|I found free ground cover,|
|Vinca is also called periwinkle. It is an evergreen vining plant that will cover an area, including one with dips and valleys, in a few short years. It is tolerant of acidic soils, wet or dry, and produces an abundance of flowers from spring through summer. There are white flowering vincas and purple flowering vincas. I have some growing beneath my hemlock and cedar trees and it looks fantastic. It won't climb the tree trunks the way that ivy will so I think it's a terrific plant if you want to cover a large area. It will take either sun or shade but I think the best leaf color is when it is planted in the shade.
If you're having trouble growing grass, the area probably isn't getting enough sunshine (grass won't grow well in the shade). I'd use a creeping, trailing plant such as vinca (that's why it's called a ground cover, because it covers the ground in a thick mat).
Hope this answers your question!