How Much Iron Does Grass Need?

Iron helps keep your lawn dark green.
Iron helps keep your lawn dark green. (Image: Comstock/Comstock/Getty Images)

With 5 percent of the earth's crust made of iron, you may question why iron needs to be applied to your lawn. A lawn's ability to use iron depends upon several factors and differs greatly due to grass variety and soil pH. Identifying iron chlorosis in your lawn will help you determine if iron application is necessary. How much and what type of iron to apply to your lawn can be answered by identifying your grass type and soil pH.

Iron Chlorosis vs. Nitrogen Deficiency

Iron is essential in the creation of chlorophyll, which in turn plays a key role in photosynthesis. A lawn suffering from iron chlorosis, or yellowing of the leaves, can be hard to distinguish from a nitrogen deficiency, which also appears as a yellowing of the leaves. Iron chlorosis can be diagnosed by five key symptoms. First, the yellowing may occur in spots or patchy blotches, whereas nitrogen deficiencies generally appear over a large area. Second, iron chlorsis displays a definite yellow color, and a lack of nitrogen is a light green. Thirdly, the yellowing of the leaves in iron starts out on the younger leaves and nitrogen on the older, lower leaves. The fourth symptom to diagnose iron chlorosis is growth rate. A lack of iron will not diminish growth rate, but nitrogen will. Last of all, an iron-deficient lawn will actually become worse if nitrogen is applied. If your lawn gets darker green after a nitrogen application, you know you have solved the problem.

Grass Type

Identifying what type of grass you have will help you determine how much iron to apply. Warm-season grasses like centipedegrass, bahligrass, bermudagrass, St. Austinegrass and zoysiagrass tend to be more sensitive to iron deficiencies. Cool-season grasses include ryegrass, bluegrass and fescue. Cool-season grasses in general are not as susceptible to iron chlorosis as warm-season grasses but can still have problems in soils with a high pH.

Soil Type

Even with an adequate amount of iron in the soil, if it is not in the right form, your grass will not be able to absorb it through its roots. Iron precipitates, or becomes a solid, in high pH soils. High pH soils, also known as alkaline soils, can be found in arid, desert regions of the country and at high elevations. If you grow a warm-season grass, such as bermudagrass in a high pH soil, you will need to apply more iron to your lawn than a homeowner who is growing a cool-season grass in an acidic soil.

Iron Fertilizers

Once you have identified that your lawn is suffering from iron chlorosis, you can make an iron application. There are several types of iron fertilizers available, and you should select one based upon your soil pH. Iron comes in granular or liquid form. If you have a high pH soil, a foliar application will avoid going through the soil and tying up the iron. There are granular forms of iron that are chelated to prevent the precipitation of iron in the soil and are appropriate for ground application. If you have a low pH, or acidic, soil, there are many granular iron formulations that will produce the dark green lawn of your dreams. Check with your local nursery staff to discuss what type of iron is right for your part of the country.

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