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.
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 precipiation. 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).

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28 Responses

  1. Chris
    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
      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, Daniel
  2. Chris
    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
      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, Daniel 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
        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
  3. Rai
    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
      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, Daniel
    • Sanjay Patel
      dear, which chelator is better, fulvic or citric???
  4. Rai
    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.
    • admin
      Hi Rai, Thank you for your comment :o) However make sure you always support what you say with links to the peer reviewed search you're talking about. Despite my research I have never found a study which examines yield in hydroponics with either organic chelators (such as citric acid or aminoacids) or even fulvic acids, so I would be thrilled to actually see some research being posted instead of just mentioning its likely existence. The theory that EDTA cannot enter plant roots is also misleading, EDTA is not that "big" and plants have been shown to take in even tremendously large structures (like some polyoxometalates), EDTA can be found in plant tissue analysis on even leaves so the fact that it is "big" does not pose any absorption problem. By comparison fulvic acids are much bigger. As always I am keen to accept new ideas so feel free to post publications DIRECTLY related with YIELD and organic chelators. Thanks again for your post, Best Regards, Daniel
  5. Rai
    Just a quick correction (typo) IHSS (International Humic Substance Society). Also what's certain Daniel is people oversimplify the nature of microflora and organic biochemistry so research still has much to discover. My bet though - organic chelators are the future.
  6. Rai
    Yes of course you are right. Plants will uptake some EDTA but a lot is left in solution or soils (hence research into organic chelators that aren't left lying about in soils to chelate heavy metals by credible organisations such as Yara). Re organic chelators and EDTA... I'll find some more shortly. BTW. I find your comments about organics in hydroponics interesting and am keen to learn more. Plant uptake of 14C-EDTA, 14C-Citrate, and 14C-Histidine from chelator-buffered and conventional hydroponic solutions Auteur(s) / Author(s) BELL Paul F. (1) ; MCLAUGHLIN M. J. (2) ; COZENS G. (2) ; STEVENS D. P. (2) ; OWENS G. (2) ; SOUTH H. (2) ; Chelator-buffered hydroponic solutions provide low and buffered free-metal concentrations and allow the easy calculation of nutrient species expected in these solutions. Some researchers suspect that the solutions allow plant uptake of chelates and that this uptake explains the failure of the free-ion activity model using these solutions. To determine the amount and method of chelate uptake, swiss chard was grown in solution culture in growth chambers for about three wks and then transferred to solutions containing 14C-EDTA, 14C-citrate, or 14C-L-histidine for a 21-hour assay. Much higher root and shoot 14C were found from treatments containing metabolites histidine (2706097 shoot Bq 14C) or citrate (2241 953 shoot Bq 14C) than EDTA (280110 shoot Bq 14C). Passive transpirational flow could explain all of the EDTA uptake, but active uptake would be required to explain most of the citrate and histidine uptake even assuming some adsorption of ligand bound to roots. Swiss chard grown in solutions with the same total EDTA concentrations, but different amounts of Fe bound to EDTA, had >3-fold differences in root and shoot 14C concentrations. In a second experiment, swiss chard roots removed more EDTA from solutions containing mostly M-EDTA0 than M-EDTA1- or M-EDTA2- (288 140, 245051, and 192559 Bq 14C, respectively) suggesting plant selectivity for EDTA and a non-apoplastic route of uptake or an effect resulting from root cell-wall adsorption. Results indicated buffering of metals by ligands allowed some ligand uptake with much more uptake occurring with metabolites citrate and histidine than EDTA. A passive or indiscriminate form of uptake does not appear to explain all EDTA uptake with a selectivity by swiss chard for M-EDTA complexes of lower charge.
    • admin
      Hi Rai, Thank you for your reply :o) I think that you're not understanding my point of view very well. There is a lot of evidence about absorption and about the fact that organic chelators do get into plants more effectively than EDTA or DPTA (I am in no way saying this is not the case). What I am saying is that you cannot make the assumption that a higher absorption implies better plant yields and better crop results. What I am saying here is that there is no study I have been able to find which has shown that organic chelators provide ANY improvement in yield. The problem here is not demonstrating absorption but correlating better absorption with better yield. It can be the case that better absorption of an organic chelator might lead to worse crop quality as its has been demonstrated for several organic acids which are excretion by products (see here for an example : Again, studies about absorption say nothing as this is already known and not relevant to the problem of yield. What I would be very interested in is a study which measures PLANT YIELDS against organic chelators, because otherwise you simply cannot say they are better than EDTA or DPTA (they must give better yields, not merely better absorption which you cannot assume to correlate). Thanks again for your comments, Best Regards, Daniel
