It’s shaping up to be a cruel summer for Manhattan’s apartment landlords.

Last month, the median rent fell 1.3 percent from a year earlier to $3,307, according to a report Thursday by appraiser Miller Samuel Inc. and brokerage Douglas Elliman Real Estate. It was the second straight July with a decline and came after a 2.8 percent year-over-year drop in June.

Rents are slipping in what’s traditionally the peak season for apartment demand. Landlords tend to rely on the months of May through August -- when the city is swarming with new college graduates -- to fill their units at higher prices before temperatures, and tenants’ appetites for moving, cool.

Landlords contending with an oversupply of apartments had to offer sweeteners, such as a month’s free rent or payment of broker fees, on 35 percent of new leases in July, up from 27 percent from a year earlier, the firms said.

And renters weren’t exactly jumping at the chance to move. A total of 6,145 new agreements were signed in July, just 0.2 percent more than a year earlier.