Oxalis triangularis, commonly known as a wood sorrel or purple false shamrock is a really interesting houseplant for its surprisingly purple foliage and the way it responds to light.
The green version is known to many Australian gardeners as Oxalis the weed. But before you turn up your nose at deliberately cultivating a weed in your houseplant jungle, take a look at this purple cousin to the green weed.
Oxalis triangularis is a pretty and easy-to-grow houseplant.
Light – give it as much as you can
The leaves of Oxalis triangularis open or close in response to changes in light levels. They spread and open out in high light and fold down at low light levels. During this movement, the leaves fold at the central vein. This movement is not due to the plant growing, but is an example of photonastic movement. This is where plant structures, such as flower petals or leaves change position based on the intensity or direction of light. It isn’t the same as heliotropism in sunflowers, where the whole flower head will move to follow the passage of the sun.
Oxalis triangularis prefers a location with lots of bright light. I have experimented with it on the west facing wind ledge, and while it did droop a bit during the day with the excessive sun exposure, it bounced back over night. I have also tried it on an east facing window, with just morning sun, and it did ok, but it didn’t grow as rapidly, and the leaves were not as intensely purple.
The Oxalis triangularis I have grown are at their best directly under a grow light, which provides 16 hours of full spectrum white light without the heat.
In the picture above, you can see the Oxalis triangularis is happily sharing space with Philodendron Pink Princess, and two small cuttings of Philodendron Paraiso verde being propagated in LECA: all these plants are enjoying the full light treatment. The grow light was bought at Bunnings for $75.
If your Oxalis triangularis looks spindly and isn’t pushing out new leaves, it needs more light.
Water – provide plenty: but only if it gets lots of light
Three things about this plant will tell you that it wants lots of water: the leaves of the Oxalis triangularis are very thin. The petioles (the long portion that connects the leaf to the underground rhizome – it looks like a stem) are thin. The roots are also very fine. There isn’t much about this plant that looks like it can store a lot of moisture. Considering the amount of light this plant requires, it will therefore be able to process a lot of water. If you grow it in a less bright location, it won’t use as much water.
Heat
This plant is originally from South America, so it prefers indoor temperatures between 15 °C and 25°C. It can look wilted and saggy in higher temperatures. Much cooler or higher temperatures can induce dormancy. If it’s left to dry out too much, it will wilt away and go dormant until ideal conditions recur. Indoors, it probably won’t go dormant and most people prefer to keep their living conditions between 15 °C and 25°C.
Feeding
If you provide lots of light and lots of water, Oxalis triangularis will be growing rapidly. A growing plant is a hungry plant, so I feed mine with half strength Foliage Focus each time I water.
Leave the roots alone!
The Oxalis triangularis will respond in a very dramatic – and very ugly – fashion should you chose to divide the plant. Be prepared for all of the petioles to collapse, go soggy and die. The deep purple tones of the remaining leaves will fade. It will seem to take AGES to recover and look marvellous again – perhaps 3 months. Be sure to provide the usual full light and water regime, and it will produce new leaves from the rhizomes in the pot. Take the duration of crisis collapse into consideration when propagating.
Alternatively, you would do well to just leave the roots alone. When it needs a bigger pot, just carefully slide it out of the old pot, into one only slightly bigger, then add more potting mix around it. Don’t mess with the roots, just pot up the whole intact root mass.
Old leaves
As your plant grows, it will push out new leaves and off load the old. The plant will withdraw all resources from the oldest leaves first. They will go limp, the petiole will shrivel and the purple colour will go dull. If you leave it, the part that is in the potting mix will eventually dry up and no longer be in contact with the surface. THAT is the best time to remove the old leaf. I don’t remove the leaves as they start to wilt – I leave the plant to choose how rapidly or slowly it wants each leaf to die. It also helps you to get used to seeing the odd dead leaf on a houseplant – it’s a natural part of the life of the plant. Don’t panic.
Propagating and dividing
Image: Ohio Tropics.
When repotting, dividing or propagating, unpot the plant and soak it in a bowl of room temperature water to remove the majority of the potting mix. Then gently pull it apart into sections. The roots are very fine, so avoid handling them if you can. You will see a collection of small rhizomes, which will probably be white with orangey-brown scales. This is the food storage for the plant, from which new plants will grow. They can be potted in small pots – don’t have too much spare potting mix around the rhizomes – the mix will stay too wet without leaves to process the water, and the rhizomes will rot.
If you divide the whole plant, and there are still leaves, they will be struggling to survive. Be sure to keep the mix moist, but not as much water as you would for a fully leafy large plant. Wait until the new leaves unfurl and flatten out before you increase the watering.
Flowers – nah, don’t bother
Image: Wikipedia
I always remove the flowers as soon as I see them push through the potting mix. I grow this plant for its foliage, not its flowers, because the flowers aren’t that impressive. The more energy the plant spends on producing flowers, the less it produces new leaves. I want leaves, so the flowers are snipped off at the base.
Time – 2 or 3 years before it’s lush and full
My Oxalis, as a houseplant with ideal conditions of 15 °C and 25°C, lots of light and water, took nearly 3 years to become a fully lush plant. So be patient and don’t touch the roots. I didn’t divide mine until after it really packed out the pot with roots and rhizomes. Messing with the roots will set the plant back.
Other Oxalis plants
If you really take a fancy to this plant, here is a list of all the plants in the genus:
- Oxalis triangularis (Purple false shamrock) – known for its distinctive purple leaves and delicate appearance.
- Oxalis corniculata (Creeping wood sorrel) – a low-growing plant with trifoliate leaves and small yellow flowers.
- Oxalis acetosella (Wood sorrel) – characterized by heart-shaped leaves and white or pink flowers, often found in woodland settings.
- Oxalis deppei (Iron Cross plant) – features green, clover-like leaves with a distinctive dark red or purple marking at the center.
- Oxalis pes-caprae (Bermuda buttercup or Sourgrass) – produces bright yellow flowers and is known for its invasive nature in some regions.
- Oxalis purpurea (Purple shamrock) – displays purple or violet-colored leaves and is similar in appearance to Oxalis triangularis but with different leaf shapes.
- Oxalis articulata (Pink-sorrel or Pink wood sorrel) – characterized by delicate pink flowers and trifoliate leaves.
