Black walnut tree and sedge compatibility
I am going to gradually replace much of the "lawn" in my backyard with sedges of various kinds, and I want to begin with the difficult area under two large shade trees, a black walnut and a cottonwood (they are side-by-side in a sort of tree island at the side of my yard). Do sedges/caryxes generally grow under black walnuts? Also, my garden center suggested pachysandra for that site but I think it is considered invasive, yes?
Sedges (Carex sp.) are tolerant of juglone, so they should be fine to plant in the area under your black walnut tree. http://www.johnson.k-state.edu/docs/lawn-and-garden/in-house-publications/trees-shrubs/Landscaping%2...
Japanese pachysandra (Pachysandra terminalis) is invasive in Maryland. Allegheny spurge (Pachysandra procumbens) is a native plant that could be used instead of the Japanese variety. https://extension.umd.edu/hgic/groundcover-list