All plants need a balance of nutrients in the soil. Without these nutrients, they will fail to thrive and possibly die. While the amount of iron found in the soil is usually adequate, trees of all types occasionally develop iron deficiencies. Known as "iron chlorosis," this condition can be addressed with fertilization and pH adjustment of the soil.
Identification of Iron Chlorosis
Iron deficiency can be fairly easy to diagnose. It turns leaves yellow or yellowish-green, with bright green veins. In extreme conditions, the leaves can turn white. At first, it may affect only one part of the tree, but if not addressed, it can spread yearly until the entire tree is affected. If the condition is less serious, then a tree might show symptoms of chlorosis one year, but not the next.
Before fertilizing, check the pH of your soil. It's common that the soil will contain a good amount of iron, but that the high soil pH is inhibiting absorption. Also, watch out for overwatering, which causes symptoms of iron chlorosis. Using too much fertilizer can kill your trees, too. Pick slow-release or organic fertilizers for healthier trees.
Method: Foliar Sprays
The easiest way to fertilize your trees is to use a foliar spray. To make a foliar spray, purchase any commercially available fertilizer that contains iron chelates. Follow the manufacturer's instructions carefully to mix in the correct amount of water. Spray the mixture directly onto the affected leaves. You should notice results within a few days, but this is only a temporary correction. For more serious iron deficiencies, you should address the soil.
Method: Soil Incorporation
This fertilization method works more slowly, but the results are more lasting than leaf spraying. Calculate the area of your tree; you will need 2 to 3 lbs. of fertilizer per inch of trunk diameter. Dig small holes about 2 inches wide and 12 to 18 inches deep, every 2 feet along the perimeter of the tree's drip line (beneath its outermost branches). Holes should be angled toward the tree slightly and at least 3 feet from the trunk. Place fertilizer into each hole, fill in and water well.
Types of Fertilizers
The most immediately effective type of iron fertilizer is iron chelates. Chelates are most commonly used in foliar sprays, but can also be effective in the soil. They provide a supply of iron that is easily absorbed by a tree, regardless of soil pH. Iron sulfate and even sulfur are also commonly used to make soil more acidic, lowering pH and aiding in absorption. Iron sulfate is an effective fertilizer for soil incorporation.
- University of Minnesota: Tree Fertilization: A Guide for Fertilizing New and Established Trees in the Landscape
- University of Minnesota: Yard & Garden Brief: Iron Chlorosis
- North Dakota State University: Ag Extension: Fertilizing Trees
- University of California Co-Operative Extension, Davis: Fertilizing Temperate Tree Fruit and Nut Crops at Home
- Photo Credit tree image by jeancliclac from Fotolia.com
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