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For those looking to enhance their gardening skills, various extension educators will be teaching gardening classes on Thursdays at 7 p.m. Jan. 24 – Feb. 28. We will cover irrigation, pruning, fruit production, insect management, woody landscape plants and turfgrass management. To participate, contact the extension office at 852-1097. 

Over the next several articles we will be discussing how to manage iron chlorosis. Iron deficiencies are a common problem in our area. This isn’t because we don’t have iron but because it is often unavailable to plants due to elevated pH and the presence of lime in our soils. This can cause iron chlorosis. The primary symptom is a yellow leaf with a network of dark green veins. In severe cases, the entire leaf turns yellow or white and the outer edges may die. Yellow leaves indicate a lack of chlorophyll, the green pigment responsible for photosynthesis. A reduction in chlorophyll during the growing season can reduce plant growth and vigor. In addition, chlorotic plants often produce smaller fruits of poor quality. If iron chlorosis persists the plant may die.

pH is a measure of the acidity or alkalinity of a material. The pH scale ranges from 0 to 14, with 7 being neutral. A pH value below 7 indicates the soil is acidic, while values above 7 are alkaline. Most southern Idaho soils contain free lime, with related soil pH values ranging between 7.5 and 8.2. Our water is also often alkaline which makes long-term management difficult.

Iron chlorosis is known to be aggravated by cool soil temperatures, compaction, and water-saturated conditions. Chlorosis is often more severe where topsoil has been removed exposing the subsoil which is rich in free lime or calcium carbonates. 

First think prevention. Control of iron chlorosis is not easy and can be expensive. It is much better to select plants that are tolerant of high soil pH and less likely to be affected by low iron availability. Maples, aspen, raspberries, peaches, grapes, alfalfa, corn and potatoes are common plants in southeast Idaho that exhibit symptoms of iron chlorosis. You are more likely to get tolerant plant varieties through buying from informed local suppliers that know and offer adapted cultivars.

Second, don’t overwater. Excessive irrigation or poor drainage magnifies iron chlorosis problems. Plants in poorly drained areas are especially susceptible. This is particularly important in cold spring temperatures that decrease the availability of iron to growing plants. As the soil dries in the spring and temperatures rise, microorganism activity increases releasing natural iron available to growing plants. 

Third, warm the soil. Plant susceptible ornamentals on southern exposures to take advantage of warmer soil temperatures in the spring. Plastic mulches (clear, black, brown, or green) tend to increase soil temperatures and decrease spring chlorosis problems. 

Fourth, fertilize correctly. Improper fertilization can promote iron chlorosis. Applying too much nitrogen will stimulate excessive growth, which can cause plants to out-run their ability to take up iron. Likewise, excessive phosphorus can contribute to iron chlorosis by binding iron in the soil, by competing with iron for root uptake, or by binding up iron in plant tissues. Organic matter addition will temper iron chlorosis by increasing humic acid and feeding the soil microbes that release natural iron.

In future issues we will discuss treatment options. Iron management can be confusing. Not all iron products are in forms that work for plants. Not even all chelated iron products are equal and only certain types work in our environment. In the next issue we will tackle iron forms to help you spend money on what works.

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