Correcting Problems With and From Iron Chelate Applications
March 5, 2026 A recent pair of e-Gro Alerts from W. Garrett Owen of The Ohio State University and Christopher J. Currey of Iowa State University looks at the application of iron chelate, concerning both its correct usage to treat iron chlorosis and how incorrect use can lead to phytotoxicity in plants. Here are a few insights from each piece:
Selecting and Applying Iron Chelates Correctly
Owen states that iron chlorosis “is one of the most persistent and economically frustrating micronutrient disorders in floriculture production.” This is because interveinal chlorosis often develops later in the crop cycle, presenting early uniform crops before displaying symptoms in the endgame. However, he says that the issue, most of the time, “is not a lack of iron in the fertilizer program, but a loss of iron availability as substrate pH increases and irrigation water alkalinity pushes iron out of solution.” Therefore, correcting this issue requires more than just adding additional iron into the mix. Owen stresses three important additional concerns to prioritize:
- Understanding root-zone chemistry.
- Selecting the appropriate iron chelate.
- Applying drenches or foliar sprays correctly.
Root-Zone pH and Alkalinity
For growers using soilless substrates, the availability of iron primarily relies on root-zone pH. According to Owen, “As pH rises, iron in solution rapidly converts to ferric iron, which reacts with hydroxides and carbonates and becomes insoluble.” Even small increases in substrate pH can make present iron insoluble, thereby creating the problem of iron deficiency (and its symptoms) in crops. Additionally, this increase in substrate pH is often due to the alkalinity of irrigation water, which can “vary widely by location and water source.”
In the event that soluble iron is limited, reduced, or becomes unavailable, chlorosis symptoms first appear in newly expanded leaves. From there, as iron deficiency worsens, “new growth can become very pale yellow or even bleached, and shoot growth slows, delaying canopy fill and finish.” At the identification of symptoms, troubleshooting is paramount, as trying to solve chlorosis without first verifying pH can lead to “repeated iron applications with uneven results.” If pH and alkalinity are determined to be at fault for iron solubility issues, selecting an iron chelate is the next step.
Phytotoxicity from Incorrect Iron Chelate Applications
Having visited a grower whose petunias and calibrachoa often suffer from chlorosis, and with iron chelate already having been applied unsuccessfully, Currey looks at why the treatment failed and covers the two best management practices for applying iron chelates:
- Understanding micronutrient requirements and substrate pH groups for crops.
- Thoroughly rinsing foliage after applying chelates.
Currey deduces that the reason why the onset of interveinal chlorosis in the grower’s crops was because the petunias and calibrachoa “are micronutrient inefficient plant species and require higher micronutrient concentrations in the rootzone compared to other crops to maintain green foliage,” and that the chelate was applied to all crops, instead of selectively.
However, in regards to the chelate specifically on the iron-deficient crops, Currey stresses the importance of following up applications with a rinse to remove chelate residue. Iron chelate residue “won’t just cause phytotoxicity in general micronutrient crops,” but “can also damage micronutrient-inefficient crops” with high iron requirements.
For additional information on iron chelate applications, including selecting the right type of chelate and additional corrective application methods, please read the full e-Gro (Electronic Grower Resources Online) alerts “Ironing Out Chlorosis: Selecting and Applying Iron Chelates Correctly” and “Phytotoxicity From Incorrect Iron Chelate Applications.”
Additional and current e-Gro alert pieces from Volume 15 (2026) can be found online.
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