Plants and Sunlight – How Sunlight Affects Grass Growth


Sunlight: Day Length

The alternating pattern of day and night greatly affects grass growth and development. The length of time between when the sun rises and when it sets is called day length.

The relationship between plants and sunlight is very complex. Changes in the day length function as the timer or trigger that starts or stops certain turf growth processes. Day length changes initiate growth and flowering and also let the plant know when to start to prepare for winter dormancy.

Turfgrass Flowering

As a general rule, cool season grasses are long-day plants and warm season grasses are short-day plants. This means that as day lengths increase in spring, cool season grasses begin to flower. Conversely, shortening day lengths in the mid-summer trigger flower development in warm season grasses.

Northern Hemisphere Day Length:

  • December 21st = shortest day of the year
  • June 21st = longest day of the year

Sunlight and Grass Growth

Temperature, much like day length, is also a trigger to grass growth. Longer and warmer days result in more sunlight that can be used for photosynthesis. Shortening days and cooler temperatures favor root development and decreased shoot growth, which help prepare the plants for winter.

Sunlight Intensity

Full sunlight is the ideal growth conditions for most turfgrass plants. The amount and also quality of sunlight reaching the plants influences grass growth and development.

Factors influencing sunlight intensity:

  • Time of year / Day length – Days lengthen after December 21 and begin to shorten after June 21.
  • Latitude – The closer you are to the equator means that day lengths change less and stay closer to 12 hours/day and 12 hours/night.
  • Time of day – Sun angle is low during the morning and afternoon.
  • Atmospheric Filtering – Cloud cover, pollution or shade from trees, other plants and buildings reduces the amount of sun reaching the turf.
  • Topography – South-facing slopes get more sunlight than north-facing slopes resulting in higher soil temps. The altitude where the lawn is grown also influences how much light reaches the turf. Turfgrass grown in the mountains receives higher intensity light because it is closer to the sun.

How much shade is too much shade?

Turfgrass needs a minimum amount of light to grow. Portions of a lawn may be shaded while others may be in full sunlight. Grass that receives too much shade will slowly decline over time. A lawn, or area of a lawn, that does not get enough light will have long, spindly leaf blades and stems because it’s trying to grow toward sunlight. This depletes carbohydrate reserves and reduces the lawn’s overall health and vigor.

Lawn Care to Optimize Sunlight and Maximize Grass Growth –

Because the relationship between plants and sunlight is so complex, there are a number of different factors homeowners must consider when deciding which turfgrass plants to establish in their lawn. The professionals at Scotts LawnService are highly trained to help you find the best turfgrass species to tolerate the unique conditions in your lawn.

Scotts LawnService is the trusted industry leader for professional quality lawn care. Our exclusive lawn care products include premium grass seed and professional-grade fertilizers; our lawn service teams are comprised of highly trained, industry-certified professionals. Contact a representative today to learn more about the role of sunlight, help choose the right turfgrass type for your lawn, producing a lush, thicker lawn that only Scotts LawnService can deliver.