A stemless herbaceous perennial native to Central America's highlands, Oxalis deppei -- with botanical synonym Oxalis tetraphylla -- grows 6 to 9 inches tall. More commonly called the good-luck plant or iron cross oxalis, it displays four triangular leaflets on each compound leaf. Each green leaflet displays a dark purple band or wedge at the base. In late spring to midsummer, the good-luck plant bears a stems topped with a loose cluster of flowers. The blossoms look dark rosy magenta, each with a green-yellow throat.
Often the good-luck plant is sold in small containers at garden centres to celebrate St. Patrick's Day. If you garden in U.S. Department of Agriculture Plant Hardiness Zones 8 through 10, you can transplant the good-luck plant into the garden. It will naturalise and return year after year. In the West, where great variation exists in elevation, gardeners often use the Sunset climate zones for plant hardiness. Using this climate zone system, good-luck plant is hardy outdoors in Zones 7 through 9 and 12 through 24.
Plants grow from small bulbs. Gardeners can purchase and plant bulbs or transplant growing specimens nursery containers. Plant them in fertile, loose-textured garden soil that is rich in organic matter such as compost, decomposed leaves or manure. The soil should not compact or become bone dry or flooded. An evenly moist but well-drained soil is ideal.
Gardeners have two options for growing the good-luck plant: indoors or outdoors. If grown indoors as a houseplant, position the container so it receive bright, indirect light. An eastern window provides gentle direct rays at sunrise. Do not place in a hot, sunny southern- or western-facing windowsill. Outdoors, plant good-luck plant in dappled sunlight, as under the open branches of an overhead tree or arbor. If soil remains evenly moist and temperatures don't get above 29.4 degrees Celsius, partial sunlight is acceptable. Don't expose the plant to more than four to six hours of direct sun rays, and none during the heat of midday.
Subfreezing temperatures kill back foliage over winter, but the plant rejuvenates in spring. Once leaves are present from spring to early fall, water to keep the soil evenly moist, supplementing rainfall as needed. When the plant is dormant in winter, keep the soil barely moist. Overwatering from fall to early spring encourages bulb rot and fungal maladies. When the plant displays leaves, apply a liquid fertiliser once per month. Follow product label directions for dosage and formulation.