There are a few times when it is a good idea to spray your dandelions. One reason to spray them is during the early stages of their growth before they have produced many flowers. This is because when the flowers are pollinated, they will create seed heads. If you do not kill the weed before they produce seeds, then the weeds will come back in future years and take over your garden or lawn. You can also spray them if you see them growing in an undesirable location, such as next to a sidewalk or driveway. If you have a problem with dandelions invading your garden or lawn, one way to control them is by using herbicides specifically designed for this purpose.