Oxalis, a member of the wood sorrel family, often gets a bad rap because of its weedy reputation. While it’s true that some native species can quickly overrun a lawn or garden, there are many ornamental varieties that are well-behaved and full of charm. With colorful clover-like leaves and dainty flowers, oxalis are superb accent plants in garden beds and containers. Many oxalis are also perfectly happy as house plants, especially in areas with colder winters.
I. Appearance and Characteristics
Oxalis ( (American English) or (British English)) is a large genus of flowering plants in the wood-sorrel family Oxalidaceae, comprising over 550 species. The genus occurs throughout most of the world, except for the polar areas; species diversity is particularly rich in tropical Brazil, Mexico, and South Africa.
Many of the species are known as wood sorrels (sometimes written “woodsorrels” or “wood-sorrels”) as they have an acidic taste reminiscent of the sorrel proper (Rumex acetosa), which is only distantly related. Some species are called yellow sorrels or pink sorrels after the color of their flowers instead. Other species are colloquially known as false shamrocks, and some called sourgrasses. For the genus as a whole, the term oxalises is also used.
These plants are annual or perennial. The leaves are divided into three to ten or more obovate and top-notched leaflets, arranged palmately with all the leaflets of roughly equal size. The majority of species have three leaflets; in these species, the leaves are superficially similar to those of some clovers. Some species exhibit rapid changes in leaf angle in response to temporarily high light intensity to decrease photoinhibition.
The flowers have five petals, which are usually fused at the base, and ten stamens. The petal color varies from white to pink, red or yellow; anthocyanins and xanthophylls may be present or absent but are generally not both present together in significant quantities, meaning that few wood-sorrels have bright orange flowers. The fruit is a small capsule containing several seeds. The roots are often tuberous and succulent, and several species also reproduce vegetatively by production of bulbils, which detach to produce new plants.
Tuberous woodsorrels provide food for certain small herbivores – such as the Montezuma quail (Cyrtonyx montezumae). The foliage is eaten by some Lepidoptera, such as the Polyommatini pale grass blue (Pseudozizeeria maha) – which feeds on creeping wood sorrel and others – and dark grass blue (Zizeeria lysimon).
II. How to Grow and Care
Growing conditions differ among the numerous species in this genus. One of the best ways to learn how to care for an oxalis is to research its origin for information on its natural habitat. Then you can understand its proper growing conditions. Some oxalis are alpine plants, woodland plants, or tropical plants, each with different needs.
Sunlight
The amount of sun exposure depends on the species. Tropical plants hardy in USDA zones 9 to 10 will tolerate more direct light. Most species grown in zones 5 to 8 thrive best with bright indirect light in the morning. All species benefit from afternoon shade. Heat generated by too much sun is more likely to cause poor performance.
Temperature and Humidity
Ideal temperature and humidity levels are species dependent with tropical varieties more tolerant of heat. For other Oxalis, including houseplants, temperatures between 60 and 75 degrees Fahrenheit are adequate. You may need to provide additional humidity for tropical species grown as houseplants. Most are frost tender with foliage turning brown and dying back around 50 degrees Fahrenheit. Winter protection may include digging and storing the corms.
Watering
Oxalis responds best to conditions on the dry side and quickly declines in soggy soil. Water every 1 to 2 weeks except in cases of extended heat. Tropical species may need water more often. Most Oxalis, garden-grown and houseplants, enter a period of dormancy in late summer or early autumn. Watering during dormancy rots the resting corms, so withhold water until new growth begins again in late winter and early spring.
Soil
Plant Oxalis in a location with fertile, well-draining soil with a slightly acidic pH. Garden plants benefit from compost added to the soil. Houseplants thrive in a mix of indoor potting soil with added sand or grit.
Fertilizing
Fertilize oxalis plants monthly during the growing season (spring and sometimes fall). Do not fertilize during a period of dormancy or during the winter. Use a fertilizer with a 10-10-10 NPK ratio, either in slow-release granular form in the garden or as a liquid flower fertilizer, following the product instructions, for indoor plants.
Planting Instructions
Spring is the best time to plant oxalis. Loosen the soil and amend it with compost to provide excellent drainage for nursery plants or bulbs. If you are planting rhizomes or bulbs, plant them only 1.5 inches deep. If you are planting nursery-grown plants, dig a hole slightly larger than the nursery container. Remove the plant from the container and plant it at the same depth in the hole. Backfill, pressing down on the soil with your hands to remove air bubbles. When planting multiple plants, check the plant nursery tag for spacing recommendations.
