Iron is a micronutrient essential for healthy lawns, though required in smaller quantities compared to macronutrients like nitrogen, phosphorus, and potassium. Its application is often sought for its ability to produce rapid greening. Homeowners frequently turn to iron supplements to achieve a deep, rich color in their turf when standard fertilizers do not provide the desired aesthetic.
Iron’s Function in Lawn Vitality
Iron’s primary function in turfgrass is its role as a catalyst in the production of chlorophyll, the pigment responsible for the green color of plants. Although iron is not a part of the chlorophyll molecule itself, it is necessary for the biochemical pathway that synthesizes it. When iron is readily available, the turf can produce more chlorophyll, which translates to a darker, more desirable green hue, often described as a “green-up.”
This effect is distinct from the growth stimulated by nitrogen, which is responsible for increasing the overall biomass and height of the grass. Applying iron intensifies turf color without promoting excessive vertical growth or requiring increased mowing frequency. Furthermore, grass with adequate iron levels shows improved metabolic efficiency, enhancing its resistance to environmental stressors like heat, drought, and heavy foot traffic.
Recognizing Iron Deficiency in Turf
Iron deficiency, known as iron chlorosis, presents specific visual symptoms. The most common sign is the yellowing of the grass blade tissue between the veins, called interveinal chlorosis. This discoloration usually appears first on the newest growth, the upper leaves of the plant, because iron is an immobile nutrient within the grass structure.
In contrast, a nitrogen deficiency typically causes a more uniform, pale green or yellowing across the entire leaf blade, starting with the older, lower leaves. If iron chlorosis is severe, the affected leaves can turn almost white, and applying nitrogen fertilizer to an iron-deficient lawn can worsen the yellowing. Performing a soil test is the most definitive way to confirm an iron deficiency and understand the soil conditions, such as high pH, that might be causing it.
Choosing and Applying Iron Supplements
There are two primary forms of supplemental iron available: ferrous sulfate and chelated iron. Ferrous sulfate is an inorganic salt that provides a quick-acting source of iron. It is generally less expensive, but it can quickly become unavailable to the plant, especially in alkaline soils, because the ferrous iron (Fe²⁺) oxidizes into the plant-unavailable ferric form (Fe³⁺).
Chelated iron products bind the iron molecule with an organic compound, or chelate, which protects the iron from reacting with other soil elements. This protection makes the iron more stable and bioavailable, particularly in soils with a high pH (above 7.0), and the effects tend to last longer. Although chelated forms are more costly than ferrous sulfate, they offer a more sustainable correction for iron issues in challenging soil environments.
The application method also influences the speed and duration of the green-up. Liquid applications are sprayed directly onto the grass blades, allowing quick absorption through the foliage for rapid color results. Granular products, typically incorporated into a dry fertilizer blend, are applied to the soil for a slower release and longer-lasting effect. Foliar application is generally the most effective way to ensure the grass takes up the iron, especially when dealing with high-pH soil conditions.
Avoiding Common Application Hazards
One significant hazard associated with iron application is the risk of staining concrete, stone, or painted surfaces. Iron compounds, particularly when wet, react with these materials and leave persistent, rust-colored marks. To prevent this, sweep or blow any granular product off hard surfaces and back onto the lawn before watering. Liquid applications require care to ensure drift does not reach sidewalks or driveways.
In many cases, iron deficiency is caused not by a lack of iron in the soil but by the soil being too alkaline (high pH). When the soil pH is above the ideal range of 6.0 to 7.0 for most turfgrasses, the existing iron becomes unavailable for the grass roots to absorb. Applying iron without addressing the underlying high pH is only a temporary fix; soil amendments like sulfur may be needed for a long-term solution.
While rare, over-application of iron can lead to iron toxicity, manifesting as leaf burn or a dark green, black, or purplish discoloration of the grass. Excessive iron can also interfere with the uptake of other nutrients, such as phosphorus, magnesium, and zinc, leading to a nutrient imbalance that stunts growth. Adhering carefully to product label rates and using a soil test to guide application avoids these negative consequences.