Brown Grass: by Tom Butzler

Typical lawn trying to recuperate from heat and drought. Photo courtesy of Nancy Bosold.

Driving around central Pennsylvania the past several weeks, I couldn’t help notice the amount of brown in many lawns. I’m not sure if it was dead or dormant but it was a very tough year for grass. The long extended temperatures and lack of timely rains put a lot of stress on our lawns, especially those areas facing south and west.

My colleague in southeastern Pennsylvania, Nancy Bosold, works extensively on turf and pointed out some interesting facts on grass and temperatures. Using some research from North Carolina State University, she noted that for cool season grasses, root growth is negligible at soil temperatures over 70 degrees, and stops at 77 degrees. During the summer, roots die off and thin out, and when hot soil temperatures inhibit re-growth the root system continues to weaken. Soil temperatures for the closest recorded site in central Pennsylvania, Rock Springs, were in the mid-70 degrees for much of July.

At this point in my harried life, I don’t put a lot of effort in maintaining my lawn other than mowing whatever is green and tall. While mowing my lawn this summer, I too noticed most of my grass looking brown except for the most beautiful stands of crabgrass. Whereas warm soil temperatures inhibit root growth on our cool season grasses, warm season grasses - like crabgrass, thrive in soil temperatures of 75 and 85 degrees.

Slopes, compacted or shallow soils, and proximity to hot surfaces all made matters worse. Photo courtesy of Nancy Bosold.

As noted by Bosold, the above ground temperatures didn’t help matters either. Shoot growth on our cool season grasses stop at 90 degrees. Looking at temperature data for the Williamsport area, most of July’s temperatures were over the 90 degree mark. Contrast that to warm season grasses (like our beloved crabgrass) where shoot growth stops at 120 degrees. It will have to get pretty darn hot for the crabgrass to die off in the summer.

In addition to air temperature on shoot growth, the hot-sunny weather was pulling moisture out of grass blades faster than the plants could replenish from the quickly drying soil.

Another stress factors Bosold mentioned were insects. Insect damage could also have pushed dormant turf over the edge. Populations of chinch bugs, sod webworms, and billbugs that wouldn’t normally cause a problem (or even be noticed) damaged lawns that were heat and drought stressed.

Renovations will be important this year because of the extensive damage. In a later column, I’ll talk about some steps that can be taken to get your yard back into shape.

Turf loss was extensive, here helped by compaction and disease. Photo courtesy of Nancy Bosold.