HELPFUL HINTS HELPFUL HINTS
HELPFUL HINTS
FROM THE LAWN INSTITUTE FROM THE LAWN INSTITUTE
FROM THE LAWN INSTITUTE SHEDDING LIGHT ON SHADE
the light compensation point, or the point at which photosynthetic CO2
uptake exactly balances CO2 through respiration.
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 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. Te electromagnetic spectrum 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. 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.
Turfgrasses, like all plants, require sunlight in order to support photosynthesis, which literally means “synthesis using light.” As photosynthesis occurs, solar energy is used to drive the synthesis of carbohydrates and oxygen from carbon dioxide and water. In shaded environments, photosynthesis is reduced, which can result in decreased growth rates of turfgrasses, thinning, and even death. Tis is because plant survival dictates that net photosynthesis (carbon gains) exceed respiration (carbon losses) for the plant to continue to grow and store carbon. Te point at which this pendulum swings in either direction is called
Cool-season turfgrasses reach light saturation at approximately 50 percent of full sunlight, while warm- season turfgrasses typically require full sun to reach light saturation. Light intensity varies by location, diurnal cycle, time of year, atmospheric conditions, cloud cover, shade, etc. For example, during the spring months there can be 46 percent more PAR in the desert southwest than the northeast United States. When looking at it by month, PAR increases by 142 percent from January to August in Houston, Texas. Tese fluctuations by season and geographic location can impact which turfgrass species can be successful under shade.
Generally speaking, Fine fescue and Tall fescue offer the highest shade tolerance for cool-season lawns while St. Augustinegrass and Zoysiagrass provide the highest shade tolerance in warm-season turfgrasses. Within zoysiagrass varieties, additional research has shown that fine textured species that are often interspecific crosses of Z. japonica and Z. matrella or Z. pacifica typically have better shade tolerance than coarse textured varieties of Z. japonica.
It is important to remember that most, if not all, turfgrass species will perform best in full sun. Shade tolerance varies among species and cultivars and selecting the appropriate one for use is the first line of defense in managing healthy turfgrass in moderate to dense shade. Also, next time you see your shadow on the lawn remember that the particles of sunlight hitting your back just traveled 93 million miles only to be obstructed from hitting your turfgrass in the last few feet thanks to you!
release
For more information on lawn care and helpful “How to” tips, visit The Lawn Institute at:
www.TheLawnInstitute.org.
TPI Turf News July/August 2019 9
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