Everyone wants a thick, plush lawn. But some turf grasses, when left to their own devices or improperly maintained, can become too dense. This condition is known as thatch. Thatch is a problem because, if left untreated, it compromises the lawn's ability to absorb moisture and nutrients and can leave a lawn more susceptible to pests.
Between the green blades of grass you see on the surface and the soil underneath is a layer of living and dead organic material. This is known as thatch. It is made up of the stems and roots of the turf grass and becomes problematic when the material accumulates faster than it breaks down. Generally speaking, a layer of thatch that exceeds 1/2 inches thickness is considered excessive. This tightly woven layer is a favorable environment for pests, and leaves the lawn vulnerable to damage.
Some types of turf grass are more prone to thatch accumulation than others. However, lawn care practices can also exacerbate the problem. Over-watering and heavy use of nitrogen fertilizers are common culprits. These practices cause the roots and stems to grow too rapidly and outpace the decomposition of old matter. Thus, an accumulation of material and thickening of the thatch layer begins to occur. Contrary to popular belief, short lawn clippings do not contribute to thatch, as these are high in water content and break down rapidly.
Other factors can contribute to the thatch accumulation on a lawn, including the soil quality. Compacted soil can restrict root growth and development, and highly acidic soils slow down the process of decomposition of old roots and stems. Additionally, the use of pesticides that lessen the activity of microorganisms and earthworms can contribute to slow decomposition, and lead to thatch.
You can lessen the tendency of your turf to build up thatch in several ways. Apply nitrogen fertilizer in the fall rather than the spring. Fertilizing at this time of year doesn't result in the rapid, lush growth often seen with spring applications. Test the soil in your lawn before fertilizing to determine the proper amounts of nitrogen, phosphorous and potassium to apply. Also, mow your grass frequently so that the clippings left on the lawn aren't too long and bulky.
For serious cases of thatch, mechanical solutions like core aerification or vertical mowing may be warranted. Core aerification is a process in which a machine removes cores of soil from the lawn to improve drainage and air penetration. Many experts advise leaving the removed cores on the surface of the lawn to "top dress" the turf with the microorganisms found in the soil. Vertical mowing is also performed on heavily thatched lawns. These machines, also called power rakes, have steel blades or tines that dig into the turf, bringing some soil to the surface. This process leaves a great deal of debris on the lawn which must be removed.