Plants need secondary macronutrients and micronutrients in smaller quantities than primary macronutrients, and yet deficiencies in the former can be just as harmful to growth and yield as deficiencies in the latter. Micronutrients are particularly prone to becoming unavailable due to nutrient lockout or precipitation from the nutrient solution. Chelation helps to prevent this.
In this blog post, we explain what chelation and chelates are, how they work and why they’re essential for nutrient uptake and utilization.
Chelate gets its name from Greek chelē (“claw”) because the chelating agent grips the metal ion like a lobster’s pincers. The process of binding the ion to form a chelate is called chelation.
Chelation offers several benefits:
Alters ionic form
Many micronutrients, as well as the secondary macronutrients calcium (Ca) and magnesium (Mg), are positively charged in their ionic forms (e.g., Ca2+ and Mg2+). Because root membranes carry a negative charge, these ions face resistance due to charge repulsion. Chelation neutralizes or reverses the ion’s charge, allowing it to cross the root membrane more easily.[3]
Prevents oxidation and precipitation
Changing the ion’s charge also helps prevent reactions with oxygen and negatively charged hydroxide (OH⁻) ions—both abundant in the growing medium— that would otherwise form insoluble compounds. For example, the plant-available form of iron is ferrous (Fe²⁺); however, without chelation it can oxidize into ferric (Fe³⁺), which plants cannot absorb.[4]
Improves nutrient availability
By keeping nutrients soluble and mobile, chelation increases their availability for plant uptake, improving absorption and reducing the risk of deficiency.[5]
Types of chelating agents
Chelating agents vary in effectiveness, which is determined by their stability—measured by the stability constant. The higher the stability constant, the stronger the bond between the chelate and ion, and the more available the nutrient is for plant uptake.[6]
Chelating agents can be either organic or inorganic.
Natural chelating agents (organic)
Natural chelating agents are often byproducts of decomposed organic matter and include:[7]
- Organic acids (e.g., humic and fulvic acids)
- Amino acids
- Lignosulfonates
- Lignin polycarboxylates
- Sugar acids and derivatives
- Phenols
- Polyflavonoids
- Siderophores
- Phytosiderophores
Because these chelating agents are organic, they’re more easily absorbed by plant roots, and their smaller molecular size allows for greater penetration. They also pose less risk of scorching, and any unused chelating agents will biodegrade.[8] Some organic chelating agents, such as fulvic acid and amino acids, are effective across a wide pH range.[9] Fulvic acid is particularly effective, greatly enhancing nutrient uptake.
Plants themselves can also make certain chelating agents. For instance, mugineic acid is a phytosiderophore—a nonprotein amino acid secreted by roots—which, once it captures and delivers a nutrient ion to the root, becomes available to chelate another ion.[10]
- Organic acids (e.g., humic and fulvic acids)
- Amino acids
- Lignosulfonates
- Lignin polycarboxylates
- Sugar acids and derivatives
- Phenols
- Polyflavonoids
- Siderophores
- Phytosiderophores
Because these chelating agents are organic, they’re more easily absorbed by plant roots, and their smaller molecular size allows for greater penetration. They also pose less risk of scorching, and any unused chelating agents will biodegrade.[8] Some organic chelating agents, such as fulvic acid and amino acids, are effective across a wide pH range.[9] Fulvic acid is particularly effective, greatly enhancing nutrient uptake.
Plants themselves can also make certain chelating agents. For instance, mugineic acid is a phytosiderophore—a nonprotein amino acid secreted by roots—which, once it captures and delivers a nutrient ion to the root, becomes available to chelate another ion.[10]
Synthetic chelating agents (inorganic)
Examples of synthetic chelating agents include:[11]
- Ethylene diamine-tetra-acetic acid (EDTA)
- Diethylene-triamine penta-acetic acid (DTPA)
- Ethylene-diamine-di-(o-hydroxyphenylacetic acid) (EDDHA)
- N-(hydroxyethyl) ethylene-diamine-triacetic acid (HEEDTA)
One study found that among the synthetic chelators tested, EDTA and DTPA were the most effective for recirculating hydroponic nutrient solutions.[12] EDTA is widely used because it forms a stable complex through four points of attachment.
Synthetic chelating agents (inorganic)
Examples of synthetic chelating agents include:[11]
- Ethylene diamine-tetra-acetic acid (EDTA)
- Diethylene-triamine penta-acetic acid (DTPA)
- Ethylene-diamine-di-(o-hydroxyphenylacetic acid) (EDDHA)
- N-(hydroxyethyl) ethylene-diamine-triacetic acid (HEEDTA)
One study found that among the synthetic chelators tested, EDTA and DTPA were the most effective for recirculating hydroponic nutrient solutions.[12] EDTA is widely used because it forms a stable complex through four points of attachment.
Synthetic chelating agents (inorganic)
Examples of synthetic chelating agents include:[11]
- Ethylene diamine-tetra-acetic acid (EDTA)
- Diethylene-triamine penta-acetic acid (DTPA)
- Ethylene-diamine-di-(o-hydroxyphenylacetic acid) (EDDHA)
- N-(hydroxyethyl) ethylene-diamine-triacetic acid (HEEDTA)
One study found that among the synthetic chelators tested, EDTA and DTPA were the most effective for recirculating hydroponic nutrient solutions.[12] EDTA is widely used because it forms a stable complex through four points of attachment.
