Lawn’s color can help you diagnose deficiencies

Any “weekend warrior” can tell you that the golden chalice of lawn care is to have the greenest lawn on the block. Weeds, insects and diseases are not a concern at this level as they just do not exist. However, after all the fertilizers have been spread, water has been applied and sweat has been shed, the possibility still exists that the grass is a dismal yellowlike tarnish on the world’s finest goblet. However, something can be done to turn that yellow grass to green. Here is what you need to know about treating iron chlorosis in the lawn:

Iron is necessary for chlorophyll production. Chlorophyll is the “stuff” that makes leaves green. Without iron, chlorophyll is not produced, so leaves turn pale yellow. Most gardeners are familiar with iron chlorosis in the landscape. Leaves of pin oak and sweetgum turn bright yellow while maintaining green veins. But few gardeners recognize the same symptoms as they appear on the lawn. A similar and sometimes mistaken condition is nitrogen chlorosis, or lack of nitrogen in the plant, leading to pale green leaves.

Begin by identifying the root of the problem. Iron chlorosis causes the turf to appear mottled with dark green grass interspersed with yellowish grass. A lack of nitrogen will cause the entire area to be yellow or pale green. When viewing individual plants, iron deficiencies appear first on the youngest leaves, while nitrogen deficiencies appear first on older leaves. When viewing the individual leaves, no nitrogen means no green color. A lack of iron appears as dark veins with lighter pale yellow between the veins. This is called interveinal chlorosis.

Iron chlorosis is not necessarily caused by a lack of iron in the soil, but rather, the plant’s inability to use the iron that is present. This could be caused by high soil pH (greater than 7.2), limited root activity as a result of overwatering or underaerating the soil or applying too much phosphorus that can bind with the iron to create products that are not usable by the plant.

The solution depends on the cause. During cool wet weather, roots can temporarily shut down, causing symptoms to occur. Usually when the rain stops, the roots start growing and plants have a full recovery. If the condition is brought on by lack of air movement into the soil or by overirrigation, turning off the water or having the lawn core-aerated can help solve the problem. If the cause is soil pH that is too high, the cure is not so simple. Foliar sprays of liquid iron may temporarily turn the yellow to green in as little as two days. However, the cure only lasts for three or four weeks before the pre-existing condition returns. Another, potentially longer, cure is to make granular applications of iron to the soil. The results are slow and varied. The final option is to change the soil pH. Although a very slow and tedious process, it is the one with the longest results. Begin by taking a soil test to determine the pH. Then begin applying sulfur at the rate of 5 pounds of sulfur per 1,000 square feet. Make applications in the early spring and fall until enough sulfur has been added to adequately adjust the soil pH. Pelletized sulfur is easier to work with. For best results, make the application after the lawn has been core-aerated, and water well.

– Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.