Putting green firmness is one of the key performance characteristics that influence how challenging the greens will play on any given day. Like many other characteristics of a golf course, there can be tremendous variability in putting green firmness from course to course and even from day to day on the same course. The obvious factor affecting firmness is soil water content, but it is important to keep in mind that providing firm greens requires more than just reducing irrigation. The next most influential factors on putting green firmness are organic matter content and soil physical properties – i.e., gradation and angularity.
Soil Moisture
Soil moisture content is the most volatile of the factors impacting firmness and can result in rapid changes from day to day. If soil moisture is not precisely managed, firmness can even vary from green to green. That said, simply withholding irrigation for the sake of providing firmer greens is not always a good idea. Maintaining ultra-low soil moisture levels for more than a day or two during summer can lead to rapid turf loss. Adequate soil moisture levels and turf health must be taken into consideration to provide good conditions throughout the season.
Organic Matter
Soil organic matter plays a big role in putting green firmness as well. A putting green with excessive soil organic matter – i.e., thatch – will provide softer conditions than a putting green with ideal organic matter content. Truth be told, greens with excessive organic matter content rarely play firm, regardless of how much water is withheld. Organic matter acts like a sponge near the surface, so simply reducing irrigation will not provide the desired firmness in most cases. Organic matter management is critical if you want to achieve ideal putting green firmness. Although not as common, having too little organic matter can lead to unstable playing surfaces and have a negative impact on firmness and plant health.
Soil Physical Characteristics
The physical characteristics of the upper portion of the soil profile also have a significant impact on surface firmness. The uniformity coefficient (Cu) on soil tests and angularity of soil particles are of particular importance. These soil physical characteristics take time to modify from a turf maintenance standpoint. Topdressing sand selection, aeration practices and topdressing frequency should be carefully evaluated when attempting to modify these characteristics through cultural practices. During putting green construction, special attention should be given to these factors affecting firmness when selecting a rootzone mix.
Putting green firmness changes rapidly from day to day based on soil moisture content, but withholding irrigation can only do so much. Organic matter must be managed appropriately, and attention should also be given to the physical characteristics of topdressing sand. If you would like to have a more detailed conversation about putting green firmness at your course, contact your regional USGA agronomist.
Central Region Agronomists:
Paul Jacobs, agronomist – pjacobs@usga.org
Zach Nicoludis, agronomist – znicoludis@usga.org