I have an area under some trees that contain pachysandra. I want to encourage it to spread into a square shaped area about 20 feet by 10 feet or so. presently that area is spattered with grass etc. I am thinking of rototilling, the area etc to encourage the spreading. will that help?
What should I do. Also, by placing the black plastic edging on the outside, will that contain the pachysandra?

Thank you