The effects of shade on turf.
- Shortened roots
- Reduced shoot density
- Etoliated growth of stems and leaves.
- Decreased plant health
- Increased disease susceptibility and
- Reduced wear tolerance and recovery
When turf is subjected to shade it limits photosynthesis and carbohydrate production. Shaded areas also tend to suffer from limited air movement which increases the tendency for disease. Moss issues are also likely to increase as areas in shade tend to stay damper.
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 and more susceptible to wear etc.
How to manage turf in shade.
- Remove what’s causing it
- Select the appropriate grass type
- Reduce nitrogen fertilisation
- Raise the height of cut
- Reduce irrigation and
- Use PGR’s
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. We have had great results by using the Sun Seeker app which not only identifies what’s causing the issue but gives a good indication of how to deal with it.
Obviously if the cause is a grandstand or the wall of a building this is not feasible. However, if shade is being caused by trees or shrubs you can potentially 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 can make a massive difference and improve 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 is discussed in more detail in “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 looking at wavelengths between 400 – 700 nm (between the red lines), we can also see that the amount of far-red light (area above red arrow) is similar to the amounts of visible light under natural sunlight, or even in slightly less quantity. For plant growth, poor light quality is generally defined by light that has a lower proportion of red light to far-red light, and this is because plants specifically “see” and respond to the 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.
Grasses have varying abilities to grow in shade. As a general rule warm season turf needs more light than cool season turf as warm-season turfgrass varieties require two or more times the amount of light as cool-season varieties. Light requirements are further complicated by the fact that different cultivars can vary in their light requirements. For example all couch cultivars don’t require the same amount of light.
Cool season turf
Creeping red fescue has the highest shade tolerance but all the fine-leaf fescues including hard fescue and Chewings fescue are adapted to dry, shaded conditions. If the soil is moister other options include rough bluegrass (Poa trivialis).
Warm season turf.
Firstly, warm Season grasses like Kikuyu and Couch are NOT shade tolerant. A considerable amount of work has been done quantifying turfgrass light requirements which is summarised below.
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.
A general rule is to reduce the full sun Fertilizer rate by 50% for areas in shade. Too much nitrogen results in soft succulent growth
Raise the height of cut.
Maintaining the height of cut as high as possible will increase the leaf area available for photosynthesis. However, dealing with turf in shade in this manner, is often not practical. Do realise however that increasing the height of cut from 3mm to 3.5mm is a 16% increase in height!
Bunnell and McCarty (2004) have shown that a 50-percent increase of mowing height (from 1/8 inch to 3/16 inch) can increase the quality of TifEagle Bermudagrass greens significantly.
Dealing with turf in shade by reducing irrigation.
As roots become a shortened a light and frequent irrigation regime should be adopted.
Use PGR’s.
Dealing with turf in shade by using Trinexapac-ethyl (Amigo 120) will counteract some of the negative effects 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), have shown to limit shoot elongation and improve photosynthetic efficiency.
- Ervin et al found that although after 2 months turf quality of creeping bent grass fell below acceptable levels repeated applications provided 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 inevitable deterioration of turf quality in shade.
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