Answer: There are many groundcovers suitable to moist areas and shade, and as a bonus, that are perennial in your zone. One is Aegopodium (Snow on the Mountain), it spreads very quickly and can be invasive. It is however, an excellent ground cover for shady, moist areas. Another good choice is Tovara virginiana 'Painter's Palette'. Lysimachia nummularia 'Aurea' is another personal favorite of mine. At planting time, perhaps you could incorporate some organic matter such as compost, leaf mould, or composted cow manure into the area. This will not only get the new plants off to a good start (and the current plantings too), but it will also improve the soil's composition and help the heavy clay have better drainage. Let us know if youneed a source for anything.
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