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Shade Tolerance

Face the facts.  There is no turf that is 100% shade tolerant, meaning turfgrass will not grow in a “dense”, “full” or “heavy” shaded area.  It just does not exist.  All plants need at least some sunlight in order to flourish.  There are some “high speed” hybrids out there. Genetically engineered turfgrass. Yes; only in America.  Like turfgrass made in a test tube or something. 
Some “dense shade” seeds say on the bag that you have to have at least 3 hours of sunlight.  Is that dense or full shade then?  Full shade and full sun are easy to define.  Full shade basically means that the shade lasts all day long.  Very little or no direct sunlight hits the plant at any time of the day.  Full sun is just the opposite.  That means the sun hits the area all day long.  These other terms (dense, full, heavy, partial) are sometimes more difficult to define.  It depends on who you talk to.
I have seen where they say at least 25% of all existing turf is growing under some degree of shade.  Understanding the shade environment is critical to mission success in this situation.  Now, I may say some blasphemous things for us turf lovers in this blog post, but, I think you all now know for certain where my loyalty lies.  Yet, as I’ve said in a recent blog post, I also believe that one can achieve concord with one’s turf, trees and shrubs.  It’s a give and take, a balance.  Sometimes it’s more like walking a tightrope. 
Growing anything in the shade is tough. Restricted light inhibits carbohydrate production…the primary process of photosynthesis.  Without adequate carbohydrate production, plant health and vigor decline.  Even if SOME light penetrates a shade canopy, that light can be altered.  The leaves of the trees can intercept the light.  What light does penetrate the shade canopy can be of inferior quality.
One consideration is tree roots.  Where I live in northern Virginia the trees are huge and the tree roots are huge too.  Not only do these tree roots provide a serious hazard to mowing, if they are above the surface, they also compete with turfgrass for resources (water & nutrients).  I have some trees on my property that are at least 100 feet tall or more.  At chest height, the trunk diameters are two to three feet, some in the area are even larger.  It is important to remember that the root system of the tree can go as far out as the “drip line”.  A tree drip line is the area defined by the outermost circumference of a tree canopy where water drips from and onto the ground.  That is the minimum radial spread of a root system.  Some species of trees have root systems that are 1.5 to 2.0 times their heights.  Therefore, the competition for resources can spread far beyond the shaded area.  I have also read in some journals that certain species of trees may have roots that exude substances toxic to turfgrass. I will get into some more detail about tree roots in my next blog post.
What are some of the other factors in the shade?  Well, without certain levels of direct sunlight, soil and air temperatures can be 15 to 20 degrees (F) cooler than adjacent areas.  Wind movement may be restricted.  This can produce temperature and humidity layers in the shaded area.  The layering of humidity and temperatures, along with reduced air movement, may allow moisture to remain in the shaded area.  Remnant moisture can increase the chance of disease development.
What can we do, what management practices can we implement to improve shade tolerance?  As I’ve stated in so many blog posts before…species selection.  Which turfs tolerate shade better?  Note that I am NOT saying, which species can grow in the dark. 
Here is the order (from most tolerant to least tolerant of shade) of turfgrasses for warmer regions of CONUS:
Saint Augustinegrass
Saint Augustinegrass would be great because it can handle up to about 70% shade.  But, it has lousy cold weather tolerance…and shade can make things fairly cool.  And, I probably would not list Bermudagrass.  Its lousy without almost full sun.
But, you read in the first paragraph of this post how I talked (joked, really) about certain hybrids.  There are some Bermudagrass hybrids that have been developed to grow better in shade.  One of those cultivars is TIFGREEN.  Some others are TIFGRAND, TIFWAY, andTIFEAGLE.  These can do well in 60% to 70% shade…or maybe 5 hours a day.  (Still not 100%!)  Don’t get your hopes too high.  There are very few growers of these hybrids and these are really only for athletic fields and golf courses.  There are not too many private residences that have these hybrids in their yards.
There are many other Bermudagrass hybrids; like PATRIOT, LATITUDE, RIVIERA, YUKON.  But the ones above are the ones that are geared towards shade tolerance.
Zoysia and centipedegrass do okay.  OAKLAWN and TIFBLAIR are some centipedegrass hybrids.  Zoysia is good where low temperatures are a concern. 
In the cool regions, the order (from most to least tolerant) of shade tolerance turfs are:
Rough Bluegrass
Some cultivars of Kentucky Bluegrass, Tall Fescue and Perennial Ryegrass
As with any recommendations, you need to know the capabilities and limitations of each.  The fine fescues are good but the area needs to be cool and dry.  Bentgrass requires lots of maintenance.  Kentucky bluegrass has many hybrids that work; BIRKA, GLADE, NUGGET and BRISTOL, to name a few of the 36 or so.  Mixing Kentucky bluegrass with a fescue can also work for shady, dry areas.  Rough bluegrass is good for cool, wet conditions.  Ryegrass would have to be re-seeded each year.
So, that covers the species selection.  What about the management principles to help the turf tolerate shade?  If you’ve read my blog before, none of these actions should be a complete surprise.  For the same reason you should cut high, as I’ve recommended before, you should cut high in the shade.  You want to maximize the area of the turfgrass leaves to sunlight for photosynthesis.  My irrigation recommendations also remain the same; water in the morning, deeply and infrequently.  Avoid too much nitrogen fertilizing.  Use about half as much, or less, than you would use in your areas that have full sunlight.  In addition, keep an eye out for any disease.  Disease loves shaded, damp areas.  Keep a look out for powdery mildew or leaf spot.
Turf under lots of shade will NEVER be really thick and verdant.  If you are seeking absolute victory in this battle, you better be ready to withdraw and hopefully live to fight another day.  If you decide to withdraw, perhaps other ground covers may be the way to go.  Myrtle, English Ivy, Asiatic Jasmine, Creeping Fig, Ajuga, or Pachysandra might meet the requirement.  Keeping it green and aesthetically pleasing is still a victory.  I know it only too well…these are tough decisions.

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