A peace lily that is watered regularly can display numerous blooms and vigorous leaf growth. The roots share in this vitality and may crowd the container. Root structure can become plentiful enough to deter proper moisture retention in just a couple of growing seasons. The blooms decrease in number and quality, and the whole plant may begin to droop from lack of water. A distressed specimen should be watered frequently before replanting, until its normal posture returns.
Early spring is the best time to replant peace lilies, before the summer blooming begins. A plant that is in dire need may be replanted at any time of year. Scheduled annual replantings might prevent any midseason propagation that could disrupt bloom rates. Division of the rootstock is fundamental for plant propagation and should be done whenever the roots emerge from the top of the soil or the bottom drains of the container.
Prepare new containers for each portion of the plant to be harvested. Drainage material placed in the bottom of the new pots prevents root rot and keeps the soil from compacting. Gently separate a quantity of stems and their roots away from the remainder of the plant. Comb the tangles apart with your fingers to tenderly free adjoining roots. Some damage to the roots is inevitable, but no profound effects are likely.
Provide a warm and shady environment for the transplants until normal growth is established. Keep the new containers in an area free from drafts that maintains a temperature of about 70 degrees Fahrenheit. Mist the leaves daily, and water the soil two to three times a week. Position the robust new plants in partial shade as summer approaches, and maintain this light level through the blooming season. Peace lilies require more light and less water in winter, when growth slows.