Iron plays a significant role in maintaining tree health. It is a micronutrient involved in photosynthesis, respiration, and nitrogen metabolism. Despite its presence in most soils, iron can become unavailable to tree roots, leading to a common problem that affects tree vitality and growth.
Recognizing Iron Deficiency in Trees
Trees with iron deficiency often display chlorosis, a yellowing of the leaves. This yellowing typically occurs between the veins, while the veins themselves remain green, a pattern known as interveinal chlorosis. These symptoms are usually more pronounced on younger leaves or new growth.
Iron deficiency can also lead to stunted growth and reduced fruit production. Iron is a component of chlorophyll, the green pigment responsible for photosynthesis. Without sufficient iron, trees cannot produce enough chlorophyll, impairing their ability to capture sunlight and leading to a decline in health.
Understanding Chelated Iron
Chelated iron is iron bound to organic molecules, enhancing its solubility and availability for plant absorption. While iron is abundant in soil, it can become insoluble and difficult for trees to access, especially in high pH (alkaline) soils (generally above 7.0). In these conditions, iron binds tightly with other minerals, limiting its uptake by roots.
Chelation prevents this binding by wrapping around the iron ions, much like a “lobster claw,” keeping them from precipitating and making them accessible to the tree. This process ensures the iron remains readily absorbed by the plant, even in challenging soil environments. Chelated iron offers an advantage over non-chelated forms, providing a stable and available source of this micronutrient. This helps restore green color to leaves and improve overall growth.
Types and Application Methods of Chelated Iron
Several types of chelated iron compounds are available, with effectiveness varying by soil pH. FeEDDHA (ethylene diamine-N,N’-bis(2-hydroxyphenylacetic acid)) is particularly effective in high pH soil conditions, working well in a range from pH 4 to pH 10. Other common chelating agents include FeDTPA (diethylenetriaminepentaacetic acid) and FeEDTA (ethylenediaminetetraacetic acid), though these are generally less effective in soils with a pH above 7.2.
Chelated iron can be applied through various methods. Soil drenching involves dissolving the chelate in water and applying it to the soil around the base of the tree or in holes around the drip line. Foliar sprays involve applying the solution directly to the leaves, which can provide a quick, though often temporary, response. Trunk injections deliver the chelated iron directly into the tree’s vascular system, offering a more targeted and sometimes longer-lasting solution, especially for larger trees where foliar sprays are impractical.
Optimizing Chelated Iron Treatment
For effective chelated iron application, timing and dosage are important considerations. Treatments are often recommended in the spring before new growth begins. Following the specific dosage instructions on the product label is always recommended to prevent phytotoxicity, or plant damage, that can result from excessive application.
Soil testing is a beneficial step before applying chelated iron, as it helps determine the soil’s pH and existing nutrient levels, guiding the selection of the most appropriate chelate type. Beyond chelated iron application, maintaining overall tree health through proper watering practices and avoiding over-fertilization with other nutrients can also contribute to the tree’s ability to absorb and utilize iron effectively. While foliar sprays offer quick results, new growth may still show signs of chlorosis, indicating that repeated applications or a more sustained soil treatment might be necessary.