When the grass is sparse or has issues with weeds, however, it may be necessary to feed and weed more regularly to promote better growth
Feed: If your goal is to encourage growth while reducing weeds in your yard, then you should use a slow release fertilizer such as ammonium sulfate or ammonium nitrate. These fertilizers release nutrients over time to help promote root development for strong stems.
Feed is most often used in late fall and early spring. Weed is most often used when rain is forecasted after an extended period of time without rainfall.
If you are looking for thick, lush green lawns that make your garden look like a lush green forest, then feed your lawn when the weather is warm and weed your lawn when it's cool outside. If you are looking for thin, stringy lawns that don't get much sunlight but still look healthy, then feed and weed your lawn every other week.