Maintaining Lawns In Shade
Lawn maintenance in shady environments is often difficult and frustrating. Light is required for turfgrass nutrient metabolism and physiological development. In shady conditions, the lack of sufficient and effective light is one of the most limiting factors in maintaining healthy, vigorous turfgrass. Lawn decline in shady environments is a common topic of discussion between homeowners and lawn-care professionals. This article covers what you need to know about maintaining a lawn in shady conditions.
Turfgrass Varieties and Shade Tolerance
One of the most confusing aspects of considering a turfgrass variety that may thrive in shady environments is choosing the best variety for the growing conditions. Time and time again my clients proclaim that the grass that they purchased was "made for shade" - unfortunately this cannot be further from the truth. No turfgrass is "made for shade"! After all, all turfgrass species and varieties available in Central Florida, with no exception, are grown in vast sod farms that are void of trees or shade structures - they are in fact exposed to full sun, all day long. Plants that prefer a shady environment thrive in shade and often experience sunburn when exposed to more sunlight than they are used to. In the nursery trade, plants that require shady environments are grown under shade cloth. Next time you visit a landscape nursery or one of the large box stores try to pay attention to the placement of plants in the retail area - some are in the full sun, some are under an overhang or shade structure, and some are inside the building - it all has to do with the preference of particular plants to sunlight exposure. Turfgrass is no different!
Now all that said, there are certainly turfgrass varieties that tolerate less sunlight than others - we refer to them as "shade tolerant varieties" in the industry. This tolerance varies between turfgrass varieties and between seasons. Some of these varieties have been around for quite a few years while others are relatively new to the industry.
Shade-tolerant St. Augustine Grass varieties that are currently available for purchase and installation in Central Florida include:
St. Augustine 'Bitter Blue' - One of the oldest St. Augustine Grass varieties. Bitter Blue is characterized as dark-green to blue in color and slightly denser than Floratam. This variety has good cold tolerance in comparison to other St. Augustine Grass varieties. Bitter Blue is susceptible to turf insect pests including Chinch Bugs, Sod Webworms and Armyworms. It is also susceptible to fungal diseases including Gray Leaf Spot, Large Patch, and root rot diseases. Nematodes can be problematic in Bitter Blue St. Augustine Grass. Bitter Blue should be mowed at 3.5-4 inches.
St. Augustine 'Citra Blue' - One of the newer St. Augustine Grass varieties in recent years. Citra Blue was developed by the University of Florida Turf Breeding program and became available in 2019. This variety is characterized by its dark blue color and dense canopy. Citra Blue performs well in areas that receive at least four hours of full, unfiltered light per day, or the equivalent of this amount of light under filtered-light environments. Citra Blue is marketed as more resistant to turfgrass diseases including Large Patch, Gray Leaf Spot Fungus, and Take All Root Rot - I think the jury is still out as to the validity of these statements. This variety is susceptible to injury by insects pest including Chinch Bugs, Sod Webworms, and Armyworms. Thatch can become problematic with this variety, especially if mowed too high. Citra Blue should be mowed at 2-3 inches. Mow higher within this range in shadier areas and during periods of cooler weather.
St. Augustine 'Palmetto' - This variety was discovered in the late 1980's by a sod grower in Florida and subsequently released as a registered variety in the early 1990's. Palmetto has a lighter green color than most other varieties. In my experience, Palmetto has been quite inconsistent in response to environmental stressors such as abnormally hot or cold temperatures, tolerance to intermittent lack of water, and tolerance to shady conditions. While Palmetto can often be seen growing well in partial shade, it does not tolerate dense shade, even if it is seasonal. Palmetto is very susceptible to Gray Leaf Spot Fungus as well as to Chinch Bugs, Sod Webworms, and Armyworms. It is also susceptible to nematode injury. In shadier sites under hot, humid conditions commonly found in Central Florida during the summer months, Palmetto tends to thin out and has a difficult time recovering. This variety should be mowed at 3-4 inches.
St. Augustine 'Pro Vista' - This is a relatively new, patented St. Augustine Grass variety from Scotts and is one of the most exciting varieties to hit the market in many years. While Pro Vista performs best when grown in at least 6-8 hours of sunlight, it tolerates less-than-ideal light conditions as well as other shade-tolerant varieties. Pro Vista is a genetically-modified variety, in which St. Augustine Grass 'Floratam' genes were modified to grow in a more prostrate orientation and conferred tolerance to glyphosate. This variety has a slightly darker green coloration as compared to 'Floratam' and grows a bit slower. Following installation, Pro Vista seems to take its time to establish, so patience is important. Cold response in this variety seems to be less favorable than in other St. Augustine Grass varieties. In my experience so far with Pro Vista, it appears to be as susceptible to insect pests and diseases as 'Floratam'. The jury is still out on the susceptibility of Pro Vista to nematodes and Sugarcane Mosaic Virus, the latter of which is a major untreatable problem in South Florida. Nevertheless, the ability to use glyphosate to manage otherwise uncontrollable weeds as compared to other St. Augusine Grass varieties boasts a major advantage in my book. Pro Vista should be mowed at 3-4 inches.
St. Augustine 'Seville' - This variety has been the "go to" for shadier locations for many years. Under ideal growing conditions and proper maintenance, Seville forms a dense, carpet-like lawn that is arguably more attractive than any other St. Augustine Grass variety. This is the only true "dwarf" type St. Augustine Grass that is currently available in Central Florida. Over the years, Seville seems to have become more susceptible to injury by many fungal diseases and nematodes. One of the well-known characteristics of Seville is its tendency to form thick thatch over time, especially if mowed too high (which it commonly does). When grown in shadier sites, Seville tends to decline rapidly during the summer months when improperly maintained and/or if rainfall and cloud cover is frequent. This variety is not cold-tolerant. Seville is very susceptible to turfgrass diseases including Large Patch Fungus, Gray Leaf Spot Fungus, and Take All Root Rot Fungus, as well as to insects pests including Chinch Bugs, Sod Webworms, and Armyworms. Seville is probably the most susceptible to nematode injury of all of the available St. Augustine Grass varieties. Over the years, many sod farms have opted to stop growing Seville in favor of other varieties. I believe that this variety will fall out of popularity in the years to come. Seville should be mowed at 2 - 2.5 inches.
We frequently meet with current or potential clients regarding their declining lawn in areas that are exposed to less-than-optimal sunlight.
Discussion of turfgrass light requirements and exposure in terms of hours of sunlight received can be very arbitrary because visual light availability cannot be measured. The light required for photosynthesis must be within a certain wavelength. If filtered through tree canopies, the total amount of photosynthetic light that actually reaches the lawn is highly-influenced by many factors including:
- Season of the year (daylength)
- Angle of light penetrating canopies
- Tree canopy density
- Cloud cover
- Temperature