With its stunning and eye-catching purple foliage, Oxalis triangularis or Purple Shamrock is sure to be the star of the show wherever placed indoors. Provided the proper indoor growing conditions, it will provide you with robust growth and color throughout the seasons. Below is a quick summary of its care.
I. Appearance and Characteristics
Oxalis triangularis, commonly called false shamrock, is a species of perennial plant in the family Oxalidaceae. It is native to several countries in southern South America.
Growing to 50 cm (20 in) tall and broad, the subspecies O. triangularis subsp. papilionacea, the purple leaf false shamrock, is hardy in mild and coastal areas of Britain, down to −5 °C (23 °F), and has won the Royal Horticultural Society’s Award of Garden Merit. It is a perennial plant without aerial stem, formed by leaves borne by a long petiole emerging at the ground level of a tuberous rhizome (5 cm long, over 10 – 15 mm in diameter, fully covered with scales). The leaf is formed of three sessile leaflets, triangular to ovate-triangular, glabrous, arranged in the same plane perpendicular to the petiole.
The five densely haired sepals are 5 to 5.5 mm long, narrow and slightly reddish at the top. The five white petals are about 2 inches long and oblong-lanceolate. The stamens and the style are densely hairy. The limb of the wild species is green but purple cultivars have been selected for horticulture. The petiole, soft, whitish, is 15 to 25 cm long. Flowering takes place from spring to autumn.
The leaves of O. triangularis move in response to light levels, opening in high ambient light (in the day) and closing at low light levels (at night). During this movement, the leaflets fold at the level of the central vein. This movement is not due to growth and is instead powered by changes in turgor pressure in cells at the base of the leaf. It is an example of photonasty.
II. How to Grow and Care
Sunlight
For the best growth, place your Purple Shamrock in an indoor location that receives bright light. If indoor light conditions are too low, the plant’s growth won’t be as robust and it will have a tendency to become leggy.
If you notice this becoming a problem with your Purple Shamrock, just move it to a brighter location. If you desire to give your plant a break from indoor growth, place it in a partially sunny outdoor location and not in full sun. Although it grows best in a bright location indoors, the window reduces some of the sun’s rays and if the location outdoors is too sunny, the leaves can burn.
Watering
Your Purple Shamrock will be more forgiving if you forget to water than if you water too much, which leads to soggy soil conditions and problems with rot. Constantly wet conditions can end up killing your plant, so it’s imperative to water properly.
- During the growing seasons of spring through summer, water when the top inch of soil feels dry.
- During the dormant season of fall and winter, water about every two to three weeks.
It is easy to check if your Purple Shamrock needs water by sticking your finger into the soil. If the top inch or so feels dry to the touch, apply water until it runs from the pot’s bottom drain holes.
During the dormant season, the plant has suspended its growing so it does not require the amount of water it needs while actively growing. When watering, use room temperature water and not water that is too cold.
Soil
Oxalis triangularis performs well when grown in standard potting mixes that drain well. The bulbs or fibrous roots will rot if planted in soils that are too heavy and retain too much water.
For the best results, use a rich, lightweight potting mix with or without the addition of a slow-release fertilizer. The addition of a fertilizer into the potting mix only means you will not have to worry about fertilizing as frequently as you would with mixes lacking the addition of the fertilizer.
Many types of potting soil are too heavy and don’t drain properly, which can lead to problems with rot. However, if that is what you have on hand you can lighten the mixture before planting your Purple Shamrock. Some soil mixture suggestions include:
- Mix one part potting soil with one part potting mix
- Mix one part potting soil with one part peat
- Mix one part potting soil, one part potting mix, one part peat
Whatever mixture you decide to use to grow your Purple Shamrock, the biggest thing to remember is the soil needs to drain properly and not retain too much water. If after you water you notice the water remains on top of the soil, draining slowly, the mixture is too heavy and needs to be lightened.
Fertilizing
Like watering, you only have to worry about feeding your Purple Shamrock while it is actively growing in spring through summer. Stop feeding in fall and winter when the plant goes into dormancy.
If your potting mix contains a slow-release fertilizer, which continues to feed the Purple Shamrock for up to three months, you won’t have to worry about additional feedings for several months. If you choose to continue feeding using a slow-release blend, scatter the granules over the soil and water well after applying.
Otherwise, use a water-soluble blend for houseplants applied when you water. To keep your Purple Shamrock looking and growing its best, fertilize every two to three weeks.
