Poorly drained soils can often be improved by working in large amounts of compost or peat. When planting peonies, dig a hole large enough for the entire root system. Place the peony plant in the hole so the buds are 1 to 2 inches below the soil surface. Fill the hole with soil, firming the soil around the plant as you backfill. Then water thoroughly.
Straw is an excellent mulch.
Mulching will prevent repeated freezing and thawing of the soil during the winter months that could damage the plants. Remove the mulch in early spring before growth begins. Transplanted peonies will not bloom well the first spring. In fact, it's advisable to remove any flower buds that form the first year to maximize plant growth. Transplanted peonies should bloom well by the third or fourth year.