Oakleaf hydrangea fall leaf color can be absolutely fantastic. Plants will color more heavily in sun than in shade, but if a few rays hit the leaves, shades from brick red to wine will appear. These are truly four season plants and if you are gardening where they will grow and don't have one in your shade garden, put it right up there at the top of your list. These hydrangeas perform best, so I have read, where they get some direct sun. Sometimes a tinge of yellow or purple occurs in fall, but nothing spectacular.
Flowers are white, changing to purplish pink and begin in mid summer.
Yellowish-white fertile flowers predominate, with sparse, showy sterile flowers. This is a very common form, the 'Pee Gee' hydrangea, hailing from Japan and introduced in 1862. To get massive flower trusses that will weigh down the branches, Dirr says you need to thin the plant to five or ten primary shoots and fertilize and water it well. Tardiva' flowers have a better balance of fertile and sterile florets on large panicles that age from cream to pink. This cultivar, distributed to the trade by the JC Raulston Arboretum in North Carolina, received the RHS AGM in 1990.