Preparing your Own Chelates – Improving Your Hydroponic Nutrients


If you have already read my free ebook for preparing hydroponic solutions and you have already seen many commercial and other standard formulations you may be asking yourself if you will have problems with iron due to the unavailability of any chelating agents. The truth is that I have used formulations without any chelating agents several times and I haven’t had any problems when they are prepared by the ebook. However many of you may be interested in the addition of chelating agents and you may wondering how you may modify the spreadsheet or what you should add in order to generate the adequate chelates. On this post I want to explain a little bit how you can add chelating agents to your reservoir to chelate the salts mentioned on my ebook and how this can easily generate all the chelated metal complexes you need to avoid any solubility problems.

Simple metal chelate model representation

What is exactly a chelate and what are they good for ? A chelate is simply an organic molecule that “wraps” itself around a metal ion and prevents its precipitation, increasing its solubility. Chelates also diminish the amount of available metal ions to plants and therefore they slowly release the quantities of micro nutrients available for plant growth. There are many available pre-made chelates on the market such as Fe-EDTA. However, the cheapest way to generate chelates once you already have a standarized formulation based on simple inorganic salts is to add a chelating agent.

The most common of these agents is called Ethylendiamintetraacetic Acid (EDTA), a tetraprotic acid which is able to chelate most metals with a particularly high afinity for Fe. However, when you add only chelated iron, the fact that other metals start to compete makes the iron complex destabilize and the chelate is eventually destroyed. However, when we add the chelating agent we can make sure that we add enough to “wrap” Fe and other metals in such a way that the stability of the iron complex is guaranteed.

When we add the chelating agent we do not add EDTA (the acidic form) but we add it as a salt of another element, usually K-EDTA. Once this is added to the solution the EDTA quickly gets rid of K and goes for another metal – such as Fe – for which it has a much higher affinity. The chelating agent quickly forms complexes with all the metals it loves and you end up with a solution that is highly stable and not prone to any micro nutrient related precipitation. How much do you need to add ? Depends on your formulation. The spreadsheet download with the ebook shows the amount of chelating agent (K-EDTA) you need to add to the END solution after all micro nutrient concentrated solution additions have been done (this amount fully complexes Fe, Mn, Zn and Cu).



  • Chris
    February 28, 2011 @ 4:08 pm

    I’ve been told by Crop King that EDTA is poisonous to plants. He didn’t have a reference at hand, and I was wondering if you know of one.

    • admin
      March 1, 2011 @ 11:20 am

      Hi Chris,

      Thank you for your comment :o) Please remember Paracelsus’ concept of toxicity : Every substance, at a certain concentration, will be toxic. Certainly EDTA is toxic to plants when given in large dosis but when chelating micronutrients in sub-ppm concentrations it does absolutely no harm. EDTA has been widely used as a chelating agent for both hydroponic and soil iron fertilization for at least the past 70. I hope this helps :o)

      Best Regards,


      • January 1, 2019 @ 7:37 am

        Hi Daniel:
        I’ve used Ca EDTA with no luck. Phytotoxicity seems to occur and also precipitates very easily in Solution even with Ca(NO3)2 any idea why? What do you think of Glycine as Chelator?
        Thanks in advance.

  • Chris
    March 12, 2011 @ 5:16 pm

    Thank you Daniel.

    What do you have to say about organic chelators? I’ve read about citric acid, aminos, molasses, humic/fulvic acids, et. al. Are they worth anything? Any suggested application rates?

    • admin
      March 13, 2011 @ 2:53 am

      Hello Chris,

      Thank you for your comment :o) To the best of my knowledge there is no research which demonstrates any advantage to their use in hydroponic culture in general. They however do hinder the absorption of many micronutrients as they are very efficient chelators of certain metallic species. For example zinc gets very easily chelated by citrate ions so usually if you add a lot of citrate you’ll eventually get a zinc deficiency (this is what I have experienced on my experiments with this acid). An additional problem is that this chelating agents are “food” for microorganisms so they will increase the chances of outside microbe contaminations (including fungi and bacteria). Additionally plants do secrete oxalic, citric and similar acids through their roots so the little chelating benefit these substances could provide is probably already being “taken advantage off” within your plants micro-root environment. In the end I believe that most people use these things due to pure hype as experimental evidence up until now seems to suggest no significant difference from a nutrient availability point of view (at least in hydroponics). In the end a well-balance nutrient solution is all you need for very healthy plant growth. I hope this answers your question :o)

      Best Regards,


      PS : If you know of any peer reviewed sources which describe positive general usage of organic chelating agents in hydroponics please let me know as I have always been interested in this field :o)

      • Prabal
        November 15, 2016 @ 10:33 am

        Long back i think about 2004 i asked Dr Lynette Morgan how to make
        chelated iron without using EDTA as this was a very expensive chemical in India – Pondicherry – then.
        Her reply was some thing like
        A) 1 liter water + 150 g of Citric Acid
        B) 1 liter water + 216 g of Ferrous Sulphate.
        Mix A and B
        Then every 1cc contains 21.6 mg of Iron

      • December 31, 2017 @ 9:16 am

        Hello Daniel sir, Can we meet at Facebook or WhatsApp plz.