Salts can build up in the soil after continued fertilizer applications, which can result in burned foliage so the soil requires periodic flushing. Take your container to the sink and allow water to run slowly through the soil for about five minutes.
This should remove the unwanted salts from the soil. Once the container drains, move it back to its indoor location. You will probably only have to flush the soil of the unwanted salts about every four to six months.
Pruning
Other than to pinch off any dead foliage, especially as the plant goes into dormancy, the pruning requirements for Purple Shamrocks are low to none.
Propagation
Oxalis triangularis is propagated by separating the offsets to create additional plants. This is best done while the shamrock is in its dormant stage. Remove the Purple Shamrock from its container and gently pull the bulbs apart. Once separated, you can plant the bulbs in new containers.
Before you consider repotting or separating offsets, make sure to allow the foliage to die naturally and don’t trim it off too soon and while it still has color. The bulbs are still gathering nutrients from the foliage and cutting it off too soon can lead to weaker bulbs that don’t perform as well when replanted.
Care Through Dormancy
Do not be surprised if you start noticing the leaves on your Purple Shamrock starting to brown and become dry after several months of growing strongly. This is the plant entering a period of dormancy, which normally happens in summer, and is a chance for the corms to rest and recharge before another period of growth.
Dormancy can be a little unpredictable indoors, and sometimes the plant will have several cycles of strong growth, followed by die back during the year. Dormancy can also be triggered by temperatures higher than 80°F (27°C).
When the foliage starts to turn brown and die back, cut back on watering and allow the affected leaves to dry out, before pruning them off. Move your plant to an area that is cool and dark for 2-4 weeks to allow the plant to rest.
After this, move the pot back to a brighter location. Commence normal watering and fertilize the plant to stimulate new growth and your plant should bounce back stronger than ever.
Repotting
The plant only requires repotting every few years to add fresh soil or to create new plants from the additional offsets produced. Move up to a container that is one size larger if you aren’t separating the offsets and are just refreshing the soil.
The best time to repot is in winter during the plant’s dormant stage. Just follow the same instructions as for planting new bulbs.
Pests and Diseases
Common Pests
When it comes to possible pests on your indoor Purple Shamrock, the two biggest threats are spider mites and mealybugs. In severe cases of infestation and if left untreated, both pests can kill your Purple Shamrock plant, as well as spread to your other houseplants, so quick treatment is advised. Identifying both pests is easy.
- Mealybugs: Mealybugs show up on the Purple Shamrock as masses of a white cottony substance, which are actually groups of the pests. They suck out the plant’s juices and can weaken or kill it.
- Spider Mites: Spider mites are tiny, sap-sucking insects that spin a fine webbing over the Purple Shamrock. Like mealybugs, an untreated infestation can weaken or kill the plant.
Treat both pests by spraying both sides of the foliage and all other areas of the Purple Shamrock with an insecticidal soap or neem. Repeat the treatment as directed on the product’s label.
Common Diseases
For the most part, Purple Shamrock plants are relatively free of serious disease problems. However, overwatering or growing it in too soggy conditions can cause problems with rot.
When rot is the problem, the underground bulbs turn black and mushy and the entire plant eventually collapses and dies. When this happens, it’s best to just discard the plant and start with a fresh one, watering when the top inch of soil becomes dry and being sure to grow the shamrock in soil that drains well.
The other two problems that can affect Purple Shamrock plants are the fungal diseases powdery mildew and rust. These problems usually occur when temperatures are cool, there is too much humidity and the plant isn’t getting adequate light. Both problems are easy to identify.
- Powdery Mildew: Powdery mildew shows up on the plant as powdery white patches that affect all portions of the shamrock including the blooms. In severe cases, the powdery substance can coat the entire plant.
- Rust: Rust shows up as small, light yellow flecks on the foliage, as well as a white powdery substance covering all portions of the plant.
Most of the time these problems aren’t severe and rarely require treatment, other than moving the plant to a bit warmer and brighter location, if possible and decreasing the amount of humidity. However, if the problem is growing you can spray the Purple Shamrock with a fungicide, repeating as suggested on the product label.
III. Uses and Benefits
The leaves are eaten raw or cooked and have an acidic taste due to their oxalic acid content. Leaves and flowers can be used as a decoration for salads. When consuming larger amounts of leaves, the oxalic acid can cause discomfort. The rhizomes are eaten raw or cooked and have a sweet taste.
