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
Centipedegrass
Zoysiagrass
Bahiagrass
Bermudagrass
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:
FineFescue
Bentgrass
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.
One big difference between heat stress and cold stress is cold stress can have an impact on warm season turfs AND cool season turfs. Whereas heat really only affects cool season turfs. Warm season turfs usually thrive in warm weather. As logic might dictate, cool season grasses are a little more tolerant of cold temperatures than warm season grasses.
As I’ve said many times in this blog, you got to select the species that is best adapted for the region you are growing the grass. That is not only the turfgrass adaptation zones (See my blog post on: “Turfgrass Adaptation”), but it also means the immediate environment…your yard…your playing field. Is there poor drainage? Is there lots of shade? Is there only direct sunlight? What is the annual or seasonal rainfall? What is the use of the stand or area – high use or low use? You have to look at all sorts of issues.
I will list below the cool season turfgrasses that are most tolerant to the least tolerant of cold stress:
Rough Bluegrass
Creeping Bentgrass
Kentucky Bluegrass
Annual Bluegrass
Tall Fescue
Perennial Ryegrass
Annual Ryegrass
The warm season turfgrasses most tolerant to least tolerant of cold are:
Zoysiagrass
Buffalograss
Bermudagrass
Bahiagrass
Centipedegrass
Carpetgrass
Saint Augustinegrass
As I mentioned earlier, drainage is important. Drainage is even more important in the case of cold tolerance. Okay; it is bad to have your turf submerged for long periods of time. Now, imagine your turf not only submerged but that water also freezes. And, it is a nice long, deep freeze. Not good. Keeping turf excessively wet or frozen is a primary reason for cold weather kill.
You need to ensure not only surface drainage but also subsurface drainage. Both of these considerations are directly linked to the “type” of soil you have. What percentages of sand, silt and clay do you have? Sand is porous; clay is not very porous. What this means is you may have to do some civil engineering on your property. You may need to change grades, install drains (french drain, perimeter drain, filter drain, collector drain, interceptor drain, fin drain, weeping tile, blind drain, rubble drain, rock drain); that sort of thing. That usually involves digging, laying of sand or gravel; maybe even some landscape fabric and installing some sort of pipes and/or grates/basins. This is not an inexpensive endeavor. And, do us all a favor, if you do this yourself; call Miss Utility before you even think about touching a shovel.
Judicious use of nitrogen fertilizers also applies here. I’ve written about getting a soil test to find out your requirements, seasonal or monthly applications, etc. In the past, my discussions about nitrogen fertilizers have been regarding its affect on the environment. Well, in this case, excessive late season applications of nitrogen can increase the lusciousness of the turf. That’s very nice, but it makes your turf more vulnerable to disease. And, if the turf is too succulent, it will be more susceptible to low temperature stress as well.
Also, with regard to fertilizer, maintaining adequate phosphorous and potassium levels is important. Potassium is especially critical to ensure cold weather tolerance. Some studies have shown that the balance or ratio between NP & K is very important. Cool season grasses show good cold hardiness if the N to K ratio is about 2:1 or 3:1. Warm season grasses should be fertilized in late fall with something like a 4-1-6 NPK ratio for good cold weather tolerance.
Finally, more topics I’ve already laid out for you – mowing high and maintaining a low level of thatch also help with cold weather hardiness. Mowing high increases photosynthesis capability and helps grow deep roots. While reducing thatch helps the soil surface dry out better and you won't have that moist layer remaining cold and have that layer freeze.
Next, I will get into shade tolerance. This also goes back to my earlier topic where I discussed “turf or trees” in my “Heat Tolerance” blog post.
Here in the CONUS turfgrass transition zone (See my blog post on “Turfgrass Adaptation”.) the conditions are lousy for cool season turf and warm season turf. It gets cold enough in the winter so warm season turfs go dormant. And it gets hot enough in the summer so cool season turfs go dormant. Its really NOT ideal for either type of turfgrass. Living in the north, deep south or out west makes turfgrass cultivation and care a little easier.
