The amount of sunlight your grass gets may vary throughout your landscape and cause natural thinning over time as well as slow green up. The shade factor may be caused by trees, large shrubs, fencing and or buildings. The amount of sunlight your landscape gets may also vary due to the position of the sun as it passes over during the day. Landscapes that get early morning and afternoon sun may green up sooner than lawns that get late afternoon sun. The amount of sunlight is critical for the photosynthesis process to supply the root system with enough energy to support the top growth. When a certain threshold is crossed and the amount of sunlight provided to the plant is not enough sunlight, the root system will begin to die out and the grass begins to thin. In other words the grass starves to death.               

Most warm season turfs in this area require 8-10 hours of good direct sunlight (not filtered) to grow the way Mother Nature intends them too such as bermuda grass. Some zoysia type turfs do well in areas that receive 6-8 hours of direct sunlight. Cool season grass like turf type fescue can do well in 4-6 hours of direct sunlight in most cases.

If an area of your lawn is thinning due to the shade factor your options are to remove the object causing the shade (trees or shrubs). If the object cannot be removed then you can try a more shade tolerant turf like emerald zoysia or fescue. If these are not an option than you may try ground cover along with mulch and plants or all of the above.