Here is the problem. Yes, landscape liner prevents weeds from growing. But it prevents everything else from growing! It also prevent ground cover to creep along the dirt and grow as well. I pulled the landscape liner out of the sections I was going to work on, and I did it too soon before planting. When I tried working with the hard-packed soil underneath the liner, it was impossible. It was damp, full of clay, had few earthworms and just sat in clumps. After I put my plants in, I had one problem after another. Poor drainage caused root rot. I had mold and mildew. I also had slugs. In hindsight, I should have pulled the liner off in the fall. Turned the soil over. Then mixed in peat, mulch, grass clippings as well as mulched dead leaves all throughout the beds, and let them sit and breath through the winter. Come spring I would have had a much happier shade garden.
So I performed plant triage to my shade garden. I bought a lot of peat and black forest soil conditioner, and I aerated around all my plants with a small hand tiller. Than I mixed in the materials and tilled again. The death and destruction seems to have stopped. I am hoping for a better year next year!
If you are going to use landscape liner, DON'T. Just weed the old fashioned way! I will give you an update next year.