Can hydrangeas grow under an oak tree?

Not likely .Hydrangeas prefer part sun.

There's a hydrangea called "Blue Billow" that will take a lot of shade.

Read the tag on the plants, some take shade.

You certainly can! Digging with tree roots is somewhat hard but worth the effort! I have a 75 year old mulberry tree that shades our hot tub and have hydrangeas and hostas surrounding the tree. " Little Lime" should do well and any " Endkes Summer".

I have many, many hydrangeas in my yard and they are easy to grow. Love water thus " hydra". I certainly would start with perhaps a two gallon size so digging the hole would not be overwhelming if you dig into too many roots. Suggestion . . . . "LImelight" and " Oakleaf" hydrangeas do well in sun so you might consider planting these elsewhere. Both have panicle shape blooms and are gorgeous! HAPPY GARDENINH!

Yes I have hydrangias planted under a tree and they do very well