There are several types of chelated iron available that characterize themselves with various features. The most important difference is the strength and therefore stability of the chelate. The strength of the chelate is highly dependent on the pH of the solution in which it is contained. As various pH values may occur in the root environment, we offer different iron chelates. There are three commonly used chelated irons in horticulture.

The stability of iron chelates is of utmost importance for choosing iron chelates. 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 that has been precipitated due to an incorrect pH level has become a trivalent 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 is the least strong chelated iron on the market. EDTA iron chelates are mainly recommended for foliar fertigation since they are not perceived as stable enough to be added to a fertilizer tank. Besides EDTA, the HEDTA chelate has almost identical characteristics to the EDTA.

DTPA chelates are used the most. This is 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. 

When the pH reaches a level around or above 6.5, it is advisable to switch to the red iron, EDDHA (partly or completely). The EDDHA iron remains 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 of a mixture of three different structures. The following figure gives an overview of the different shapes. 

Of the different EDDHA structures shown below, the top one is the 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.

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 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. 

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 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.

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