Should I fertilize the lawn in summer?

FAQ
Question: 

Should I fertilize the lawn in summer?

Answer: 

Do not fertilize Kentucky bluegrass and other cool-season grasses during the summer months (June, July, and August).  The best times to fertilize cool-season grasses in Iowa are spring, mid-September, and late October/early November.  When fertilizing the lawn, do not apply more than 1 pound of actual nitrogen per 1,000 square feet in one application.