My own plant by the end of May 2014

I decided to write about purple shamrock simply because I have one on my windowsill right now. It is not commonly seen in the market, as bulb division is the only way it reproduces itself. Nevertheless I feel it deserves more attention – how can you refuse such a pretty little thing that’s so easy to take care of?

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Description

Purple shamrock is a seemingly delicate, yet quite adaptive and low-maintenance bulbous member of the genus Oxalis (commonly known as wood sorrels).

It is grown for its foliage color and especially suitable for planting in a small clay pot as a lovely gift — its heart-shaped leaflets got it another nickname ‘love plant’. You can also use it for bedding or as part of a container combo.

With no viable seed production, it replicates itself by steady bulb multiplication, usually in the fall.  Given enough time it can form a dense clump or mat without any risk of getting invasive.

Purple shamrocks are quite forgiving as long as you provide them with well-drained soil and adequate sunlight to maintain its leaf color. Take care, though, that plants with limited moisture supply can get burned under hot summer sun. The plants can be cut back to the soil line and regenerated should they get leggy and wimpy after a long summer.

Some of them may go dormant briefly when it is too warm (>80 ^°F or 27 ^°C) and push up new growth again with the falling temperature. Most would go dormant again in the winter. If they are planted out, you can dig the bulbs up after foliage fades and store them in an empty pot for planting next spring, or leave them in the ground and expect a few to come back (not quite reliable). While in a greenhouse setting, they may keep growing and flowering all year long, but it is generally believed that the occasional dormancy can help it grow more vigorously.

To add more interest:

1. It is edible

The leaves and flowers have a sour taste similar to lemon. It tastes just like other wood sorrels, if you have ever tried some. These plants contain relatively high amount of oxalic acid, a common acid also found in spinach (this acid is first isolated from Oxalis, hence its name), so make sure not to consume too much.

2. It can dance

The leaves open up during the day and close at night. Its flowers open with the rising sun and close with sunset. Scientifically this is known as ‘nastic movements’. (What a strange name though…

Sometimes when the sun is blazingly hot, the leaves will also drop in response. I guess that is a protective mechanism.

You can learn more at http://en.wikipedia.org/wiki/Nastic_movements

(there’s even a video clip illustrated with purple shamrock) Link to the video

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Key characteristics

Name: Oxalis triangularis (synonym: Oxalis regnellii, Oxalis atropurpurea)

– original plants seem to grow green leaves as well. a few cultivars are green too

– there are some confusion with the scientific names, but Oxalis triangularis is official

Common name: False shamrock (usually refers to the varieties with green leaves); Purple shamrock; Love plant

Growth habit: Bulb (scaly rhizome-like) with periodical dormancy

Origin: South America (Brazil etc.)

Other traits: Edible

Plant habit:

• Height: 4-12 inches
• Exposure: Full sun to bright shade
• Hardiness: USDA Zone 6-10
• Foliage: Red/purple clover-shaped
• Flower: Delicate pastel pink flowers, each open for one day
• Blooming time: Summer months

Notable cultivars:

Usually people don’t care that much about specific varieties of this plant. Though a few established cultivars are commonly seen: Oxalis ‘Francis’, Oxalis ‘Atropurpurea’

A new variety ‘Charmed Wine’ seems to be quite nice too: Click for pictures

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Cultivation

Light:

Try to place/plant it somewhere in bright sunlight without getting too hot. Without adequate light, the leaf color won’t be as attractive and it is prone to grow long long necks.

Water:

Purple shamrock has moderate water needs, which means it can make do with a little too much or too little. However the bulb would certainly rot if allowed to stand in water for long.

Reduce/stop watering once the plant shows signs of dormancy and resume when new growth emerges.

Soil:

Anything is fine other than heavy sticky clay that takes ages to drain.

Temperature:

Ideally between 60-80 °F/15-27 °C, it will go dormant if it gets too hot or too cold.

Fertilizer:

Feed sparingly. Use one high in phosphorus and potassium as they are good for bulb growth. Too much nitrogen will render the leaves green.

Pruning:

Pulling the dead leaves and faded flowers away are quite easy. Give it a ‘haircut’ if the growth becomes unruly.

Special notice:

If you decided to dig up the plant to store the bulb or divide the plant for give-away, do it in the fall when the leaves start to decline. You’ll find plenty of plump bulbs hiding beneath the soil. They can be kept at 30-50 °F/0-10 °C for months. Just try not to let the bulbs dry out completely.

Propagation:

Dig up bulbs and plant separately.

(this picture is from flickr user effika, under creative commons license)

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Related species

Oxalis is a big genus containing many exciting species for gardeners, and plenty of weeds as well 😦

One way to divide them is quite simple: non-tuberous and tuberous.

• The non-tuberous species tend to be weedy. E.g. Oxalis corniculata( creeping wood sorrel) and Oxalis stricta (yellow wood sorrel).

Click to see pictures of the common weedy oxalis

• While many of the tuberous species are commonly cultivated. Some notable examples include: Oxalis versicolor (candycane sorrel), Oxalis purpurea (purple wood sorrel), Oxalis pes-caprae (bermuda buttercup), Oxalis obtusa (yellow-eyed sorrel), Oxalis hirta (hairy sorrel), Oxalis glabra (finger-leaf), Oxalis bowiei (cape shamrock), etc.

Click to see pictures of the common ornamental species

However, according to molecular taxonomy, Oxalis triangularis belongs to a small clade lied right between the non-tuberous and tuberous group. It fits in the section “Pseudobulbosae”, which stands for “false bulb”. The most closely related species are Oxalis latifolia and Oxalis tetraphylla. The three of them form an interesting trio that I’ll briefly explain and compare in the following session.

Alternatively, the genus can be divided into (South) African species, American species and others (incl. cosmopolitan ones that tend to be weedy). Most ornamental species are from southern Africa, while a few are from America. Interestingly, our trio – Oxalis triangularis/latifolia/teraphylla are all American species.

Oxalis latifolia (broadleaf wood sorrel)

This plant is originally from Mexico and other central/southern America countries. There are a range of sub-species with widely different habitats, thus the plant itself tends to be quite variable. The leaf lobes can be wide or narrow and the flower color can be anything from white to deep pink. They replicate by both seeds and rhizome-end bulbils. Unfortunately, such great adaptability means that broadleaf wood sorrel is considered a noxious weed & invasive species in many places.

 

Oxalis tetraphylla

• Tetraphylla means “four leafs”, and it is also known as “lucky clover”.
• One of the most common species in cultivation due to the famous cultivar “Iron Cross”, also known as Oxalis deppei
• Its growth habit is quite similar to that of purple shamrock, but can be less uniform & more delicate. I will not run into details about the cultivation of .tetraphylla here.
• A few key differences: 1. It is more fussy about light. Too much light will make it very wilt, while too little can produce floppy plants that collapse to one side (taller and weaker stems than .triangularis). 2. It is less hardy than purple shamrock. Better dig them up and store the bulbs indoors.
• Generally speaking it is also an Oxalis species with stunning foliage and easygoing nature.