The answer to this question has more to do with how you want your lawn to look, than what it needs. Current recommendations from Michigan State University's Extension Service indicate that 4 to 5 pounds of nitrogen should be applied per area over the course of the summer. This amount should never be applied all at one time. Decide how many applications you are willing to make and divide up the nutrients needed. You can see that somewhere between 4 and 6 applications are needed to be sure your lawn gets the nutrients it needs to be healthy.
Of course there is a price to pay for fertilizing your lawn - - it grows! That means its going to need water and then it'll have to be cut. Be sure to see our recommendations for these two critical lawn care practices. Just remember, the more you fertilize, the more the lawn will grow.