Dandelions can pop up by the dozens in almost any lawn. The bright yellow flowers are generally small, but the stems grow much faster than grass, which make them extremely visible, even from a distance. Worst of all, dandelions keep growing back no matter how many times you cut them with a lawn mower. An effective solution to killing dandelions is an application of a selective herbicide. These herbicides kill any weeds they touch, but will not harm grass.
Apply a selective herbicide, preferably a 2,4-D or MCPP, to the entire lawn according to the directions of your particular product.
Let the herbicide sit and soak into the soil for at 24 hours before you water the lawn. If watered too soon, you could dilute the herbicide and render it ineffective.
Water the lawn heavily with sprinklers for one hour after the 24-hour period. Repeat this once per week. Dandelions thrive in lawns that are watered lightly multiple times per week, so infrequent, heavy watering sessions will reduce the chance of the dandelions coming back.