The yellowing of plant leaves with green veins, known as interveinal chlorosis, often signals an iron deficiency. This problem is widespread in gardens with alkaline or high-pH soils, where iron is abundant but chemically inaccessible to plant roots. Chelation is a necessary chemical intervention that makes iron soluble and available for plant uptake. This guide provides practical instructions for creating a homemade chelated iron fertilizer to address this common issue.
Why Plants Need Chelated Iron
Iron is a micronutrient required for the synthesis of chlorophyll, the green pigment responsible for photosynthesis. Without sufficient iron, plants cannot produce the energy they need, leading to chlorosis, which first appears on the newest growth. The deficiency is usually due to the iron’s chemical form in an environment with a pH above 7.0, not a lack of iron in the soil itself.
In alkaline conditions, the readily absorbed iron ion (Fe2+) quickly reacts with oxygen and other minerals, converting into the insoluble ferric form (Fe3+). This conversion, called fixation, locks the iron into compounds the plant cannot absorb. Applying plain iron sulfate to high-pH soil offers only a temporary fix because the iron is rapidly rendered unavailable.
Chelation is the process where an organic molecule, known as a chelating agent, binds to the iron ion, forming a protective cage around it. This action keeps the iron soluble and prevents it from reacting with other soil components until it reaches the plant’s root hairs. The chelated iron remains available, allowing the plant to absorb the nutrient and resume healthy chlorophyll production.
Step-by-Step Guide to Making Homemade Chelated Iron
A simple and effective method for creating a liquid iron chelate involves combining ferrous sulfate (a common iron source) with citric acid (a readily available household chelating agent). Gather your materials: powdered ferrous sulfate, citric acid powder, clean water, and a non-metallic mixing container. Use distilled, rain, or reverse osmosis water, as tap water minerals can interfere with the chelation process.
The goal is to create a robust concentrate for later dilution. For an effective concentrate, dissolve three tablespoons of ferrous sulfate powder and one tablespoon of citric acid powder into one quart of clean water. This generous ratio ensures the iron is fully protected by the chelating agent.
First, carefully add the citric acid to the water and stir until dissolved; this slightly acidifies the solution, aiding chelation. Next, slowly introduce the ferrous sulfate powder while stirring continuously for several minutes. The solution should turn a clear, pale greenish-blue color, indicating the iron is in its soluble, chelated form.
If the solution immediately turns a cloudy orange or brown, the iron has oxidized and precipitated, meaning chelation was unsuccessful. This occurs if the water is too hard, the citric acid ratio was too low, or the iron source was already oxidized. If successful, allow the concentrate to sit for about ten minutes to ensure all solids have dissolved and the chelate complex has stabilized. Always wear gloves and protective eyewear when handling chemical powders, and work in a well-ventilated area.
Application Techniques and Storage
The homemade chelated iron concentrate is potent and must be diluted before application to prevent leaf burn or root toxicity. For foliar spraying, which offers the fastest correction of chlorosis, dilute the concentrate by mixing one part solution with ten parts water. Apply this spray directly to the leaves until fully coated, ensuring application is done in the early morning or late evening to prevent sun scorching.
For a systemic and longer-lasting treatment, a soil drench is the preferred method. Use a slightly less diluted solution: one part concentrate mixed with five parts water. Pour this mixture around the base of the plant, allowing it to soak into the root zone for absorption and transport throughout the plant.
The frequency depends on the severity of the deficiency. Foliar application can be repeated every two to three weeks until new growth appears green. A soil drench may only need to be applied once or twice per growing season. Since homemade chelated iron is less stable than commercial formulations, use the concentrate within two to three days of mixing, as the chelate bond will eventually break down.
Store any unused concentrate in a non-metallic, airtight container in a cool, dark location away from direct sunlight. Because the chelate bond inevitably breaks down, the solution loses effectiveness over time. Mixing smaller batches as needed is the most efficient practice to ensure maximum benefit for your chlorotic plants while minimizing waste.