Strength from the Ground Up: Measuring Sod Strength to Advance Turfgrass Research at Penn State

October 12, 2026 | Pennsylvania Turfgrass Council | PODCAST

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Welcome to The Turf Zone Podcast. This episode covers measuring sod strength to advance turfgrass research at Penn State. Written by Ava Veith, Zineb Alouani, Chase Straw and David Huff – Department of Plant Science, The Pennsylvania State University.

Why Sod Strength Matters

Long-term turfgrass stability is not controlled by a single factor, but rather by the interaction of turfgrass species, cultivar genetics, rootzone properties, and management practices. Turfgrass failure often becomes visible when the surface can no longer resist shear forces, whether during an athlete’s planting and pivoting movement, excessive divoting from golf play, or sod breaking apart during harvest and handling. In research plots, these weaknesses may appear as inconsistent performance from one area to another. Across athletic fields, golf courses, lawns, and sod farms alike, structural weakness limits turfgrass performance.

At the center of these issues is sod strength. Sod strength refers to the resistance of the turfgrass–rootzone system to tearing or shearing forces. It reflects how effectively roots and other plant structures reinforce the turfgrass-root system. In other words, sod strength represents the physical integrity created by the interaction between turfgrass biology and the soil beneath it.

Traditionally, turfgrass performance has been evaluated visually through percent cover, color, density, and recovery after wear. While those indicators are important, they do not directly measure structural stability. A surface may appear dense yet still lack strong structural integrity. Likewise, it may recover quickly but remain vulnerable to tearing under load. By directly quantifying structural integrity, objective measurements of sod strength allow turfgrass professionals to better connect turfgrass genetics, growth habits, and management practices with real-world durability.

Expanding Turfgrass Research with Penn State’s New Sod Strength Tester

With support from the Pennsylvania Turfgrass Council (PTC) Board of Directors, Penn State recently acquired a sod strength tester to expand its turfgrass research capacity. This equipment allows us to apply a controlled pulling force to turfgrass sod and directly measure the resistance of the turfgrass-rootzone system before tearing or shearing occurs.

Unlike visual ratings or indirect indicators of performance, the sod strength tester generates objective and repeatable measurements of turfgrass structural integrity. It quantifies how effectively the turfgrass-rootzone system resists separation under load and how the turfgrass canopy holds together under stress. These measurements help translate turfgrass biology into measurable performance data. With this tool, Penn State can now evaluate structural stability across a range of systems, including athletic fields, golf courses, lawns, and sod production. Ultimately, PTC’s investment strengthens our ability to evaluate how turfgrass species, cultivar genetics, and management practices influence measurable durability in real-world turfgrass systems.

Using the Sod Strength Tester in Turfgrass Research

Several factors influence sod strength. Turfgrass species differ in growth habit and lateral spread, while cultivar genetics affect stolon and rhizome production, tillering capacity, and root mass. Rootzone composition influences the structural integrity of the turfgrass-rootzone system and moisture dynamics, and management practices such as fertility, irrigation, mowing height, traffic intensity, and cultivation further shape how the turfgrass system develops and responds to stress. By measuring sod strength, researchers can evaluate how these interacting factors influence structural performance under real-world conditions.

At Penn State, the sod strength tester will be incorporated into multiple research initiatives led by faculty within the Department of Plant Science, including Dr. Chase Straw and Dr. David Huff. Across both cool- and warm-season turfgrass systems, this tool adds an objective measure of structural durability to traditional performance evaluations. By quantifying differences in resistance to tearing, it provides insight into structural integrity that may not be apparent through visual ratings alone. While cultivar evaluation is one important application, it represents only part of the sod strength tester’s broader research potential.

Beyond cultivar trials, the equipment can be used to compare management strategies and evaluate long-term turfgrass performance under traffic. For turfgrass managers, these measurements connect directly to outcomes that matter, including reduced divoting, improved surface stability, and better recovery following repeated stress. By integrating sod strength into our research programs, we can provide clearer guidance on how species selection, cultivar choice, and management decisions influence real-world durability. The following sections highlight two graduate research projects that demonstrate how the sod strength tester is being used to address practical challenges facing turfgrass managers.

