I have a large portion of my backyard planted with Vinca (among shrubs and trees) It has been like that when I bought the house 2 years ago. The groundcover is not very dense though.

Any idea on what I can do to make it more dense and vigurous? The soil has plenty of clay and it is normally rather dry. The area is mostly shaded, but conditions vary. I have been spot watering for the last couple of years when caring for some larger plants in these beds, I didn't water neccessary the whole area with groundcover. It seemed to make little difference to those spots. I also appied Dryroots everywhere last spring, and again I haven't seen dramatic improvements.

Does it need to be trimmed? If yes, when and how? Anything else I could do?

Thank you.