The effects of shade on turf.
Shade has an instant and detrimental impact on grass as with less light grass is unable to grow properly. Long term effects on grass in shade are:
- At first it causes a shortening of grass roots. As energy is used by turf to make up for the lack of sunlight less is available for root growth and development;
- Then as shade continues it causes a reduction in turf shoot density and it begins to thin out;
- This lack of light results in the turf stretching out as it looks to find light (etoliation). This results in the grass becoming lighter in colour as this stretching means cell walls become thinner and weaker;
- Over time this results in grass having less ability to take any wear and unable to recover.
When turf is in shade it limits photosynthesis and carbohydrate production. Areas in shade also tend to suffer from limited air movement which increases the tendency for disease. Moss and algae issues also increase as areas in shade tend to stay damper.
How to manage grass in shade.
- The most obvious solution is to remove what’s causing it. If its a garden then cutting back trees can have a major positive impact on your lawn. However, if its a stadium then you ocviously haven’t got this luxury;
- The second option is make the right grass selection. If its a heavily shaded area choosing a grass that doesn’t handle shade well is not going to end well. Instead choose a shade tolerant variety to start with and it will save you heartache further down the track;
- Thirdly contrary to what many may think cutting back nitrogen is a good thing. The last thing that you want to do is promote lush, shallow rooted turf when it is already struggling;
- Raising the height of cut is a good thing in shade. It increases the leaf area available to capture what limited light is present and also will counter root shrinkage;
- Over watering turf in shade is a recipe for disaster. This will only encourage disease outbreaks and encourage the grass to root at the surface. Neither of those is desirable; a
- Use of plant growth regulators (PGR’s) like Amigo 120® helps counter turf leaf etiolation.
Dealing with shade by removing what’s causing it.
If you suspect that you have a shade issue the first step with dealing with it is identifying if this is the case and what is causing it. A useful tool for this is the Sun Seeker iphone app which identifies what’s causing the problem. You then have to decide what to do to fix it.
If the cause is a grandstand or the wall of a building it is not practical to remove it. However, if the shade is being caused by trees or shrubs you can thin these out or remove them. The Sun Seeker app allows you to identify what the cause is and at what time of day.
Pruning branches below 3-4 metres makes a massive difference and improves the amount of morning and afternoon sunlight. Thinning the tree canopy will also improve the “quality” of the light that reaches the turf surface.
Quality of light under shade.
The quality of light and how it impacts on turf in shade is discussed in more detail in the article “Using light“.
In the graphs below the x-axis represent the wavelengths of light from 300-900 nm, and the y-axis indicates the quantity of the wavelength of light. When you look at the wavelengths between 400 – 700 nm (between the red lines), you can see that the amount of far-red light (the area above red arrow) is similar to the amount of visible light under natural sunlight. For turf growth, poor light quality is generally defined as light that has a lower proportion of red to far-red light, and this is because grasses specifically “see” and respond to this ratio of red to far-red light.
A) spectral distribution of sunlight (red to far-red = 1.15), B) spectral distribution of sunlight in a greenhouse (red to far-red = 1.05), C) spectral distribution of sunlight passed through a selective plastic filter (red to far-red = 0.70), D) spectral distribution of sunlight under heavy tree shade (red to far-red = 0.40).
Select the appropriate grass type.
Grass in shade varies in its ability to grow. Bearing this in mind grass seed and turf selection plays an important role in any management strategy. As a general rule warm season turf needs more light than cool season turf with warm-season turfgrass varieties requiring two or more times the amount of light as cool-season varieties. Light requirements are further complicated by the fact that different cultivars of the same variety can vary in their light requirements. For example all couch cultivars don’t require the same amount of light.
Cool season turf under shade
Of all the cool season varieties creeping red fescue has the highest shade tolerance. However, in fact all the fine-leaf fescues including hard fescue and Chewings fescue are adapted to dry, shaded conditions. In moister soil options include rough bluegrass (Poa trivialis).
Warm season turf under shade.
Firstly, warm Season grasses like Kikuyu and Couch are NOT shade tolerant. A considerable amount of work has been done quantifying how much light turfgrass needs which is summarised below. Units such as out wi-fi sensor boxes fitted with PAR light sensors can monitor light levels 24 x 7 so pretty quickly you get a strong indication of where problems may exist.
Comparative shade tolerance of turf grasses | ||
Shade tolerance | Cool season | Warm season |
High | Fine fescue | |
Colonial bentgrass/poa trivialis | ||
Tall fescue | ||
Creeping bentgrass | ||
Kentucky bluegrass | Buffalograss | |
Perennial ryegrass | Zoysia | |
Kikuyu | ||
Centipedegrass | ||
Carpetgrass | ||
Bahiagrass | ||
Couchgrass | ||
Table showing the Daily Light Integral (DLI) mol-2 d-1 for Turfgrass. | |||
Warm season Turf | |||
Turfgrass Cultivar | Summer | Winter | Spring |
Tifway couch | 21 | 10.6 | 17.9 |
Tifgrand couch | 19.9 | 9.8 | 14.6 |
Celebration | 19.6 | 8.8 | 14.9 |
Seadwarf Seashore paspalum | 13.2 | 8 | 11.9 |
Diamond Zoysia (matrella) | 11.3 | 7.4 | 10.9 |
Palisades zoysia (japonica) | 11.2 | 8.2 | 11.2 |
Cool Season Turf | |||
Creeping bentgrass | |||
Tall fescue | >8.8 | ||
Perennial ryegrass | >20 | ||
Kentucky bluegrass | 11.1-24.1 depending on cultivar | ||
Reduce nitrogen fertilisation.
For grass in shade a general rule is to reduce the amount of nitrogen that is applied in full sun by by 50% as too much nitrogen results in soft succulent growth. Alternatively adopting a programme of “spoon feeding” nitrogen using a little and often approach is one to consider. This gives you considerable control and also flexibility so you avoid applying too much in one application.
Raise the height of cut.
Maintaining the height of cut as high as possible increases the leaf area available for light absorption and photosynthesis. However, dealing with turf in shade on sports grounds or golf greens, is often not practical. Be aware however that increasing the height of cut from 3mm to 3.5mm is a 16% increase in height so a little increase can have big benefits.
Bunnell and McCarty (2004) have shown that a 50% increase in the mowing height from 3.175mm to 4.7mm can cause a big increase the quality of TifEagle couch greens.
Dealing with turf in shade by reducing irrigation.
Light frequent irrigation helps manage the shortening roots caused by the shade.
Use PGR’s.
Use of Trinexapac-ethyl (Amigo 120) to deal with turf in shade counters some of the negative impacts of shade by increasing plant density and decreasing plant shoot etiolation.
- Stier and Rogers (2001) found that the use of PGRs like Trinexapac Ethyl (Primo), reduces shoot elongation and improves photosynthetic efficiency;
- Ervin et al found that although after 2 months turf quality of creeping bent grass fell below acceptable levels, repeat applications provide 33-44% better quality than untreated;
- We have found that regular tank mix applications of trinexapac-ethyl coupled with supplementary fructose applications will delay the decline of turf quality in shade.
© 2022, Gilba Solutions Pty Ltd, All rights reserved
After Graduating from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) before emigrating to Australia in 1993.
He followed this by gaining a Grad Dip in Business Managment from UTS and has worked in a number of managment roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.
He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.