How Much Sunlight Does Turf Grass Need?

• Time of year. The Earth is closest to the sun in early January and farthest from it in early July, altering the Earth’s heat and light.
   
• Time of day. The sun’s angle is lower during the morning and afternoon as light intensity gradually grows from sunrise and then wanes toward sunset.
   
• Length of day. Days get longer after December 21 and begin to shorten after June 21, altering how many hours of sunlight your grass gets. Changes in day length function as a timer or trigger that starts or stops turf grass growth. These changes initiate growth and flowering and start the process of hardening off for winter dormancy.

• Latitude. Locations around the equator receive maximum light intensity as day length changes less and stays closer to 12-hour days and 12-hour nights. This intensity wanes as you move away from the equator.
   
• Atmospheric filtering. Cloud cover, pollution, pollen particles or shade from plants and buildings reduce the amount of sun reaching your yard.
   
• Topography. South-facing slopes get more sunlight than north-facing slopes, resulting in higher soil temps. Your lawn’s altitude also influences how much light reaches the grass—turf grass grown in the mountains receives higher intensity light because it is closer to the sun.

In the northern hemisphere, the longest day of the year is June 21 and the shortest day is December 21. Day lengths increase in spring, which is why cool-season grasses are considered long-day plants—they begin to flower in the spring as days get longer. Warm-season grasses are considered short-day plants because they are triggered to develop in mid-summer as the days start to get shorter.

Working in tandem with day length, temperature also affects turf grass growth. Longer days are typically warmer, resulting in more sunlight to be used for photosynthesis. Shortening days bring about cooler temperatures that favor root growth, decreased shoot growth and winter preparations.

Different types of turf grass need different amounts of sunlight for optimal growth, but all need require a minimum amount of light to grow. Most turf grass management guidelines agree that lawns should receive at least six hours of sunlight each day, tolerating about 20% filter from trees.

Your lawn’s sunlight-to-shade ratio is unique based on your home’s environmental and landscaping factors. Some front yards are heavily shaded even though their backyards are in full sunlight. As long as your grass species is adapted to shade and it receives enough sunlight, growing a healthy lawn in shade shouldn’t present a problem.

But for lawns that don’t get enough sunlight, the results can be depressing: long, thin leaf blades with spindly stems bending toward the sunlight and depleting their carb reserves until the lawn’s strength gives out and its health eventually declines.

As you grow into your home, your yard grows with you. In some cases, shade conditions can change over the years as trees grow larger and create more shade. This increase in shade is often so gradual that it goes unnoticed. But eventually, your turf grass will start to lose its luster as it receives less and less sun.

A quick solve for this are shade-loving ground covers and perennial plants that have a high tolerance for heavy shade conditions. If you live in a climate that can support both warm- and cool-season grasses, renovation is possible in certain areas as cool-season grasses are much more tolerant of the shade than warm-season turf grasses. Although both warm- and cool-season grasses do best with eight or more hours of sun, cool-season grasses that are shade-tolerant typically need only 50% full sun.