Not all shade is equal. Some types of shade are much worse than others for turf health and growing conditions. When turf struggles in the shade it is often attributed to a lack of light, but we rarely discuss the type of light. Trees don’t just block light, they filter it. The total amount of light (quantitative shade) matters, but qualitative shade (the quality of the light wavelengths) is equally important.
Light wavelengths are measured in nanometers (nm) and affect turf plants in different ways. Below is a general breakdown of the turf-specific wavelengths.
Blue Light (400-500 nm)
- Critical for photosynthesis
- Promotes strong leaf growth and structure
- Often reduced in shady conditions, contributing to weaker turf
Green Light (500-600 nm)
- Not as efficient as blue or red light for photosynthesis
- Mostly reflected, not absorbed by the plant
- Still plays a role by penetrating deeper into the turf canopy than other wavelengths
Red Light (600-700 nm)
- Highly efficient for photosynthesis
- Works together with blue light to regulate plant development
- Reduced red light can impact turf growth and density
Far-Red Light (700-740 nm)
- Not used in photosynthesis but affects plant behavior
- Alters growth patterns like stretching and leaf size
- When increased relative to red light it can signal plants to grow taller and thinner as a stress response
- Can turn off certain growth indicators within the turf plant
In essence, trees filter out a lot of the “good” blue and red light and let the less useful far-red light through when the blue and red light wavelengths are absorbed by the tree leaves for photosynthesis. This means that the turf is not receiving the quantity of light it needs for photosynthesis, and the diminished amount of light that is coming through has negative effects. This is like dying of thirst in the desert and the only water available is poisoned.
The next time growing environments and available sunlight are discussed at your golf course, remember that the quality matters as much as the quantity. Tree management and pruning increase the available light, and increase the amount of light in the blue and red wavelengths that reaches the turf below.
West Region Agronomists:
Brian Whitlark, regional director, West Region – bwhitlark@usga.org
Ross Niewola, agronomist – rniewola@usga.org