Fir year customers find that weeds are reduced in their lawn, both crabgrass and broadleaf weeds.  This may result in a number of bare spots where the weeds once grew.  The best solution for these bare spots is an over-seeding in late summer and fall seasons.  Many Lawn Science customers have found the existing grass will fill in these bare spots over a period of time.  If the bare areas are large or abundant, over-seeding is the quickest way to thicken the lawn.