Answer: Generally speaking, most perennial beds are prepared by first removing the existing vegetation and then loosening the soil and working in an ample supply of organic matter. In this case, in order not to disturb the moss, you could prepare generously sized individual planting holes for your perennials.
Some sturdy perennials to consider for a slope in sun to part sun would be creeping phlox, coreopsis, daylilies, dwarf bearded iris, salvia, purple cone flower, black-eyed Susan, catmint, plumbago, perennial geraniums and assorted sedums. You could also add some spring-flowering bulbs such as crocus. After planting, be sure to apply a layer of mulch and water regularly the first summer to help the plants establish themselves.
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