Turf Tips: What Makes A Lawn Grass O.K.

Volume X: Issue No. 2 Feb. 2012

In this issue: What makes a lawn grass  

Feature Story:  WHAT MAKES A LAWN GRASS  O.K. !

Last month we saw the “history of the lawn” . The lawn as we know it today developed as a monocot ground cover.  What we also saw was natural selection for “tolerance to low and frequent defoliation” by animal feeding pressure.  This is why turfgrass science started 100 years ago as an off-shoot of pasture management. So then, why does a “turfgrass plant” tolerate a mower, and pasture grass “grow back” after it’s been munched to the ground.

Well in the pasture grass sense, the plant must be able to grow back from basal shoots just above the ground level, and/or send up new shoots from the growing point (crown), using food reserves in the (emergency) regenerative process.  

For a “lawn grass”, the process is a little different.  If mowed properly, a lawn grass does not get shaved down to the nubs, as most pasture grasses do.  Instead, the  upper parts of the canopy are “clipped away”, in an even plane by a mechanical means.  What’s left is what is important, and what’s important is what’s left after the very last identical mechanical removal ! 

And here is why !  Think of a grass plant as a series of solar collector panels (leaves), on a mechanical pole (shoot), which elevate the solar collector panels to capture sunlight.  In order for the plant to be “efficient” in its ability to capture sunlight, the arrangement of width of the solar collectors, and the distance between the collectors on  the poles, as well and the concentration (shoot density) of the poles on the ground determine how much solar energy can be collected. That’s what a plant does best.  

So what makes a good “lawn grass”  based on the features of solar collectors, poles and pole density. 

If the solar collectors are wide, they need to be far apart on the poles, so they don’t shade themselves. Also in this case, the poles  need to be spaced farther apart on the ground (low shoot density), so the identical poles and the solar collectors next door don’t shade them, as well. 

When the solar collectors are narrow (fine leaf texture), the leaves can attach themselves closer together on the poles, and the result is more solar collectors on any given length of pole (short leaf internode leaf expression). As a result in this case, there can be more poles (shoots) in a square area, because less “shading” is taking place, because the narrow solar  collectors (leaves) produce  minimal shade.  The result of the combination of actual LEAF WIDTH,  LEAF INTERNODE DISTANCE,  AND SHOOT DENSITY produces a grass plant that when un-mowed, grows close to the ground.  We take advantage of this kind of growth by “selecting” plants with these favorable growth habits - - for use as mowed turfs.

The leaf width,  internode length and shoot density determines how low (the distance off the turf surface) that a grass plant can be clipped, without producing a stressed situation during re-growth.  That’s why we have turfgrasses that we use on golf greens that get mowed at 1/8” or less, and homeowner grasses which get mowed at 1 ½” (bermudagrass in the desert, and Kentucky bluegrass at high elevations), or at even higher heights such as 2.5 inches, or more (perennial ryegrass as winter overseed in low elevations, or tall fescue at medium to higher elevations).    

That’s what makes a lawn grass - - o.k. !

Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Jeff Silvertooth, Director, Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.  The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.