U of G UPDATE
Thatch and Winter Hardiness – More Related than You Might Think
A
s the 2011 season is drawing to a close, many of you are preparing or have already prepared your turf for the winter ahead. Winter preparation is such an important part of turfgrass maintenance here in Canada and can mean the difference between a good season and a really bad one come spring and summer. Pam Charbonneau of OMAFRA does a great job of putting together tips and ideas for winter preparation so I will not get into methods in this article. Instead I will discuss one of the factors that can affect how well your turf survives a harsh winter, as well as how quickly it is able to green up in the spring; your thatch levels. I am confident that everyone reading this article is well aware of the negative issues that can arise from an excessive thatch layer, yet I would argue that many of you may not deem it important enough to fix the problem – especially at the risk of reducing the turf quality and playability even for only a week or so. The purpose of this article is to discuss excess thatch within the context of how it affects winter hardiness as well as to go over some remediation methods based on results from a four-year study that we have just completed at the Guelph Turfgrass Institute (GTI). Excess thatch and mat (organic matter intermingled with soil) can reduce winter hardiness in a number of ways. First and foremost, soil protects the crown and roots of the plant from extreme temperature shifts such that rapid freezing events in the fall are less likely to harm a plant surrounded by soil. Thatch and organic matter have much larger pore spaces than soil alone and therefore are less likely to buffer extremes in temperatures, making the plant more vulnerable to sudden shifts such as freeze events. This is especially important in the fall, if rapid decreases in temperature occur before the plant has had a chance to harden off. It is also important in the spring, when freezethaw events are most likely to occur and a buffered plant is going to be more protected than one anchored by thatch. Another issue that can arise from having excess thatch layers is the development of a shallow root system. Because the pore spaces in thatch layers are quite large, the roots are able to grow more easily within that layer and often will not penetrate the soil layers below. This is primarily an issue in the summer months, especially in uncharacteristically warm years like 2010 and this past season, as a shallow root system does not allow for access to moisture deep in the soil profile. ...continued on page 20
Figure 1. Effect of weekly topdressing application on thatch-mat depth from the start of the study (2007) toward the end (2010). * Denotes a significant difference between treatments
Figure 2. Proportion of organic matter in the top 2.5 cm vs. the bottom 2.5 cm between plots that had weekly topdressing applied and those that had none.
Figure 3. Effect of weekly topdressing application on thatch-mat layer over time. Plot 403 had topdressing applied while 404 did not. Fall 2011 • Green is Beautiful 19