The answer to 'why is my grass yellowing' is that there are several common causes, including nutrient deficiencies, drought stress, disease, or pest infestations. Yellowing grass can be a sign of an underlying issue that requires attention.
Nutrient deficiencies, especially a lack of nitrogen, are a common cause of yellowing grass. This can happen if you haven't fertilized regularly or if the soil is depleted of essential nutrients. Drought stress from lack of water can also cause grass to yellow and turn brown. Fungal diseases and insect pests are other potential culprits that can lead to discolored, unhealthy grass.