Chemicals for the lawn, when applied properly, can help reduce insect pests and weeds and can increase the growth and overall health of the grass. They are very potent, however, and should always be used carefully; failure to follow instructions and use the proper amount can result in leaf burning and unhealthy (shallow) lawn root systems. Because of the potency of lawn chemicals, it's very important to keep children and pets away and to clean up any spills immediately.
The most common type of lawn chemical is a lawn fertilizer, which can be applied in granular or liquid form and can contain several essential elements in combination or a single needed nutrient. A complete fertilizer will contain the chemicals needed to provide nitrogen (N), phosphorus (P) and potassium (K); the percentage of each will be indicated by the row of numbers across the front of the bag: 3-1-2 or 4-1-2 are common ratios that are recommended by the University of Illinois Extension.
Getting rid of harmful bugs is another common problem for the homeowner, and pesticides applied to the lawn can do the job well. These chemicals are strong and should be applied with care. There are different kinds of pesticides meant to effect different kind of insect pests; however, most chemical pesticides will kill some beneficial bugs as well as harmful pests, so it's best to use these as a last resort. Pesticides should never be stored, so buy only as much as you need for an application and dispose properly of the remainder.
It's may be the homeowner's greatest frustration--the fact that weeds often grow better than the desired grass. The chemical solution is a granular or liquid herbicide, formulated to kill weeds without harming grass. It can still cause foliar burn, however, so it should be applied with caution. Many herbicides come in small containers and can be applied to individual weeds or patches. For more extreme cases, an herbicide can be applied with a spreader or sprayer. Caution should always be used because herbicides can be dangerous for pets and humans.