        • admin
          December 31, 2017 @ 10:16 am

          If you’re interested in meeting please feel free to book an hour of consultation time (120 USD) using either the booking link at the website or the site’s contact form.

    • Jim Zamzow
      March 18, 2019 @ 8:57 am

      There are at least two methods a plant absorbs nutrients, ions through active transport and organic micro clusters through endocytosis. That should help explain your organic vs chemical chelate question.jz

  • March 24, 2011 @ 3:49 pm

    Daniel there is some research that demonstrates certain qualities of citric acid as a chelator generally revolving around phytoextraction of heavy metals. To quote one piece “Organic acids like malic acid, oxalic acid and citric acid have been evaluated for mobilizing heavy metals like Cd, Zn, U, Cr and Ni in soils thus increasing not only the metal uptake but also translocation to shoot. Citric acid compared to EDTA was more effective in mobilizing Cr (Jean et al., 2008).” From
    Phytoextraction of heavy metals – the process and scope for
    remediation of contaminated soils by T Mahmood

    Another paper that may be of interest is:

    Comparison of synthetic chelators and low molecular weight organic acids in enhancing phytoextraction of heavy metals by two ecotypes of Sedum alfredii Hance

    Dan Liua, b, Ejazul Islama, c, Tingqiang Lia, Xiaoe Yanga, Xiaofen Jina and Qaisar Mahmooda

    Dr Lynette Morgan PhD has also run trials with fulvic acid. I found this quite interesting.

    • admin
      March 24, 2011 @ 4:12 pm

      Hi Rai,

      Thank you very much for your comment :o) Yes, there are many studies in the use of organic acid chelators for heavy metal absorption for soil reconstitution (decontamination). The focus of these studies is plant absorption and NOT crop yields, crop quality or the effect of organic chelators on regular nutrients like Fe and Zn. In summary yes, there is evidence that certain metal ion absorptions may increase with some organic acids but there is no information which states that this provides any increase in yields (two very different things). You also need to be VERY careful here regarding the ions you’re talking about, the fact that citric acid mobilizes Cr better does not imply that the same applies for other metals (for example Zn, Cr and Fe are VERY different).

      Regarding the fulvic acid papers, they are indeed interesting, I could only find those from 1980 onwards and they do seem to provide at least some limited evidence regarding the benefits of using fulvic acids in soilless culture. I would say that it would take tests on more plants and under more statistically rigorous conditions to convince me to implement these compounds but from the above study one could conclude that at least plants like tomato and cucumber might find some benefit. However it is important to note that fulvic acid does not have a fixed composition and therefore the results could have been related to the particular source (for example on this study> That said, thank you very much for pointing out those studies :o)

      Thanks again for your comment :o)

      Best Regards,


    • Sanjay Patel
      March 15, 2016 @ 11:51 am

      which chelator is better, fulvic or citric???

  • March 26, 2011 @ 8:19 am

    Daniel, yes there does seem to be very strong evidence demonstrating the chelation qualities of fulvic acid in hydroponics – and yes I agree that fulvic acid doesn’t necessarilly have a fixed composition albeit that we are years away from understanding FA and organisations such as the ISS can supply a 100% FA product (thus guaranteed fixed composition). The other thing that needs to considered is amino acids which are organic and have been conclusively demonstrated to increase yields in hydroponics.For instance, amino acid chelators such as glycinates (amino proteinates)which are metal ions chelated by glycines (I also believe they use lysergine among other amino acids to achieve a similiar thing).

    I did read some research which demonstrated that citric acid increased yields where EDTA didn’t (when discussing phytoextraction in a controlled hydro experiment – I will try to locate this research and provide you with a link). My point being that when research does not necessarily exist to support something this could simply mean no research has been undertaken that has supported a theory that then needs to be tested.

    For instance Yara are now conducting research on phasing out synthetic chelates and replacing them with organic chelates. EDTA is a large molecule and is not uptaken by the plant. It leaves the M ion on the roots and then is left in soil and solution. At this point it can chelate other metal such as Cadmium, lead etc. So the long term aim is to phase out the synthetic chelators and replace them with organic chelators such as amino acids.

    I think there are two schools of thought on organics in hydroponics but one school is coming to the fore. What is occurring now in hydroponics is the pahasing out of sterile systems by bio diverse hydroponic growing systems which incorporate organic components to sustain and encourage microflora. I think as time goes on you will see a lot of research that supports this approach and already there is a lot of very sound peer reviewed research that conclusively demonstrates the benefits of organics in hydroponics. This also applies to organic chelators.