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Iron chelate for plants | What is it and how does it work?

iron chelate
Written by Han van der Kooij Last update: 23-08-2022
Iron chelates are organic trace elements that bind the iron like a claw. In this way, iron remains available in the solution and thus available for the plant. A plant can only absorb nutrients dissolved in water. Iron fertilization is always dosed in chelated form. This, because iron easily precipitates when in contact with other elements. By adding iron to the solution through chelates, this will be prevented.

Types of chelated iron

Chelated iron are available in several types, all with their own characteristics. The most important difference is the strenght and therefore stability of the chelate. The strength of the chelate is depending heavily on the pH level of the solution, for example in the substrate mats or in the soil. As various pH values may occur in the root environment, we offer different iron chelates. There are three commonly used chelated irons in horticulture.

Chelate type 

Stability in relation to the pH 


Which iron chelate suits you best?

The stability of iron chelates is of upmost important for choosing iron chelate. If a chelated iron is not stable, it is not strong enough to hold on to the iron in the solution. At a pH level in which the chelate is not stable, the iron quickly precipitates, with the result that the plant isn't able to take in enough iron. The iron thas has been precipitated due to an incorrect pH level has become a 3-worthy iron, meaning a Fe² has become a Fe³. The disconnection of the chelate Fe³ cannot be reversed, since it has oxidized (known as chlorosis). Therefore, the selection of an appropriate chelate is of great importance. 

EDTA iron chelates

EDTA is the least strong ichelated iron on the market. EDTA iron chelates are mainly recommended for foliar fertigation, since they are not perceived stable enough to be added to a fertilizer tank. Besides EDTA, the HEDTA chelate has almost identical characteristics to the EDTA. 

DTPA iron chelates

DTPA chelates are used the most. This because most cultivations remain a pH below 6.5. The iron DTPA is therefore stable and available to the crops. Two liquid DPTA iron chelates can be distinguished: 3% and 6%. The two differ in terms of sodium used in production. The 3% DTPA chelate is produced with a large amount of sodium, while the 6% variant is mainly produced with ammonium. In various cultivations, sodium keeps adding up in time and is very likely to cause problems. To prevent these problems from occurring, the Iron DTPA 6% is often recommended. The only disadvantage of this DTPA 6% is the slightly higher cost of production, resulting in a higher cost price. 

EDDHA iron chelates

When the pH reaches a level around or above the 6.5, it is advisable to switch to the red iron, EDDHA (partly or completely). The EDDHA iron remains its stable to a pH level of over 10. EDDHA iron can be found on the market under several names. Even though, at first glance the characteristics may seem the same, the shape of the EDDHA chelate is extremely important. EDDHA chelates always consist out of a mixture of three different structures. The following figure gives an overview of the different shapes. 

How do chelates work?

Of the different EDDHA structures shown above, the top one is most stable. It’s called an ortho-ortho EDDHA. The other two types are called ortho-para and para-para EDDHA. Since all types of red iron (EDDHA) on the market contain one of the above-mentioned structures, it’s important to select the product with the highest ortho-ortho level.

  • Example:

    Take product A, an EDDHA chelate with 6% iron chelate of which 4% is ortho-ortho. This simply means that we are giving 4% stable iron chelate. This does not mean that the remaining 2% is not available to the plant at all, however, this will precipitate quickly, and its produced fruits/ vegetables will be much lower. If we now would replace product A with product B, an EDDHA chelate with 6% iron chelate of which only 2% is ortho-ortho, it means that the remaining 4% of iron chelate is less stable and will therefore precipitate quickly. The number of fruits or vegetables harvested is therefore much lower. Simply put, you will need about twice as much of product B than you would need from product A to get the same amount of iron to the plants. In practice, product B will therefore be offered more cheaply than product A. 

    What are the symptoms of iron deficiency

    Iron deficiency in plants manifests as mottled, yellowing leaves. In most cases, the younger leaves are affected first and symptoms will later spread to the rest of the plant. At some point, the entire leaf will turn pale and die. For some plants, the discolored leaves are the only indication that there is a problem. But for other plants, it can also cause, for example, growth retardation or falling fruit.
    You can also have the soil tested if you suspect an iron deficiency to make sure that an iron deficiency is present. Some plants are more susceptible to iron deficiencies. This is because the biology of each plant is different and so the ability to use and absorb iron differs from plant to plant.

Iron Chelates

Any questions about iron chelates?

Do you have any questions about crop care, chelated iron fertilizer, or do you want personal advice? Contact one of our product specialists, or use the form below. we will contact you within 24 hours on working days. 

Han van der KooijAbout Han van der Kooij

Han van der Kooij, fertiliser product specialist at Royal Brinkman, understands the customer like no one else. After being a grower himself, for 26 years, he knows the ropes and is aware of what is involved in being a grower. Converting his own knowledge and experience into recommendations that are useful to growers, is what he likes best about his job. "Finding that this leads to good results, makes me quite satisfied."

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