Pruning
After flowering or in lieu of flowering, most Oxalis enter dormancy in late summer or early autumn. Remove foliage which has turned brown and died back. Deadhead spent flowers by removing the entire stem at the base.
Propagation
Oxalis corms multiply rapidly making this plant easy to divide when new growth emerges in early spring. To propagate through division follow these steps:
- Gather a garden spade, fork, or shovel and sterile cutting tool.
- Use the fork or spade to dig around the outside circumference of a clump of Oxalis. Dig down 8- to 10 inches to remove corms and roots. Lift out the clump and remove as much soil as possible.
- Corms may pull apart easily or can be cut to separate them. Each needs to include roots and the start of a green shoot.
- Plant divided corms just below the soil level in a new location.
- Water well and allow the soil to dry between subsequent waterings.
Potting and Repotting
To transplant an individual seedling into a pot, fill a deep container 5 inches in diameter with a mix of potting soil and sand or grit. Place the seedling in the middle of the pot with the crown slightly above soil level and water thoroughly.
Potted Oxalis should be divided annually or moved into a container 2 inches larger in diameter. Remove the plant from its original pot using a garden trowel or your hands to lift it. Replant the Oxalis in a larger pot while adding and tamping down the soil and water well.
Overwintering
In temperate zones, Oxalis grown outdoors in pots can be brought indoors when night time temperatures drop below 50 degrees Fahrenheit. Keep potted plants in an unheated basement or garage and allow them to go dormant. Remove leaves that have died back and withhold water and fertilizer.
Garden plants perennial to your growing zone can be pruned back to ground level in autumn. For perennial species grown outside their hardiness zone, dig corms in autumn. Place the corms in a container with moistened sphagnum moss and store them in a cool dark location until they can be planted out the following spring.
Houseplants need a one to three month rest period. After the foliage dies back, place the pot in a cool, dark room and withhold water and fertilizer. After the required dormancy period, return the Oxalis plant to receive bright, indirect light, and resume seasonal maintenance.
Pests and Diseases
Common Pests and Plant Diseases
Oxalis attracts spider mites and leafminers which can damage the appearance of the foliage. Apply neem oil as a preventive or in severe cases treat with a pesticide listed specifically for leafminers.
Fungal infections including mildew, leaf spots, and rust can affect Oxalis and can be treated with fungicides.
Common Problems
Most problems occur due to inadequate environmental conditions or maintenance errors.
Failure to Bloom
A period of dormancy is key to getting Oxalis to bloom. Chances of flowers improve when the species selected are hardy in your growing zone.
Leggy Appearance
Move the plant to a location where it receives better light or remove adjacent foliage that may be shading it.
III. Uses and Benefits
- Culinary uses
Wood sorrel (a type of oxalis) is an edible wild plant that has been consumed by humans around the world for millennia. In Dr. James Duke’s Handbook of Edible Weeds, he notes that the Native American Kiowa people chewed wood sorrel to alleviate thirst on long trips, the Potawatomi cooked it with sugar to make a dessert, the Algonquin considered it an aphrodisiac, the Cherokee ate wood sorrel to alleviate mouth sores and a sore throat, and the Iroquois ate wood sorrel to help with cramps, fever and nausea.
The fleshy, juicy edible tubers of the oca (O. tuberosa) have long been cultivated for food in Colombia and elsewhere in the northern Andes mountains of South America. It is grown and sold in New Zealand as “New Zealand yam” (although not a true yam), and varieties are now available in yellow, orange, apricot, and pink, as well as the traditional red-orange.
The leaves of scurvy-grass sorrel (O. enneaphylla) were eaten by sailors travelling around Patagonia as a source of vitamin C to avoid scurvy.
In India, creeping wood sorrel (O. corniculata) is eaten only seasonally, starting in December–January. The Bodos of north east India sometimes prepare a sour fish curry with its leaves. The leaves of common wood sorrel (O. acetosella) may be used to make a lemony-tasting tea when dried.
- Ornamental uses
Several species are grown as pot plants or as ornamental plants in gardens, for example, O. versicolor.
Oxalis flowers range in colour from whites to yellow, peaches, pink, or multi-coloured flowers.
Some varieties have double flowers, for example the double form of O. compressus. Some varieties are grown for their foliage, such as the dark purple-leaved O. triangularis.
Species with four regular leaflets – in particular O. tetraphylla (four-leaved pink-sorrel) – are sometimes misleadingly sold as “four-leaf clover”, taking advantage of the mystical status of four-leaf clover.
