Perennials may be planted almost anytime during the growing season, but spring planting is preferred. Remove the containers before setting plants in prepared planting holes. If plants are in peat pots, remove the top edge of the peat pot to prevent it from acting as a wick, drying out the pot after planting and injuring the roots. Give the plants space to grow over the next few years. This often is 1 to 3 feet apart, depending on the size of the young plant.
Perennials usually show up best when planted in clumps or groups of plants of the same variety.
This is especially important for a few weeks after planting. A light sprinkling of fertilizer around the plants 4 weeks after planting will aid growth. In addition to adding organic matter to the soil, mulch in the summer helps conserve moisture, moderate soil temperatures, prevent clay soils from baking and cracking, and reduce weeds. During the winter a mulch helps to protect newly planted perennials and keep soil temperatures warm, and to stimulate new growth which is easily killed by cold. Stake tall plants, such a delphiniums, or top-heavy ones, such as peonies, when they are set out.