Chelated Iron: What Is it & How Do You Use It In The Garden

Iron is an essential nutrient needed by plants to function. Chelated iron like this is water soluble iron supplements plants can easily use. But we’re getting ahead of ourselves.

Iron is used up in some of the most vital functions of plants, such as:

  • Chlorophyll and enzyme production
  • Nitrogen fixation
  • Metabolism and development

For this reason, plants simply cannot function as they should without the presence of iron or iron supplementation.

chelated iron

Iron deficiency in plants can be spotted with a yellowing of leaves, usually between the dark green veins, which gives the leaf a spidery look.

This commonly referred to as lime chlorosis or iron chlorosis. With time, the leaves appear whitish, and start to die; resulting in a stunted growth of the entire plant.

This can be quite frustrating to a gardener, especially with the unsightly yellow or whitish leaves. Chelated iron is your best bet when treating iron chlorosis.

What Is Chelated Iron?

This is a soluble iron complex, primarily designed to make iron soluble in water for use in agricultural purposes.

In most cases, it comes as a darkish brown powder, and it can potentially be a mild irritant to the skin, eyes, and the respiratory membranes depending on the person.

A chelated iron fertilizer is one of the most popular and efficient methods of treating chlorosis.

In horticulture, chelated iron fertilizer is referred to as sequestered iron and serves as a plant tonic, where its mixed with other plant food products and nutrients.

For those who practice ornamental horticulture, iron chelate is widely recommended to feed plants such as Rhododendrons when the soil is calcareous.

Causes of Iron Chlorosis

Iron deficiency in plants is rarely caused by lack of iron in soil, because it is typically abundant in soil.

However, a variety of soil conditions may restrict the ability of a plant to get iron from the soil. Here are some of the causes of iron chlorosis:

  • Too much clay in the soil
  • A very high pH for the soil
  • High phosphorous content in the soil
  • Overly wet or compacted soil

The first step in diagnosing chlorosis is by performing a soil test. Your local agricultural extension center should help with this.

Keep in mind that they can also test leaf samples to determine exactly what nutrient or mineral is missing.

Although you may find out that your soil lacks iron, the problem could be from the one of the causes listed above.

Iron deficiency of Hydrangea macrophylla leaf - Iron chlorosis

Iron deficiency of Hydrangea macrophylla leaf – Iron chlorosis

Managing Iron Chlorosis

After iron deficiency is diagnosed, you can treat it by applying an iron foliar spray. But always remember that the best solution is prevention.

In this case, you should determine the underlying cause of the deficiency, and focus on treating it so you prevent the same problem from occurring later.

Evaluating the different causes of iron deficiency and correcting them can save you a lot of time and money spent on unnecessary and ineffective iron applications.

In general, iron can be applied in chelated form or as a ferrous sulfate. Ferrous sulfate or ferric iron is comprised of about 20% iron. It’s quite an inexpensive fertilizer, mainly used in foliar spraying.

In pH of above 7.0, it can be ineffective when applied to the soil, since iron will quickly transform to Fe3, which precipitates as iron oxides do.

Iron chelates are much better because the compound has stabilized iron ions, ideally preventing it from oxidizing and in turn precipitating away. The chelates contain three components in their formula:

  • Fe3 ions
  • Ammonium (NH4 ) or Sodium (Na ) ions
  • A complex like DTPA, EDTA, EDDHA, citric acid, amino acid, or humic-fulvic acid

In essence, different iron chelators will hold different strength depending on the given pH levels.

Moreover, they differ in their vulnerability to iron ions replacement by other competitive ions. At high concentrations, magnesium or calcium ions can replace the iron ions in the chelate.

Iron EDTA chelate: This compound is stable at a pH of below 6.0, and at levels above 6.5, almost 50% of the iron will be unavailable. This means that this chelate will be ineffective in alkaline soils.

Additionally, this chelate has a high affinity for calcium, and it should not be used in soils (or water) rich in calcium.

Iron DTPA chelate: Stable in pH levels of below 7.0. It’s also not as vulnerable to iron replacement by calcium as the ETDA.

Iron EDDHA chelate: usually stable at pH levels up to 11.0. however, it’s one of the most expensive chelates available.

Be sure to use chelates during spring, before growth starts. Sprinkle some dry chelated iron on the soil and irrigate, or dissolve in water and apply the chelated liquid iron around the base of the plants.

Iron chelates can also be applied in the holes surrounding the drip line of the affected plants.