Why Iron Matters in Turfgrass

Iron is essential for chlorophyll synthesis, the green pigment that allows plants to photosynthesize. Without access to adequate amounts of iron, turfgrass leaves can become chlorotic, turning yellow and even white. Iron deficiencies commonly show up in the younger leaves. This condition is known as iron chlorosis. While the turf may still be growing, its appearance suffers, and over time, limited chlorophyll production can reduce overall plant health.Unlike nitrogen or potassium, iron is not very mobile within the plant, hence the symptoms appearing in newer foliage. This means it must be consistently available in the soil solution or applied directly to the foliage. The need for iron often increases in high-pH soils, during periods of rapid turf growth or under cool, wet conditions when root activity is reduced. So, is it just as simple as buying an iron-containing fertilizer and throwing it out in the yard? Not necessarily.

Heavy rates of foliar-applied iron applied during the heat of the day resulted in iron-toxicity on this creeping bentgrass putting green.

The Problem With Soil-Applied Iron Oxides

Many iron products available at garden centers contain iron oxide (Fe₂O₃ or Fe₃O₄), commonly known as rust. These forms are very stable in the soil and are, for all intents and purposes, unavailable to plants. When applied to your lawn, they may temporarily darken the soil surface or even stain sidewalks. Still, they do little to boost iron absorption or correct iron deficiencies in your grass. This is because iron oxide is not a plant-available form of iron; iron must be in a soluble form, such as Fe²⁺ (ferrous), to be plant-available. One analogy that works is thinking about our atmosphere being composed of approximately 78% nitrogen as N₂ gas; you’d think plants would never need nitrogen fertilizers, right? But N₂ is not a plant-available form of nitrogen. It’s the same theory as with iron in the soil, it needs to be plant-available.

Unfortunately, certain characteristics of Louisiana soils tend to promote iron oxidation into these unavailable forms or result in compromised root function and less iron uptake over time. Even when iron is applied in a soluble form, it rapidly converts to Fe³⁺ (ferric), which can form insoluble hydroxides and oxides, essentially locking away the nutrient. This soil chemistry is the primary reason why granular iron products or iron-rich composts often fail to improve turf color, even if they contain plenty of iron by weight.

Iron Oxidation in Soil

When iron is in the ferrous (Fe2+) state, it is soluble and available to plants. However, once exposed to oxygen in the soil, especially in well-aerated or high-pH environments, ferrous iron is quickly oxidized to ferric iron (Fe³+). Ferric iron precipitates as insoluble iron hydroxide (Fe(OH)₃), which turfgrass roots cannot take up.Several factors accelerate this process:

• High pH (>7.0): Increases iron oxidation and reduces solubility.
• High oxygen content: Well-aerated soils speed up conversion to unavailable forms. This is not very likely in the compacted, waterlogged soils common throughout the state.
• Low organic matter: Fewer natural chelators to keep iron soluble. This is more likely on new building sites where topsoil was stripped away.
• Excess phosphorus or calcium: These elements can bind with iron, making it less available.

Why Foliar Iron Applications Work Best

Due to the challenges associated with soil-applied iron, foliar feeding is the most efficient strategy for delivering iron to your lawn. Foliar iron treatments bypass the soil entirely, allowing the nutrient to be absorbed directly through the leaf cuticle and used almost immediately.

Chelated iron products, such as Fe-EDTA, Fe-EDDHA and Fe-DTPA, are especially effective in foliar sprays. These formulations keep iron in a soluble form long enough for the plant to absorb it. Liquid iron sulfate can also be used, although it may have a higher risk of leaf burn if applied at high rates or under hot conditions.

Visible results from a foliar iron application often appear within 24 to 48 hours as the turfgrass green-up intensifies. This response is not due to increased growth but to enhanced chlorophyll production. Foliar iron does not stimulate excess growth like nitrogen does, which makes it an excellent option during summer months when excessive growth could promote disease or require more mowing.

Best Practices for Applying Iron

When using iron on turfgrass in Louisiana, keep these practices in mind:

• Choose correct formulations: Chelated iron or iron sulfate solutions are most effective. If applying to soil, make sure to use a chelated form.
• Avoid granular oxide forms: These are largely unavailable and wasteful.
• Apply in the morning or evening: Cooler temperatures reduce the risk of leaf burn.
• Repeat as needed: Foliar iron benefits are temporary, typically lasting two to three weeks. No need to overdo it though.
• Watch for staining: Iron sprays can stain concrete surfaces — use caution around sidewalks and driveways.

Conclusion

Iron fertilization can be a great tool for improving turfgrass color and aesthetic appeal in Louisiana lawns. However, understanding how iron behaves in the soil — and why foliar applications are typically more effective — is essential for getting the desired results. By choosing foliar iron sprays and applying them strategically, you can achieve that lush, dark green lawn without promoting unwanted growth or wasting resources.