Lawns are usually comprised of one or two different types of grass. Any plant that grows in lawn grass will look out of place and will need to be removed for aesthetic reasons. Removing weeds from a lawn requires equal measure good cultivation practices and lawn care as well as application of herbicides to destroy the weeds. Proper lawn care, however, is usually enough to prevent weeds from growing and kill those that are already present.
Regularly mow your grass down by 1/3 of the grass blade at a time. This encourages thick grass growth, which chokes off sunlight and resources for weeds in the lawn. Mowing regularly also cuts weeds before they are able to release seed and propagate.
Apply a pre-emergent herbicide to the lawn two to three weeks before the weeds begin to seed. For most weeds, this is between May 5th and May 20th. Pre-emergent herbicides kill the seeds before they are able to germinate.
Apply a post-emergent herbicide to the lawn to kill weeds once they are grown. Liquid sprays work better than powder, as post-emergents require absorption through the leaves of the plant. Apply post-emergents in the early fall between August and October or in the spring between May and June.