  7. Rai
    Daniel, I aren't necessarily saying that organic chelators are better (although potentially they may be) - it is more about the research now being conducted to created biodegradeable chelators/sequestering agents and existing technologies such as glycinates which are already in use in hydroponics and fields. I personally think the research has some way to go and unfortunately most agricultural research is conducted on soil grown produce and not hydroponics so what is found in soil needn't apply to water based systems. It interested me how you said that citric acid should be avoided and yet I cannot find any research to support this and given citric acid is a weak chelator, has a low molecular weight, and is used in lab experiments as a pH down (particularly in microbe research) I have a problem with this given for many years I have used citric acid as a pH down with great end results.I also use kelp (Acadian), molasses and fulvic acid and trichoderma and bacillus strains to create a biodiverse environment and haven't had pythium for many years. Have you got links to research pertaining to citric acid in hydro systems? I'd like to read the outcomes because perhaps it is feasible that it (citric acid) should be avoided for this purpose.
    • admin
      Hi Rai, Thank you for your comment :o) I do not say that citric acid should be completely avoided, as a matter of fact there are a few articles on the website on how to use citric acid as a buffer and the great effects you can see when using this in the appropriate way. The only thing I advocate for is for a very moderate and careful usage. For example some people wanted to use citric acid in concentrations as high as calcium (to chelate all calcium) something which is quite absurd as you would completely lock out zinc due to excessive chelation. The other problem is that calcium citrate is rather insoluble depending widely on pH so you run the risk of massive salt precipitations if you aren't careful and add too much. I experienced this myself on a medium sized system -luckily my personal system - with bad consequences (micro precipitation through all micro sprinklers causing an added labor cost to clean everything up). So what I am saying is not that citric acid should not be used but that using it in excess to do things like "chelating all calcium" is in fact absurd. Regarding microorganisms, I use trichoderma strains with great success as well added with lecanicillium lecani which has been a blessing for insect control :o) Thank you very much again for your posts, Best Regards, Daniel
  8. Rai
    OK I misinterpreted what you were saying. And yes it is an absurd idea to think you can chelate all calcium with citric acid. It is probably also pointless to chelate all calcium. Thanks for the feedback and yes Trichoderma is very good stuff!
  9. [...] A little info on EDTA as a chelator of metal ions. [...]
  10. Roberto
    Hey Daniel love your site and was wondering if you could send me the spreadsheet, I don't see the download for the ebook on your site any longer. Thanks for the great app.
    • admin
      Hi Roberto, The spreadsheet was replaced by HydroBuddy (it is no longer available for download), Best Regards, Daniel
  11. Roberto
    I don't see the spreadsheet in HydroBuddy Daniel?
    • admin
      As I said before the spreadsheet was REPLACED by HydroBuddy it is NOT included within it
  12. Roberto
    Can you finish the article so I know how to make chelates? Thank you in advance
  13. Angelo Moscariello Basile
    Daniel. I have heard about metalosate. A type of organic or amino chelate. Do you know anything about it?
  14. Yadava
    Sir can i know that How to prepare different concentration Iron chelate splution? chelating agent is EDTA
      Hello I'm looking for Method of production Iron chelate please guide me If you like this article Is it possible I have it?
  15. rakesh ranjan
    can anyone tell me how the zinc edta 12% can be manufactured?
  16. Izhar
    Can we use Acetic Acid as Chelating agent, I am referring to commercial grade 98% Acetic Acid.
  17. Can any one guide me how to make any micronutrient cheleted? Or adding cheleted micronutrient in liquid solution made of seaweed and amino acids?
  18. marc
    Hello, your writing on this page is very impressive! So impressive, that I have to ask for advice here. But my topic is about supplements for humans, specifically about d-asperic acid. The chelated version of daa is super expernsive, so I am looking for a way to chelate the plain daa myself. Any ideas how it could be done? Kind regards Marc

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