Hello, I am new to this forum and am interested in some feedback.

I have two small gardens in the corners of the back of my yard, and about 26' between the two gardens of empty space. I'd like to plant either ornamental grasses or hydrangeas along the back fence and am wondering how many to plant and advice about spacing. The fence is 6' tall so I'd like tall grasses. I don't want to fill the whole space, (horizontally speaking) and am thinking a few feet on either side of the grasses, between the grasses and the gardens, would look best. Though am open to ideas! I also love hydrangeas and think they'd do well here too, though this spot does get a lot of late morning and afternoon sun. Lastly, my property slants downward from the house towards the back fence, so if we have a lot of rain, this area can (rarely) be under water or quite wet. I'd need grasses/hydrangeas that can tolerate a lot of water on the rare occasion.

Thanks in advance for your ideas!