What Is Thatch?
Thatch is not bad by definition. It is the layer of living and dead tissue between the grass leaves and soil surface. A thin layer of thatch, about ½-inch or less, protects the vulnerable crowns of grass plants from injury and improves the wear tolerance of turf. Without a thin layer of thatch, some types of grass wouldn’t tolerate regular foot traffic. It’s when the thatch layer builds up too much that it becomes a problem.
In just-right conditions, roots, shoots, and leaves grow, occasionally die, and then decompose in a regular rhythm that contributes to the overall well-being of the lawn. When the decomposition part of the life cycle is disrupted, thatch begins to build up. Spotting excessive thatch buildup before it becomes a breeding ground for lawn diseases and pests can help you save time and money on struggling grass.
1. Spongy Lawn
Walk across your lawn. If it feels squishy with each step, thatch buildup might be excessive. The dead stems, roots, and plant crowns that make up thatch pile up above the soil surface, creating the spongy texture above the more solid soil.
Some types of turfgrass create more thatch than others. Cool-season grasses prone to thatch buildup include Kentucky bluegrass, creeping red fescue, and creeping bentgrass. Thatch-prone warm-season grasses include Bermudagrass, zoysiagrass, and buffalograss. If your lawn is made up of one of these high-thatch turfs and it feels spongy when you walk across it, it may need to be dethatched soon.
Mechanical lawn aerator
2. Thatch Layer Is Too Thick
Lift a core of turf out of the lawn with a sharp spade. Using a ruler, measure the distance between the soil surface and the start of the green leaf tissue. This measurement is the amount of thatch buildup.
Lawns with more than ½ inch of thatch generally need dethatching. The more thatch that accumulates, the more unlikely it is to naturally decompose. A thick layer of thatch restricts air and water movement and can impede beneficial organisms that will naturally break down a thatch layer.
Don’t wait to remove excessive thatch; researchers have found that it is very difficult to remove a thatch layer exceeding 2 inches without extensively damaging the turf.
3. Frequent Scalping When Mowing
Mower scalping is a common problem on high thatch lawns. The mower wheels sink into the thick layer of thatch, allowing the mower deck and blades to ride on top of the turf. The low-riding blades cut the grass excessively short, resulting in a scalped lawn. The problem is amplified because the crown, or growth point, of grass plants grows on top of the thatch layer, making the plants even more susceptible to damage.
Thick thatch is not the only cause of scalping. Uneven terrain and insufficient mower height can result in scalping. A lawn with an overly thick layer of thatch will have consistent scalping across the surface, plus a spongy texture underfoot.
4. Pest Problems Don’t Respond to Treatments
A lawn with a thick thatch layer is more susceptible to pest problems. In time, grass plants growing below thick thatch move out of the soil below the thatch and begin rooting in nutrient-poor, dry, and generally stressful growing conditions caused by thatch. With limited water and nutrient access, pests can easily take hold of the weak plants.
Traditional remedies for control yield few, if any, positive results on a lawn with thick thatch. The already-compromised plants don’t bounce back even when the pest is controlled. Before choosing a control method for a pest problem, always check the thatch layer first. In many cases, removing a thick thatch layer will revive the grass, and then the turf will naturally overcome the pest problem.
