Thank you for your question.  It sounds like you have some very happy hydrangeas.  I would suggest thinning the hydrangeas by digging them out over the course of a few years.  You may even consider offering the hydrangeas to others and end up with plenty of help to dig them out.  If you choose to remove the plants via an herbicide, keep in mind that you will need to ensure you only apply to plants that you want to kill.  Also, you may need to wait before planting new plants in the area.  

If you choose to proceed by thinning the hydrangeas, you can plant wildflowers in empty spaces.  Several of our native wildflowers are vigorous and well-suited to filling in quickly.  A list of native plants suited to our climate can be found here: https://extension.umn.edu/find-plants/native-plants  

If you have a challenging site, check out the University of Minnesota Extension Service publication, "The Best Plants For 30 Tough Sites," located here: https://conservancy.umn.edu/handle/11299/51549  

Can you suggest a web site or face-book address to contact people wishing to uproot plants in my area (Macalester Groveland)

Hi,

I would suggest searching Facebook for gardening groups in your area.