Mimosa pudica, also known as sensitive plant or sleeping grass, is a small, short-lived, perennial most valued for its interesting foliage. The plants are not tolerant of cold temperatures and die back when exposed to frost. In the United States, Mimosa pudica is grown most frequently as a houseplant, where its growing environment can be strictly controlled, or as an outdoor annual. In tropical climates, the plant may become weedy or invasive when not controlled.
Native to Brazil and other areas of South and Central America, Mimosa pudica grows wild in places with moist, rich soil and warm temperatures, usually in lawns and open fields, and along roadsides, ditches and thickets. The plant forms a thick ground cover when allowed to spread and prevents other plants from reproducing, which has led to its label as an invasive species in tropical areas outside its natural habitat.
Mimosa pudica is an evergreen sub-shrub that reaches no larger than 5 feet in height and produces small, globe-shaped flowers in summer. The plant's most fascinating feature is its fern-like leaves that close and fold up when touched. This reaction is known as a seismonastic movement, or a physical reaction to shock. At night, the leaves also close as a reaction to the absence of light, which is known as a nyctonastic movement. The plant's common name derives from this sensitivity to outside stimuli.
Most commonly grown in homes and gardens for ornamental purposes and as a curiosity, Mimosa pudica also has potential medicinal benefits. Although further research is needed, the plant contains an alkaloid known as mimosine, which is an iron chelator. According to a 2005 study published in the Journal of Clinical Oncology, mimosine has a potent cytotoxic effect on ovarian cancer cells in both rats and humans.
Mimosa pudica requires full sun to partial shade and rich, moist, well-drained soil to thrive. When growing in containers, a soil mixture made of two parts peat moss, two parts loam and one part sand is recommended to provide adequate drainage and fertility. Weekly watering keeps the soil moist but not soggy, which sensitive plant prefers. Plants benefit from weekly fertilizing during the spring and summer months using a balanced fertilizer diluted to half-strength, but feeding should be reduced to one per month during winter. Mimosa pudica needs warm growing conditions and temperatures should not drop below 65 degrees Fahrenheit or yellowing of leaves and stems may occur.
Mimosa pudica is best propagated from seed. For the best results, soak seeds in warm water overnight or until they become swollen, and sow immediately in seed-starting soil mix, covering with soil two to three times their thickness. Keep the growing medium moist at all times. Do not over-water or allow it to dry out completely. Place in bright light and wait for germination, which takes two to three weeks at 70 degrees Fahrenheit. Transplant into pots when seedlings reach about 4 inches in height, and resume regular care for the remainder of the plant's life.