According to HydrangeasHydrangeas.com, hydrangeas prefer morning sun and afternoon shade, especially the commonly grown macrophyllas. The further north a hydrangea is planted, the more sun it needs. Hydrangeas in very cool climates in the northeast or northwest United States may do well in full sun all day.
While different varieties of hydrangea vary in their need for sun, no hydrangeas do well in heavy shade. Panicle hydrangeas, such as the PeeGee or paniculata hydrangeas, tolerate more sun than other varieties and need at least five hours of sun each day. Oakleaf hydrangeas also produce healthier and more colorful flowers if they receive full sun. Frequent watering helps hydrangeas tolerate more sun.