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The mariposa lily is a genus of plants containing 60 individual species. Members of this genus, called the Calochortus genus, belong to the Liliaceae plant family. Mariposa lilies are bulbous flowering plants that grow wild in open woodlands and grasslands. As garden and landscape plants, these lily varieties are hardy perennials with striking spring and early summer blooms. Mariposa lily species originate in western United States and Mexico.
Lilies in the Calochortus genus generally grow to about 2 feet (60 cm) tall. The flowers have a cup-like structure similar to the tulip. Flower color varies considerably between species. One of the most coveted features of the mariposa lily is the variety of colors and patterns inside the flowers, on the inner petals and at the base of the bowl-shaped flower structure. The flowers bloom from spring through early summer.
Of the 60 species, there are several varieties commonly grown in gardens and landscaped areas. The butterfly mariposa lily, Calochortus venustus, has large white flowers. As its name indicates, the Calochortus luteus, or yellow mariposa lily, produces yellow flowers with a dark brown center. Calochortus superbus is a California native with white or pale purple petals. The striking intricate patterns inside each flower create a dramatic addition to a flower garden.
The bulbs should be planted in fall before the first freeze. A spot that has loamy or sandy soil with good drainage is ideal, but light clay soil is usually tolerated. The bulbs are more likely to rot in heavy clay soil and in areas that experience periods of standing water. Mariposa lilies should be planted 4 to 6 inches (10 to 15 cm) deep, in clumps. These bulbs grow best in a spot that gets at least six hours of sun per day.
A layer of mulch helps keep mariposa lily bulbs protected over winter. When the ground freezes and thaws, it can heave, exposing the bulbs. The mulch layer acts to insulate the soil, reducing frost heave. The mulch should be spread 4 to 6 inches (10 to 15 cm) deep. Organic mulch material, such as straw, peat moss, wood chips, sawdust and leaf mold, or shredded leaves work well.
The mulch layer can be pulled back in spring to give the bulbs room to grow. Planting the bulbs in fall is important when growing mariposa lilies because it provides the necessary cold dormancy period, and gives the bulbs a chance to establish before the growing season. Once planted, plants typically come back year after year, with little additional care from the gardener.