Fertilizer is an important lawn care practice, as it influences grass color, ability to recover from stress and helps prevent weed invasions and diseases. There are a variety of fertilizer applications. With the exception of “Weed and Feed”, it is best to apply them just before a rainfall, as they need to be watered in. Fertilizers with weed killers need to sit on the lawn for a day or two, to allow the weed killer to do its task, and then it should be watered. Never apply “Weed and Feed” just before rain is expected, as you are only harming the environment. How often you apply fertilizer also depends upon the area and climate you live in. The most common is the three or four applications. For lawns, fertilizers containing controlled-release nitrogen sources are suggested for most applications, because they help assure uniform growth and do not readily burn grass.