In a recent edition of The Pallet, a newsletter by the Turfgrass Producers of Texas, by Casey Reynolds, PhD., he explores the fundamentals of shade and its impacts on different turfgrass varieties, including St. Augustinegrass growth in shade.
Turfgrass Growth in Shade
Managing turfgrasses in shade can be one of the more challenging aspects encountered by turfgrass managers everywhere. Unlike weeds, insects or diseases, you can't simply spray something to correct it. Furthermore, who doesn't love a good shade tree on a hot summer day? Privacy fences, homes or other structures, trees, shrubs, etc. all have the capacity to block sunlight from reaching turfgrasses and thereby creating shade. In this edition of Rooted in Research, we'll explore the fundamentals behind shade, its impacts on turfgrass health, and recent research designed to determine exactly how much sunlight is needed to meet the needs of various turfgrass species. In order to understand shade, it's important to first understand the sunlight that it's blocking. Sunlight has properties of both particles and waves. Particles of light called photons contain energy that is delivered in various wavelengths which are defined by the distance between successive crests. The electromagnetic spectrum (Figure 1) includes the entire range of wavelengths of electromagnetic radiation delivered to the Earth's surface by the sun. Unfortunately, not all of these wavelengths are useful for plant growth. In fact, photosynthetically active radiation (PAR), which is what drives growth in plants, makes up a very small amount of this spectrum. The entire 300 nanometer (nm) range of PAR from 400-700 nm, when compared to the entire electromagnetic spectrum, is equivalent to the width of a coin (a United States dime) when compared to driving from New York, NY, to Los Angeles, CA. This tiny portion of light is all that's useful to plants. As a result, one can imagine that it doesn't take much additional shade from cloud cover, trees, homes, etc. to limit turfgrass growth in shade.