Evaluating Kentucky Bluegrass Cultivar Mixtures for Athletic Field Durability

One of the first research applications of the sod strength tester will be within doctoral research conducted by Ava Veith, a Ph.D. student in Penn State’s Department of Plant Science under the advisement of Dr. Chase Straw. Her research focuses on athletic fields and how surface characteristics influence performance. Using the sod strength tester, she will compare Kentucky bluegrass cultivar mixtures to quantify differences in sod strength, recognizing that greater structural integrity and resistance to tearing are highly desirable for high-traffic athletic fields. Kentucky bluegrass remains a foundational species for many cool-season athletic fields due to its rhizomatous growth habit, strong recuperative potential, and ability to form a dense, uniform playing surface. Its capacity to spread laterally through rhizomes allows damaged areas to recover following traffic. However, not all Kentucky bluegrass cultivars express the same level of rhizome production or structural strength. Differences in rooting density, rhizome aggressiveness, and canopy structure can influence how well a surface resists divoting and tearing during athletic play.

This study centers on a new Kentucky bluegrass cultivar developed by Dr. David Huff that is believed to exhibit more aggressive
rhizome production. The experimental cultivar will be incorporated into mixtures at varying percentages alongside commercially available Kentucky bluegrass cultivars that are already widely used on athletic fields. By adjusting the proportion of the new cultivar within each mixture, the research aims to determine whether increasing the proportion of rhizome-aggressive genetics translates into measurable gains in sod strength.

For athletic fields, increasing sod strength is particularly desirable. Fields subjected to repeated cleat traffic must resist shear forces generated during cutting, pivoting, and acceleration. Greater sod strength can reduce divoting, improve surface stability, and help maintain more consistent footing across high-use areas. Even small improvements in structural integrity may influence how a field performs over the course of a season. Ultimately, this research will provide sports field managers with clearer guidance on selecting Kentucky bluegrass cultivar mixtures that maximize durability under high-traffic conditions.

Evaluating Cold-Tolerant Bermudagrass Cultivars for Structural Performance

In addition to cool-season turfgrass research, the sod strength tester will also support graduate research led by Zineb Alouani, a master’s student in Penn State’s Department of Plant Science under the supervision of Dr. Chase Straw. Her research focuses on evaluating cold-tolerant bermudagrass cultivars for potential use in the transition zone and northern environments.

Bermudagrass is widely used on athletic fields and golf courses in warmer climates due to its aggressive growth habit, excellent traffic tolerance, and ability to recover quickly from wear. However, cultivar performance can vary significantly, particularly when bermudagrass is grown outside of its traditional adaptation range. Cold tolerance, winter survival, and structural durability are key traits that influence whether a cultivar can perform reliably in cooler regions.

As part of this research, experimental cold-tolerant bermudagrass cultivars developed by Dr. Yanqi Wu at Oklahoma State University will first be established and propagated in greenhouse conditions before being transplanted into field research plots. Once established, the sod strength tester will be used to quantify differences in sod strength and structural integrity among cultivars. By measuring how strongly the turfgrass-rootzone system resists tearing forces, the equipment provides an objective way to evaluate structural performance beyond traditional visual ratings.

Integrating sod strength measurements into bermudagrass evaluation will help researchers better understand how differences in growth habit, rooting characteristics, rhizome development, and lateral spread influence turfgrass durability. Ultimately, this work will contribute to identifying cultivars that combine cold tolerance with the structural resilience required for high-traffic turfgrass systems in the transition zone and beyond.

Why This Matters for Pennsylvania Turfgrass Managers

For Pennsylvania turfgrass managers, this work aims to provide clearer, data-driven guidance. By incorporating sod strength measurements into ongoing research, Penn State can generate information that supports more confident decisions related to turfgrass species and cultivar selection. Rather than relying solely on appearance-based evaluations, managers will have access to objective performance data developed under Pennsylvania growing conditions.

Importantly, this research is made possible through the support of the PTC and its members. PTC’s investment in the sod strength tester strengthens the connection between industry needs and university research efforts. As studies progress, findings will be shared through extension programming, publications, and outreach efforts to ensure that results are returned directly to the PTC community.

The addition of this tool expands Penn State’s ability to address questions facing turfgrass managers while strengthening collaboration between university researchers and the turfgrass industry. Together, these efforts will help ensure that future research remains practical, regionally relevant, and focused on improving turfgrass performance across Pennsylvania.

Looking Ahead: Continued Collaboration in Turfgrass Research

The Pennsylvania Turfgrass Council Board of Directors and its members play an important role in supporting turfgrass research at Penn State. Investments such as the sod strength tester strengthen the connection between industry needs and university research while creating new opportunities to better understand turfgrass performance. As these research projects develop, the findings will be shared through extension programming, publications, and outreach efforts to ensure that new knowledge is returned directly to the turfgrass professionals who support this work. Continued collaboration between Penn State researchers and the PTC community will help ensure that future research remains practical, relevant, and beneficial for turfgrass managers across Pennsylvania. We sincerely appreciate PTC’s continued investment in turfgrass research at Penn State.

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