In order to maintain a weed-free, healthy lawn, spring grass care is as much about prevention as fostering healthy growth. It may be surprising to learn that not all weeds are battled the same. Annual weeds are a different issue than perennia. A pre-emergent herbicide or a post-emergent herbicide may need to be used depending on the weed problems..
To start off it is important to know if the weed problem is annual. Crabgrass in a common annual. If a lawn has crabgrass, fertilization in spring should also include application of preemergent herbicides. These herbicides address weed control before seedlings emerge. This is accomplished by inhibiting seed germination.
A weed such as crabgrass begins causing issues in spring, when seeds germinate. The trouble arises in that most preemergent herbicides work against weed seeds and grass seeds, as well!
Overseeding is incompatible with application of most preemergent herbicides. Faced with competition from crabgrass though it may be difficult to establish new growth in landscaping.