 |
| Over thirty years of Verticutting experience. With Bermuda, Zoysia, Bahia and St. Augustine grasses |
 |
| The best way to control top growth, thatch and improve mowing |
MORE ABOUT THATCH Thatch and Its Control in Florida Lawns
By L.E. Trenholm, J.B. Unruh, and John L. Cisar
Thatch is defined as an intermingled layer of dead and living shoots, stems, and roots that develops between the zone of green vegetation and the soil surface. Thatch consists of a loosely interwoven collection of plant matter that leaves the turf feeling spongy or puffy (Figure 1). When excessive (1 inch or more), thatch causes serious problems in Florida lawns.
Footnotes
1.
This document is ENH12, one of a series of the Environmental Horticulture Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date September 16, 2001. Revised December 20, 2001 and June 30, 2006. Please visit the EDIS web site at http://edis.ifas.ufl.edu.
Why is Thatch a Problem?
Thatch accumulations are undesirable for a variety of reasons.
• Thatch can restrict water and air movement into the soil. Dry thatch tends to repel water rather than allow infiltration, and wet thatch enhances disease problems. If your lawn has dry spots that are difficult to rewet (unless you almost flood the areas), these are probably dry thatch spots.
• Thick thatch makes mowing very difficult. As thatch builds up, mowing height actually increases above the soil line, and the turf becomes very spongy, allowing the mower to sink into the turf and scalp the lawn. This results in an uneven appearance and often a mottled brown and green surface.
• Thatch provides an ideal habitat for insects and disease. Thatch accumulation is associated with an increased incidence of many insects and diseases.
• A thatchy condition elevates the growing points (crowns), runners (rhizomes and stolons) and roots above the soil surface. As a result, the lawn is prone to damage from mowing too low and from environmental stresses such as winter injury because elevated plant parts are exposed to greater extremes in temperature. Centipedegrass is especially sensitive to winter kill because the stolons are elevated and are more prone to cold temperatures in thatchy lawns. Heavily thatched lawns also go dormant following the first exposure to cold weather, and green-up more slowly in spring.
• Thatch can interrupt and restrict the downward movement of pesticides and fertilizers into soil. This reduces the effectiveness of these materials, making pest control difficult and producing a nonuniform, erratic response to fertilization.
Figure 2. Brown Patch: Certain diseases are more likely to prevail in thatchy lawns. It is also harder for chemicals to penetrate through thatch, making them less effective.
Figure 3. Sod Webworm: Many insects also favor thatch.
Causes of Thatch Buildup
Thatch is basically a residue problem that occurs in most turfgrasses. Thatch buildup has been attributed to numerous factors. Excessive plant growth (when vegetative production exceeds decay) results in the accumulation of thatch. Grasses depend upon constant regeneration for survival, and new growth of creeping grasses covers the old, causing residue accumulation.
St. Augustinegrass, hybrid bermudagrass, seashore paspalum, and zoysiagrass often accumulate excessive thatch. Likewise, improper management practices such as overfertilizing, overwatering, and infrequent mowing often increase thatch buildup. In addition, failure to keep the soil environment favorable for bacterial and fungal growth—by pH control, adequate irrigation, and aeration—decreases the rate of decomposition of thatch residues, because these organisms are responsible for decay of organic matter. Failure to remove clippings after mowing has been cited as a cause of thatch buildup, but research findings do not support this concept. If properly mowed, leaf clippings decompose readily and do not contribute to thatch.
Thatch Control
Effective control of thatch requires a combination of several management practices. These include reducing plant growth and increasing microbial decomposition, and periodically removing thatch by scalping and/or vertical mowing.
Cultural Practices
Excessive fertilizer and irrigation are two of the primary causes in thatch buildup over time. Fertilizer should be applied as necessary to maintain reasonable growth and density. This will minimize weed invasion. Excessive succulent growth caused by overfertilization increases thatch, increases susceptibility to pests, and reduces the turf's overall tolerance to environmental stresses. Mowing practices can help control thatch buildup. Lawns should always be mowed at the recommended height and frequency. Thatch seldom increases if no more than 1/3 of the leaf blade is removed at each mowing.
Liming of acid soils may help increase decomposition of thatch residues and thus retard buildup. A soil pH of 7.0 is ideal for maximum microbial activity and decomposition.
Mechanical Thatch Removal Scalping
Close mowing or scalping is a procedure where the turf is mowed to a much shorter height than normal in an attempt to remove thatch. We do not advise homeowners to attempt this without consulting a turfgrass professional or your county extension agent. Damage done to the lawn from scalping may kill St. Augustinegrass or centipedegrass and can severely injure other turf species.
Vertical Mowing
The most common method of mechanical thatch removal is the use of a heavy-duty vertical mower. This specialized piece of equipment has evenly spaced, knife-like blades, revolving perpendicularly to the turf, that slice into the thatch to mechanically remove it (Figure 2). This process removes both thatch and mat and simultaneously cultivates the soil and topdresses the turf ( not St. Augustine ). It is very important to use proper blade spacing when vertically mowing different turfgrasses. Use a blade spacing of one to two inches for bermudagrass and zoysiagrass, two to three inches for centipedegrass and three inches for bahiagrass and St. Augustinegrass. Because of their underground rhizomes, zoysiagrass, bermudagrass and bahiagrass may be vertically mowed down to soil level in several directions without killing the lawn. If all of the aboveground stolons are removed from centipedegrass and St. Augustinegrass, these turfgrasses may die. If thatch accumulation exceeds two to three inches, lawns should be vertically mowed carefully more than once, but the lawns should be allowed to fully recover between mowings.
Advantages of St Augustine grass
St Augustine grass makes a beautiful light green to dark green turf. It forms a dense turf that grows well in most soils throughout the south. It is used along the coastal ranges because of its good salt tolerance.
St Augustine also has good shade tolerance even under the beautiful live oak trees the south is so famous for. Great shade tolerance is one of the reasons it is preferred over bermudagrass. Bermudagrass has very poor shade tolerance and will only grow a couple feet into moderate to heavy shade.
The easiest way for establishment is by sod. It will give you an instant yard. The roots won’t take hold in the soil for a couple of weeks, so it will need to be watered carefully to keep from drying out. It can also be established from plugs and sprigs. Sprigs are stolons, often called, “runners”. Stolons are above ground stems that grow horizontally. The stolons will sprout and root at the nodes that form every few inches along it’s length. The daughter plants will be a clone of the mother plant. Once the stolon has securely rooted, you can cut the stolon and force the daughter plant to take on the role of a mother plant sending out more stolons. This will decrease the spread time.
St Augustine grass will go dormant when the soil temperatures fall below 55 degrees. If the soil remains warmer than 60 degrees all year, the grass will stay green. It will, however, slow in growth as the soil drops in temperature.
See: PLP - perfect lawn programs www.verticutting.com
More info: york.ysta@gmail.com