However, these attachment sites may bind the nutrient too tightly, reducing its availability to plants. On the other hand, if the bond is too weak, the nutrient may be released too soon, leading to loss and inefficiency.
Chelator performance also depends on growing conditions—especially pH. EDTA is most effective in slightly acidic to neutral conditions, specifically at pH 6.5 or lower,[13] which aligns with the ideal hydroponic pH range of 5.8–6.3 for cannabis. If pH rises too high, the metal ion can precipitate or become unavailable to the plant.
Other factors, such as temperature and the type of growing medium used, may also influence the effectiveness of synthetic chelators like EDTA. For best results, growers should choose chelating agents suited to their specific conditions to ensure optimal nutrient availability.
Using chelated nutrients
We recommend using a combination of chelating agents, including natural sources. A diversified approach helps ensure consistent nutrient availability and absorption. Fertilizers that include a range of chelating compounds, like Emerald Harvest’s premium line of hydroponic nutrient solutions, offer reliable nutrient delivery across diverse growing conditions.
Emerald Harvest Team
[1] National Cancer Institute. n.d. “Chelating Agent.” Accessed March 16, 2025. https://www.cancer.gov/publications/dictionaries/cancer-terms/def/chelating-agent
[2] Gangloff, W.J., D.G. Westfall, G.A. Peterson, and J.J. Mortvedt. 2000. “Availability of Organic and Inorganic Zn Fertilizers.” Colorado State University Agricultural Experiment Station Technical Bulletin TB 00-1. https://webdoc.agsci.colostate.edu/AES/aes/pubs/pdf/tb00-1.pdf.
[3] Manik, Afsanabanu, Honnappa, B.S. Umeshbabu, Padmashree, S. Surekha, and Anil Jadhav. 2023. “Function of Chelators in Nutrient Supply to Plants.” Biological Forum — An International Journal 15 (10): 309-313. https://www.researchtrend.net/bfij/pdf/Function-of-chelators-in-nutrient-supply-to-plants-Umesh-Babu-BS-59.pdf.
[4] Liu, Guodong, Edward Hanlon, and Yuncon Li. 2012. “Understanding and Applying Chelated Fertilizers Effectively Based on Soil pH: HS1208, 11 2012.” EDIS 2012 (11). https://doi.org/10.32473/edis-hs1208-2012.
[5] Manik, Afsanabanu, Honnappa, B.S. Umeshbabu, Padmashree, S. Surekha, and Anil Jadhav. 2023. “Function of Chelators in Nutrient Supply to Plants.” Biological Forum — An International Journal 15 (10): 309-313. https://www.researchtrend.net/bfij/pdf/Function-of-chelators-in-nutrient-supply-to-plants-Umesh-Babu-BS-59.pdf.
[6] Sekhon, B.S. 2003. “Chelates for Micronutrient Nutrition Among Crops.” Resonance July: 46-53. https://www.ias.ac.in/article/fulltext/reso/008/07/0046-0053.
[7] Ibid.
[8] Birla, Devilal, Shubham Jaiswal, Subirá Sahoo, Surendra Bhilala, and Devendra Singh. 2021. “Organic Chelates; Types and Roles in Soil Fertility.” Agriculture & Food: E-Newsletter 3 (6): 150-152. https://www.researchgate.net/publication/354527214_Organic_Chelates_Types_and_Role_in_Soil_Fertility.
[9] Manik, Afsanabanu, Honnappa, B.S. Umeshbabu, Padmashree, S. Surekha, and Anil Jadhav. 2023. “Function of Chelators in Nutrient Supply to Plants.” Biological Forum — An International Journal 15 (10): 309-313. https://www.researchtrend.net/bfij/pdf/Function-of-chelators-in-nutrient-supply-to-plants-Umesh-Babu-BS-59.pdf.
[10] Liu, Guodong, Edward Hanlon, and Yuncon Li. 2012. “Understanding and Applying Chelated Fertilizers Effectively Based on Soil pH: HS1208, 11 2012.” EDIS 2012 (11). https://doi.org/10.32473/edis-hs1208-2012.
[11] Sekhon, B.S. 2003. “Chelates for Micronutrient Nutrition Among Crops.” Resonance July: 46-53. https://www.ias.ac.in/article/fulltext/reso/008/07/0046-0053.
[12] Vadas, Timothy M., Xinning Zhang, Ashley M. Curran, and Beth A. Ahner. 2007. “Fate of DTPA, EDTA, and EDDS in Hydroponic Media and Effects on Plant Mineral Nutrition.” Journal of Plant Nutrition 30: 1229-1246. https://doi.org/10.1080/01904160701555119.
[13] Virtual Museum of Minerals and Molecules University of Wisconsin Madison. n.d. “EDTA.” Accessed March 19, 2025. https://virtual-museum.soils.wisc.edu/display/edta/