Dig holes 3 to 4 inches deep in damp soil or boggy soil. Space multiple arum lilies 18 inches apart. Plant arum lilies 12 inches deep or less in the mud at the edge of ponds and water gardens.
Place one section or root, called a cormel, in each hole with the roots down and any green shoots pointing up.
Cover each cormel with 3 to 4 inches of soil and pat the area down gently. Water the soil over each arum lily to a depth of 5 to 6 inches to settle the soil.
Water when the top of the soil feels dry to the touch. Soak the soil 6 to 8 inches deep at each application. If the arum lilies are planted in boggy soil or at the edge of a water garden, no additional water is required.
Spread a 2- to 3-inch layer of seasoned manure or compost in a circular area 8 inches wide around each arum lily to provide additional nutrients. Plants in an aquatic environment do not require additional nutrition.
Cut out the flower stalks at the ground when they turn brown and fade. Cut the whole plant down to 1 inch above the ground in late fall or early winter.