Shady grass. Fertilize how often?

[M.Burns]

I've got a very shady yard in northern Ohio. What is the maximum I can fertilize through the growing season in April/May (with a medium or less spreader setting), and without concern of over fertilizing or burning the grass out come June or July? I've seen some who do a good job of keeping things green in yards with as much shade as mine. Thanks.

[nospambob]