This is the time of year when I get a lot of questions about how heat affects our turf. Most of the time when there is heat stress on the turf there is also drought stress, and vice versa. So I usually lump those two situations together. But, first let me talk about heat stress.
As I’ve stated in other blog posts, the most favorable temperature for cool season grasses is 60 to 75 degrees F. But, many turfgrass species vary in their tolerance of heat. Perennial ryegrass, annual bluegrass and rough bluegrass will feel the effects of heat stress sooner (or at lower temperatures) than tall fescue.
I tell all my customers in the DC, MD & VA area to have tall fescue. Tall fescue has the best high temperature stress tolerance than any of the other cool season grasses. Depending on watering, it may go dormant in the middle of the summer. That’s fine. And it remains green all winter. I like that.
I mentioned this in an earlier post as well – species selection is key when starting out. Don’t plant warm season grasses in Wisconsin and don’t plant cool season grasses in Louisiana. Ever wonder why you can’t get St. Augustine grass seed easily in your favorite garden center in Maine? That’s because it won’t grow well there. You’d be wasting your money…and the seed. But, in the transition zone – sometimes those decisions are not that clear.
I will list below the cool season grasses in order of the most heat tolerant to the least heat tolerant:
Tall Fescue
Creeping Bentgrass
Kentucky Bluegrass
Red Fescue
Annual Ryegrass
Perennial Ryegrass
Annual Bluegrass
Rough Bluegrass
After species selection, two other important factors are soil moisture and air movement. Keeping the soil moist and the air moving over the turf helps the turf cool itself, enhancing its own, natural transpirational cooling ability. Ever see a nice golf course using fans on the surface? That’s what they are doing…helping the turf cool itself.
Think about the concept of “evapotranspiration” or ET. Not the movie about a little alien. ET is the sum of evaporation and plant transpiration from the Earth's land and ocean surface to the atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and bodies of water. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves. Evapotranspiration is an important part of the water cycle. An element (such as a lawn or tree) that contributes to evapotranspiration can be called an evapotranspirator. This is how plants cool themselves. Just like humans, if plants can’t cool themselves, bad things start to happen, usually resulting in death.
Now, above, I used the word “moist”. Don’t be confused. I mean moist for cooling purposes. See my blog post on “Irrigation”. Air flow has a distinct relationship with irrigation or watering. Moist does not mean submerged. Too much water, or having water pooled on your turf can result in disease. If your water runs off, or puddles on the surface, you are applying to much….too quickly.
Another consideration is the landscaping around the managed turf area. Are there things like plants, fences, or other “obstacles” that may block or minimize the movement of air over the turf area? Air flow is important to all plants.
I know this may conflict with other aesthetic or values based beliefs regarding landscaping. One such conflict is “turf or trees”. It is the never ending discussion between guys like me (a turfgrass warrior) and the arborists (tree huggers – literally). Turf guys will have turf growing right up to the base of a tree. The arborists will say that the turf is taking much needed nutrients from the trees. The tree guys will say you have to have a mulched bed all the way around the tree out to each tree’s drip line. Listen, if I had beds like that for every large tree on my property, I’d have no turf.
Maybe I was digressing, but, I believe trees, shrubs and turf can coexist in complete harmony. You just have to have a vision and you have to have an operations plan. Hey, I fertilize my turf and I fertilize my trees and shrubs. I cut my lawn and I prune my trees and shrubs. I take care of them all. Unfortunately, sometimes, you may have to make some tough decisions. Those decisions are also sometimes based on funding, personal preferences, prioritization and what is best for the plants. If you have to aggressively prune an area of trees and shrubs for your turfgrass – so be it. And, God forbid, if you have to surrender a portion of your turf area because of densely planted trees or shrubs – that’s your call too. Its a tradeoff. (Surrender is not a frequently used term in my vocabulary.)
I will be discussing cold tolerance next. And, another topic soon to follow is shade tolerance. This topic regarding the “conflict” between turf and trees also applies to dealing with shade.