E3S Web of Conferences 361: 04027. https://doi.org/10.1051/e3sconf/202236104027.