How to Grow and Care for Oxalis

Grown in the garden or occurring naturally, the genus Oxalis, Oxalis spp. is made up of long-stemmed diminutive plants recognized for their unique leaf forms. Depending on the species, foliage may consist of three to five leaves, often notched in the middle, resembling clover or butterfly wings.

Its leaves also have the unusual habit of opening during the day and folding closed at night. Commonly called Shamrocks, the species Oxalis triangularis often appears as a foliage plant offered at garden centers around the annual St Patrick's holiday in early March.

With more than 550 species, Oxalis is grown both as a houseplant and garden plant, annual or perennial depending on your growing zone. Although it requires specific conditions to flower, blooms cover the color spectrum from white to yellow and shades of red, pink, and purple. Foliage can be variegated or solid green to deep purplish red.

Some species grow from corms that multiply forming mounds and subshrubs. Other species have a creeping habit and spread through rhizomes as potential ground covers. Oxalis is toxic to dogs, cats and horses.

How and When to Plant Oxalis

Oxalis grows best in areas with cool summers and mild winters. In regions where summers are hot, plant in a north-facing location that receives afternoon shade. If your winters are wet, plant in raised beds or rock gardens.

Corms can be planted in pots or trays in autumn to keep as houseplants or as starts for the spring garden. Plant corms or transplants outdoors in May.

Corms are long and narrow, rounded at one end and tapered at the other. Plant them vertically with the narrow end pointing up. They can be cut in half with the bottom half planted cut side up. In the garden, space corms 3- to 4-inches apart and 1- to 1 1/2-inches deep. Allow 4 to 10 inches between transplants.

Corms grown as houseplants can be started in shallow pots with well-draining, indoor potting mix. Space them 1-1/2 inches apart and deep. Place pots to receive bright light and water sparingly until new growth appears. Corms multiply rapidly and you'll want to pot up into a deep pot 10 inches in diameter with drainage holes.

Oxalis Plant Care

Different Oxalis species are found naturally in woodlands, high elevations, and the tropics. Woodland species adapt more readily to average garden conditions whereas tropical and alpine varieties need more specific environments and care. Creating conditions similar to the native habitat where your chosen species is found gives the best results.

Light

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.

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.

Water

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.

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.

Fertilizer

Oxalis gains the most benefit from soil enriched with compost and organic nutrients. Alternatively, apply an inorganic NPK 10-10-10 or 5-10-10 slow-release fertilizer at the start of the growing season. Fertilize houseplants monthly with a diluted, liquid, and all-purpose houseplant food. Discontinue feeding for all types during dormancy.

Types of Oxalis

• Purple Shamrock, Oxalis triangularis: This species is most often sold as a foliage houseplant. Small umbels of white or pink flowers above purple foliage resembling butterfly wings. Hardy in USDA zones 6 to 11.
• Candy Cane Sorrel, Oxalis versicolor: Perennial bulbs form mounds of narrow, green, and clover-like foliage. Flowers are 1-inch white blooms featuring red stripes on the undersides of petals. Hardy in USDA zones 7 to 9
• Tropical Woodsorrel, Oxalis hirta: Blooms in autumn through spring with vivid pink flowers on upright, branching, stems. Clusters of green leaflets are oblong. Hardy in USDA zones 9 and 10.
• Redwood Sorrel, Oxalis oregana: A creeping, groundcover perennial with 1-inch white or rose pink flowers with yellow centers and lavender veining on green clover-like leaves. Hardy in USDA zones 7 to 9.
• Silver Shamrock, Oxalis adenophylla: Features 1-inch white flowers with dark purple centers and veining on a background of heart-shaped gray-green leaves. Hardy in USDA zones 4 to 9.

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.

Propagating Oxalis

Oxalis corms multiply rapidly making this plant easy to divide when new growth emerges in early spring. To propagate through division follow these steps:

1. Gather a garden spade, fork, or shovel and sterile cutting tool.
2. 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.
3. Corms may pull apart easily or can be cut to separate them. Each needs to include roots and the start of a green shoot.
4. Plant divided corms just below the soil level in a new location.
5. Water well and allow the soil to dry between subsequent waterings.

Potting and Repotting Oxalis

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.

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.

How to Get Oxalis to Bloom

For Oxalis to bloom, it has to go through a period of dormancy. Whether grown inside or in the garden, once the foliage dies back, water and fertilizer need to be withheld for the amount of time appropriate for the species. Letting your Oxalis houseplant become slightly rootbound can also encourage blooming.

Planting a species native to your growing zone also increases the potential for flowering. Oxalis adapts to soil type but can be finicky about sun exposure, heat level, and moisture.

What Do Oxalis Flowers Look and Smell Like?

Oxalis blooms consist of five ray-type petals with one bloom or bloom cluster for each stem. Colors range from white, yellow and orange, to red, purples and pinks often with a contrasting color in the center or in narrow veins throughout the petals. Some species are highly fragrant.

Common Problems With Oxalis

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.