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When I buy iron supplements for my plants, is there a difference between "chelated iron" and "fully chelated iron"? I found one that doesn't say "fully", but it's half the price. Is there even a difference?

If you look at this one, it says "chelated iron". (look at the picture of the label) https://www.homedepot.com/p/Western-States-1-Gal-Vitamin-B-1-Liquid-Fertilizer-100047058/100607914

But this one is "fully chelated". (top right of the label) https://www.homedepot.com/p/Liquinox-1-Gal-Iron-and-Zinc-Fertilizer-100047053/202519329?MERCH=REC-_-rv_search_plp_rr--NA--202519329-_-N

NL3294
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    According the content, both have chelated iron, and only chelated iron. "The word "fully", like most of the names are simply marketing bullshit (like the B1 vitamin). – Giacomo Catenazzi Jul 25 '18 at 08:34

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The reason the second product is more expensive is that all the minerals mentioned are fully chelated, i.e. bound to EDTA. If only the iron is chelated, and the other minerals are not i.e. partially chelated, then the iron can disassociate from the EDTA and bind to another mineral forming an insoluble complex which is no longer available to the plant which means a waste of money.

And for the details, there are two ways plants respond to iron deficiency.

enter image description here

Figure 3: Strategy I and Strategy II mechanisms for iron uptake. A. Strategy I plants induce the activity of a proton ATPase, a ferric chelate reductase, and a ferrous iron transporter when faced with iron limitation. B. In contrast,Strategy II plants synthesize and secrete phytosiderophores (PS) into the soil in in response to iron deficiency. The PSs bind ferric iron with high affinity and the resulting PS-Fe3+ complexes are transported from the soil into the plant root.

Most plants adopt Strategy 1 which is why shops sell chelated iron, so that ferric chelate reductase released by the plant can allow it to be absorbed using the ferrous iron transporter enzyme.

https://uk.solufeed.com/knowledge/fully-chelated-the-devils-in-the-detail https://www.nature.com/scitable/knowledge/library/plant-soil-interactions-nutrient-uptake-105289112

Graham Chiu
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  • A doctor of botany told me that root hairs can produce enzymes, etc, that can solublize components that regular chemistry says are relatively insoluble. – blacksmith37 Jul 28 '18 at 20:26