If you have compacted, poorly drained soil, dig in 1 to 2 inches of compost to improve the soil's fertility and ability to regulate moisture. Covering bare soil with 2 to 3 inches of bark chips may also control moss, though Dr. Hudson cautions that slime molds (which look totally gross but cause no harm) often grow on cool, damp mulch. During dry periods in the spring and summer months, water your flowerbeds for 30 minutes once or twice a week instead of for a few minutes each day. This allows the soil to dry between waterings and also encourages your plants to develop more extensive root systems.
But perhaps the best solution is to beat nature at her own game and, after amending the bare spots with compost, fill them in with groundcovers that complement your flowerbed design. Low-growing plants that perform well in shade include lungwort (Pulmonaria spp.), ginger (Asarum spp.), Hakone grass (Hakonechloa macra), and Liriope spp. If all else fails, try to enjoy the moss for what it is—a self-planting, maintenance-free, green groundcover.