When should I fertilize my lawn?

FAQ
Question: 

When should I fertilize my lawn?

Answer: 

Most lawns in Iowa are comprised of Kentucky bluegrass and other cool-season grasses.  Cool-season grasses grow best in spring and late summer/early fall when environmental conditions are usually favorable.  Applications of fertilizer should coincide with favorable growing conditions.  In Iowa, cool-season lawns can be fertilized in spring (April or May), mid-September, and late October/early November. 

Do not fertilize Kentucky bluegrass and other cool-season grasses during the summer months (June, July, and August).