When is the best time to sow grass seed?

FAQ
Question: 

When is the best time to sow grass seed?

Answer: 

Late summer (mid-August to mid-September) is the best time to establish a lawn from seed in Iowa.  Late summer seeding has several advantages over spring seeding.  The seeds of cool-season grasses germinate quickly in the warm soil of late summer.  Once the seeds germinate, the warm days and cool nights of early fall promote rapid turfgrass growth.  The growing grass also has less competition from weeds as few weed seeds germinate in fall.