Oxalis Triangularis is a popular houseplant choice because it is a distinctive houseplant that enjoys a reliable, prolific growth habit. Easily identifiable thanks to its eye catching purple foliage, when in flower the plant produces delicate small trumpet shaped blooms usually in shades of white or pink.
The largest member of the Oxalidaceae family, contributing about 800 different species to the genus, Oxalis Triangularis originates in South America. Its name, Oxalis is inspired by the presence of oxalic acid in the plant’s foliage. Also known as the flash shamrock or purple shamrock, because its foliage resembles a three leaf clover, Oxalis Triangularis is an increasingly popular St Patricks day gift.
Interestingly the Oxalis Triangularis is nyctinastic. This means that the leaves react to the light, opening in the morning and closing during the evening as darkness falls.
Bright and distinctive, the flash shamrock is one of the easiest houseplants you could ever care for.
A long lived plant, with the right care it can become a living heirloom passed down through the generations of a family. This guide is designed to take you through everything you need to know about caring for this most colorful of houseplants.
Purchasing Bulbs and New Plants
Oxalis Triangularis is often sold as a young plant. When selecting yours try to choose the healthiest specimen possible. Don’t be afraid to inspect the foliage for signs of infestation or disease.
The plants are also sold as bulbs. These are surprisingly small and resemble young pinecones in appearance. Again try to select healthy bulbs that don’t show any outward signs of disease.
False shamrocks are commonly found for sale in garden and DIY stores. You can also purchase the plants and bulbs from plant nurseries.
Planting Oxalis Triangularis Bulbs
Plant in a clean pot that is large enough to hold the bulb and accommodate some new growth. To begin with, the pot should be at least 4 inches wide. It should also have drainage holes in the bottom and be pest and dirt free.
As the plant grows you will need to repot it in a slightly larger container. When repotting don’t be tempted to plant into an overly large container, doing so can cause the plant to enter into transplant shock. Instead, gradually increase the size of the pot each time you repot. With an average growth habit, Oxalis Triangularis requires repotting once every two years. This is best done in the spring, just before any new growth emerges. If you purchase a fully grown plant you may decide to repot it once you get it home. This is often a good idea as store bought plants are often pot bound or sitting in nutrient poor soil.
To plant or repot simply fill a pot, with well draining potting soil. A well draining potting mix is essential, Oxalis Triangularis struggles in overly wet soil. You can work a handful of gravel into the soil to further help improve drainage.
Make a hole in the soil about one to one and a half inches deep. Plant your Oxalis Triangularis bulbs with the scales facing up and firm down the soil. Don’t worry if you get the bulb the wrong way round, new growth will still emerge, it may just take a little longer.
You can either plant one bulb per small pot or plant a cluster in a larger pot. If you are planting a cluster of bulbs, space each bulb about 1 inch apart.
When repotting a false shamrock plant, water the soil well about 24 hours before repotting. Doing so helps to reduce the risk of transplant shock. Carefully remove the plant from its original container, being careful not to damage the root system.
Gently brush away any old soil that is clinging to the root. Make a hole in the soil large enough to hold the root system. Position the plant in the center of the hole and firm the soil down.
Water lightly until new growth appears. This should be in about 6 weeks after planting.
Where to Position Your Plant
Oxalis Triangularis, and it’s close relation the Oxalis Regnellii, are hardy in USDA Zones 8 to 11. However they do best, and are more commonly grown as houseplants.
Place your Oxalis Triangularis in a medium light position. The plants can also be placed in bright filtered light positions but avoid placing them in direct light. Too much, direct light can cause the foliage to burn and wilt. If you do need to place the plant in a bright light position, blinds can be used to provide some shade. A morning light position such as an east facing windowsill is ideal.
As Oxalis Triangularis like to grow towards the light you will need to rotate the plant every 2 weeks. This helps to encourage even, balanced growth.
The room temperature around the plant should average 60 to 70 °F. While the plants can cope with temperatures slightly cooler than this, avoid overly warm temperatures. Placing the plants in a warm position can trigger dormancy. If your home is too warm, there are a number of affordable, easy ways to cool your chosen room down.
Caring for Oxalis Triangularis
Once you find the ideal position, Oxalis Triangularis care is pleasingly easy.
Requiring minimal regular care, you will need to repot every few years to prevent the plants from becoming pot bound.
