The plant genus Oxalis includes about 800 different species from around the globe, most of these from South America or coastal South Africa. Many oxalis plants "move" in response to the environment, opening and closing both leaves and flowers in response to changes in light, temperature and water stress. Widely known as shamrock plant, good luck plant and wood sorrel, oxalis generally forms small, neat mounds of four-part leaves standing 4 to 12 inches tall. Vegetation may be green, grey-green, purple or purple-black, plain or patterned, hairy or smooth. Flower colours range from white, pink, lavender and purple to yellow and red.
Oxalis as Houseplants
Because they generally prefer part shade, oxalis plants do well indoors as houseplants. They're easy-care too. Simply pot them up, add water, place them in moderately bright light and off they go. Plants need well-drained, moist soils and regular light fertilisation. Unlike most potted plants, oxalis will thrive in crowded conditions, so don't repot them too soon. South American species have fleshy rhizomes and South African types grow from bulbs. Both underground root storage systems allow plants to conserve energy and go dormant periodically -- cut back on water and light to induce dormancy -- then spring back to life again later.
Growing Potted Oxalis Outside
Even in otherwise cold climates, potted oxalis can spend summer outdoors. As with any plant, it's important to allow plants to gradually adjust or acclimate to changing environmental conditions, to prevent undue stress and setbacks. Move oxalis houseplants outside into deep shade for just a few hours every day initially, gradually increasing outdoor time and sun exposure. Finding the right location for your oxalis is as much art as science; pay attention to how your plant responds to various placements. An oxalis that would need shade in hot southern climates may do well in nearly full sun in a cool northern climate.
Growing Oxalis Outside
Most oxalis thrive in part shade, preferring well-drained, evenly moist soil. If you have some shady or part-shade areas with the right soil conditions, you can probably grow oxalis outdoors. Most oxalis varieties are not cold hardy and do best in Mediterranean, tropical or subtropical climate zones. Some oxalis, though, are quite rugged, hardy to zones 5 and 6, including strawberry oxalis (Oxalis crassipes), a Southern cottage garden flower, and the tiny rose pink-flowered Oxalis inops (Oxalis depressa). The dramatic Oxalis vulcanicola "Zinfandel," with bright yellow flowers and purple-black foliage, will do fine in full sun, though it doesn't mind part shade.
Outside Oxalis Warning
In mild climates oxalis can spread prolifically -- something gardeners sometimes promote inadvertently. Digging in garden beds can divide rhizome segments or scatter bulbs, whether oxalis is dormant or not, starting many new plants. Mechanical cultivation in areas where there are dormant oxalis can achieve shockingly successful plant dispersal. Grow oxalis only in containers or confined garden beds if madly multiplying plants would be a problem.