Some seepage is considered ideal, but a filled in pond liner works ok. I have a bog in a sunken pond liner and grow a number of plants in it such as Marsh Fern (Thelypteris palustris), Iris versicolor, Filipendula rubra, Mimulus ringens and several others. At a previous location I had a bog with pitcher plants, sundews, and Venus fly traps, really a lot of fun. There are a lot of plants that would relish Robin's site. My current bog has a few small holes drilled about 2 inches from the top at the slightly downhill end for excessive water to drain slowly past Swamp Milkweed, Joe Pye Weed, Marsh Mallow, Baptisia australis and Ostrich Fern. Best to fill with soil almost to the top of the liner so that water does not stand long and encourage mosquitoes.
