Surprise lilies reproduce through underground bulbs and must be lifted and divided every two to four years to prevent overcrowding. This is best done immediately after blooming. The bulbs formed inside a papery covering resembling a head of garlic, which must be removed to separate the bulbs. If left to their own devices, surprise lilies may overtake your flower beds, as they tend to spread quickly.
Although surprise lilies are not true lilies, they requires the same soil conditions as other lilies. They prefer loose, well-draining soil with a pH around 6.5, but will tolerate nearly any soil. Adding organic matter to the soil to improve drainage and aeration will improve clay soils and prevents issues arising from soggy soil.
Surprise lilies perform well in either full sun or partial shade but are not otherwise fussy about where you plant them. As long as the area does not remain wet for prolonged periods during the spring, surprise lilies will typically return each year. These hardy bulbs can also be planted in the lawn or under trees.
Individual bulbs should be planted at a depth of 4 to 6 inches in clusters of four to six lilies, spaced 6 to 8 inches apart. Cover the bulbs well with fresh soil and firm it down with your hands to secure the bulb and remove air pockets. Watering to saturate the soil to the level of the bulbs gives your lilies the moisture they need to begin forming a strong root system. Water once or twice a month throughout the fall to encourage good root formation.