When to Water
Knowing how often to water a houseplant can be difficult. Allow the soil around your Oxalis Triangularis plant to slightly dry out before you water. Ideally the top half an inch of soil should be dry before watering. If you are unsure, allow the soil to dry out a little more before watering. It is far better to slightly underwater than overwater a plant. A soil moisture meter, such as the Gouevn Soil Moisture Meter, is a useful device if you struggle to know how frequently to water your houseplants.
When you water the plants, use a watering can to evenly soak the soil around the plant. Water until water begins to seep from the drainage holes in the bottom of the pot.
While it varies depending on the age of the plant and the growing conditions, on average you will need to water once every 2 weeks.
During the fall and when dormant the plants require less water than during active growth periods.
Fertilizing your Plant
As the plant matures a slow release fertilizer can be applied once every 4 months. You can also apply a diluted houseplant feed once a fortnight during the growing seasons. As well as chemical solutions there are a number of effective, natural fertilizers that are appropriate for houseplants.
In the late summer, reduce or even cease fertilizing until the next growing season begins.
During the summer months, if the temperature is around at least 55°F, your Oxalis Triangularis can be placed outside in a sheltered condition.
Don’t place the plant in direct sun, this can cause the foliage to become sunburnt.
Remember to check the plant for signs of infestation after you return it inside.
In the summer, the plants can be placed outside to enjoy the warmer temperatures. Remember to return the plant inside before the temperatures fall.
The False Shamrock’s Dormancy Period
Like other bulb plants, Oxalis Triangularis requires a period of rest or dormancy. This occurs naturally in the fall, after the long spring and summer growth period has ended. During the dormancy period the plant stops reacting to the change in light levels and can become less vibrant. Dormancy can also happen if the plant is exposed to temperatures above 80 ℉ for too long or is not watered enough.
Once the foliage begins to wither or die back, cease watering and fertilizing. Allow the foliage to naturally die back. When the foliage is brown it can be removed from the plant.
Wait until the next growth period begins before resuming your watering and fertilizing routine. This could be as quickly as 2 weeks after the plant becomes dormant and is signalled by the emergence of new growth.
Pruning your Plants
Cut away any yellow or shrivelled foliage as soon as you notice it. Keeping a plant neat and tidy helps to maintain good growing conditions and prevent disease. Use sharp, clean garden scissors to make precise incisions. Scruffy, damaged wounds can cause shock or encourage disease to form.
You may also need to hard prune the plants once every couple of years. This means cutting back the foliage to just above the soil line. Hard pruning encourages fresh, vibrant foliage to emerge in the next growing season. Hard pruning is best done in conjunction with separating the tubers.
How to Propagate an Oxalis Triangularis Plant
Tuber division is the preferred method of propagation. This is best done during the dormant winter period. While you can divide the tubers at other times of the year, doing so when the plant is actively growing can increase the rise of transplant shock.
Wait until the tuber, or root, is at least an inch long before you attempt to make divisions.
To divide, remove the plant from the pot and gently brush away any soil from the root system. Use your hands to gently separate the tuber into individual pieces. Aim to divide the tuber into even sections.
Replant each healthy tuber section about half an inch deep in individual pots filled with well draining potting soil. Unhealthy, or diseased sections should be discarded.
Place the newly separated plants in a light position that is slightly cooler than usual. Care for them in the same way that you care for larger Oxalis Triangularis plants. New shoots will appear in the spring.
How to Identify and Treat Common False Shamrock Problems
Oxalis Triangularis plants are surprisingly easy to care for, low maintenance houseplants.
Regularly inspect the foliage for signs of spider mite infestation. Should you notice any pests, gently wipe the accepted leaves with neem oil or warm, soapy water.
Yellowing leaves and mushy stems are often signs of overwatering. Cease watering immediately and allow the soil to dry out before watering again. You may need to repot the plant in better draining soil. When the soil has dried and you are ready to resume watering, apply less water than previously. Remember it is easier to correct the problems caused by underwatering than overwatering.
Underwatering, or exposure to low humidity levels, can cause the leaves to brown and their edges to become crispy. When it comes to humidity levels these are largely unfussy plants. However if you do struggle to maintain humidity levels an easy way to correct this is to place the plants on a humidity tray.
Warning. While the foliage is edible it can cause irritation. Additionally, if ingested in large enough quantities it can be toxic. Keep the plants out of the way of children and pets.
Regularly check the plant’s foliage for signs of disease and infestation.
Attractive and distinctive, Oxalis Triangularis is a pleasingly easy to care for houseplant. Robust and surprisingly durable, the plant’s distinctive foliage and delicate blooms has helped to make it a popular way to introduce color and contrast to your houseplant collection.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.