Peace lilies (Spathiphyllum spp.) -- those heaps of glossy green leaves so often given as gifts of remembrance and hidden from small animals due to their toxic sap -- are valued for their white bloom covers, called spathes. Early cultivars bloomed annually in late winter or early summer, like their tropical ancestors. Newer hybrids rebloom or bloom intermittently from late winter through spring. All peace lilies' flowering success is determined by their environment.
About Those Blooms
Peace lilies are in the Araceae family, all members of which bloom on upright spadixes surrounded by a specialized leaf called a spathe. Peace lilies are forest-floor tropicals, hardy only in U.S. Department of Agriculture plant hardiness zones 10b or 11 through 12. They contain calcium oxalate, a toxic substance that can irritate tissues and act as a poison when ingested; their sap also can irritate skin.
Each spadix that stands from the base of the spathe contains dozens of tiny flowers that bloom and pollinate during a 10-day period. After that time, the spathe gradually yellows or develops a green color. After about one month, the spathe, spadix and stem dry and turn brown. Most greenhouse-grown peace lily cultivars are sterile and do not set fruit.
Trim each dead spathe down to its base, near the plant's crown, which is where the above-ground stems and roots join. Trim ragged leaves as you would spaths to improve the look of the plant and make it less tempting to small animals or children. Before and after trimming, clean the scissors, hand pruners or other pruning tool with soap and water, and then wipe the tool with a solution that is one part rubbing alcohol and one part water.
About Gibberellic Acid
Peace lily cultivars such as "Clevelandii," (Spathiphyllum x "Clevelandii") bloom once, like their ancestors. Florists who want to "force" blooms at times other than late winter or early spring use a hormone treatment, called gibberellic acid, that results in blooms within two months on plants younger than the normal maturity of 12 months. Before wresting a bottle of gibberellic acid out of a florist's hands, though, consider not only the expense of chemical treatment but also that the procedure may cause distorted flowers and leaves. The material is also slightly irritating to the eyes of certain individuals and requires the use of personal protective equipment.
Peace lilies initiate bloom during the short days of winter and bloom as days get longer. They bloom best with bright light, although direct sunlight scorches their foliage and flowers. Use some of the newer "multi-seasonal" peace lily cultivars, such as "Connie," "Little Angel" or "Mini," that have a tendency to bloom sporadically over a longer period, extending the spring bloom of traditional cultivars and hybrids. Give them plenty of bright light near, but not in front of, windows.
About Temperature and Humidity
Encourage a long bloom period once you've found peace lily cultivars that bloom at varying times by giving the plants conditions close to those on the rainforest floor. Winter temperatures of 60 to 65 degrees Fahrenheit help initiate strong blooms, and spring temperatures from 70 to 75 degrees Fahrenheit encourages sustained bloom. Moist soil provides humidity. So water each peace lily's soil until the water runs out the plant pot's bottom drainage holes, and then allow the soil to become almost dry before watering again. Constantly wet soil or a pot left sitting in water encourages root rot.