Sod’s tricky transition

The physical and chemical differences in the sod-based soil vs. the root zone on which that sod is laid can cause issues.


Changing locations in life sometimes works great, and on other occasions, it can be a struggle. Perhaps you’ve spent years in an environment that you’ve grown used to, and then suddenly you move to a new area. It may take weeks, months or years for that to feel like home.

Grass can follow the same protocol. Sod grown in a specific climate on a given soil may appear happy and beautiful at the grower. After harvest, delivery and installation at a new site, it may fit in well immediately, or it could begin to struggle over time. However, with turf it isn’t a mental issue like it is with people. Instead, it’s often the soil type at the grower or the potential length of time it was at the sod producer and accumulation of thatch.

This is a common issue when grasses are grown on fine-textured soil and then delivered and laid on sand-based putting greens or athletic fields. The physical and chemical differences in the sod-based soil vs. the root zone on which that sod is laid can cause issues. Fine-textured soil retains more water and nutrients, which may encourage roots to stay in that area rather than penetrate the new soil below.

In addition, the physical differences — fine texture over coarse — also result in a “perched water table,” which we’re familiar with regarding USGA putting green construction. Water moves through the finer-textured layer and then backs up once it reaches the coarser-textured layer below. It doesn’t move into that coarse layer until saturation of the overlying layer occurs. The perched water table may encourage roots to stay up in the sod layer.

Thatch can cause similar issues. When excessive thatch accumulates, roots often tend to be happy in it. Thatch has a lot of porosity, and roots will grow extensively in a thatch layer if enough water is delivered. Bob Carrow, Ph.D., highlighted the impact of thatch in sod on the potential rooting effects after it’s laid in a GCM article (“Understanding layered and compacted soils,” in the February 1992 issue).

“Sometimes roots growing through sand or thatch may encounter a fine-textured soil that they would normally penetrate,” he wrote in that article. “However, if the sand or thatch offers less resistance and adequate water, roots may not develop into the underlying soil. Zoysiagrass roots often do this when excessive thatch develops.”

This suggests that sod producers should be aware of thatch in rhizomatous and stoloniferous grasses, which are those most likely to exhibit accumulation. Thatch can accumulate more with higher nitrogen levels, irrigation amounts and mowing heights. In addition, those receiving sod should check the level of thatch at the time it’s received.

Encouraging sod grown on fine-texture soil or sod that has accumulated excessive thatch to fit in its new location can be done over time with core aerification. If sod with a fine-textured soil is laid on a sand-based root zone, removing cores after aerification is important. Then, topdressing periodically with material equivalent to the root zone below will help make that profile more consistent over time.

If core aerification is done on sod that has accumulated thatch and is laid on something other than a sand-based root zone, leaving the cores on the surface to dry and then breaking them up is helpful. The soil from the cores will filter back into the thatch layer and help reduce the level of organic matter over time. Over the last three years, we have learned that zoysiagrass sod that had accumulated thatch in the surface inch has exhibited a significant decline in organic matter after a single annual core aerification at a moderate intensity.

If laying sod on a sand-based root zone, be aware of the soil texture on which it’s being grown. Sand-to-sand is generally a better match. Check sod that goes on all soil for levels of thatch. If more than a half inch of thatch is present, make plans to help reduce that level over time.

Moving turf from one location to another can be difficult, just as it can be difficult when we move from one area to another.

Jack Fry, Ph.D., is a professor of turfgrass science at Kansas State University, currently working at the school’s Research and Extension Center in Olathe, Kan. He is a 26-year member of GCSAA and was recently awarded GCSAA’s Outstanding Contribution Award for 2022.