How to Grow and Care for Purple Shamrock (False Shamrock)

Purple shamrock (Oxalis triangularis), also known as false shamrock, is one of the uncommon plants with nearly black foliage. In reality, its foliage is a very deep purple color. The leaves are triangular and typically grow in groups of three. At night (or on particularly cloudy days) they fold up almost like an umbrella, but they open again with the morning light. The plant bears tiny flowers that are a white to pale pink or lavender color. Purple shamrock is best planted in the spring and functions well as a houseplant. It has a moderate growth rate. Note that all parts of purple shamrock are toxic to people and pets.

Purple Shamrock Care

The purple shamrock is fairly easy to grow in the ground within its growing zones, as well as in containers and as indoor houseplants. The key to a healthy plant is providing it with a sunny spot and watering it whenever the soil starts to dry out. Also, plan to feed your shamrock throughout its growing season to encourage healthy growth.

It’s important to note that purple shamrock plants actively grow and flower during the fall to spring and go dormant in the summer. This might not happen every year, especially for houseplants, but it’s a possibility that requires some different care. When they are dormant, the foliage will degrade. If you see this occur, reduce watering and stop feeding your plant. As soon as you see new foliage begin to grow, resume your plant’s normal care routine.

Light

This plant grows well in full sun to partial shade, meaning roughly four hours of direct sunlight on most days. If you’re growing it outdoors and live in a hot climate, give it some protection from the hot afternoon sun. Indoors, the plant should be grown by a window that receives bright light. Regularly rotate the pot, so all sides of the plant end up facing the light and growing evenly. Too little light can cause the plant to become weak and leggy. 

Soil

The purple shamrock can grow in a variety of soil types as long as it has good drainage. Its roots are prone to rotting if the soil retains too much moisture. A loamy or sandy soil is best. And for container growth, a general, well-draining potting mix should be fine.

Water

Water to maintain an even amount of soil moisture on young purple shamrock plants. Established plants have some drought tolerance and are forgiving if you forget to water. During the growing season for purple shamrock plants, water whenever the top inch of soil has dried out. When the plant is dormant in the summer, lightly water about every two to three weeks to prevent the soil from drying out completely. 

Temperature and Humidity

These plants like temperatures between 60 and 75 degrees Fahrenheit, which makes them especially suitable to grow indoors in average room temperatures. They can tolerate nighttime temperatures down to 50 degrees Fahrenheit. Aim to protect the plants from strong winds outdoors and drafts indoors, especially those from air conditioners and heaters, as they can damage the foliage. A moderate humidity level is ideal for purple shamrock plants.

Fertilizer

Use either a slow-release or liquid fertilizer on the purple shamrock plant during its growing season, following label instructions. Indoors, a liquid fertilizer for houseplants is ideal. Mixing some compost into the soil also can help to promote healthy growth.

Types of Shamrock

Besides the purple shamrock, there are several plants in the oxalis genus that use the common name of shamrock, including:

• Oxalis acetosella: Also known as the wood sorrel or shamrock, this plant has bright green, heart-shaped leaves that occur in groups of three.
• Oxalis tetraphylla: This plant is commonly known as four-leaved sorrel or lucky clover because of its four split leaves. The leaves are bright green with a maroon center. 
• Oxalis lasiandra: This species is referred to as the Mexican shamrock or palm tree oxalis. It grows a little over a foot tall and bears bright pink flowers to crimson flowers.
• Oxalis adenophylla: This species is commonly known as the Chilean oxalis or silver shamrock. It features silvery green leaves and bears pink flowers with deep purple centers.
• Oxalis bowiei: The common names for this species include the Cape shamrock, Bowie’s wood sorrel, and red flower wood sorrel. It bears rose-colored to reddish-purple blooms.

Propagating Purple Shamrock

Mature purple shamrocks can be propagated by division during their growing season. Division is a cost-effective way to get new plants, and it prevents the mature plant from becoming overcrowded. Here's how:

1. Carefully dig up the plant, keeping the roots as intact as possible.
2. Gently pull apart the root ball to divide it in half (or into more sections if your plant is very large). Try to do this by hand to avoid tearing the roots, though you can use sterile garden scissors on very tangled roots. 
3. Replant each new section either in the ground or in a container that's just slightly larger than its root ball. Water the plants.

How to Grow Purple Shamrock From Seed

Purple shamrocks are grown from bulbs, rather than seeds. The best time to plant is in the spring. Plant the bulbs with the narrower end facing up roughly 1 to 2 inches down in the soil. Space multiple bulbs approximately 3 to 4 inches apart. Water the soil after planting, and make sure it does not remain waterlogged. Continue to water whenever the top 1 to 2 inches of soil dries out. Make sure the bulbs are in a warm, bright spot (either in a container or in the ground). You should see growth in three to four weeks. 

Potting and Repotting Purple Shamrock

Select a pot that’s just slightly larger than your purple shamrock’s root ball. Make sure it has ample drainage holes. An unglazed clay container is ideal because it will allow excess soil moisture to escape through its walls. Use a quality all-purpose potting mix that drains well. 

Plan to repot every two years in just one container size up. Gently loosen the plant from its old container, and shake off loose soil. Then, replant it at the same depth in its new container with fresh potting mix. Finally, water the plant. 

Overwintering

When grown outside of their hardiness zones, purple shamrocks must be kept indoors for the winter. Bring them inside well before any frost is in the forecast and while the nights are still above 50 degrees Fahrenheit. Place the plant by your brightest window, ideally one that faces south. And make sure it's not in the line of any drafts. Aim to keep the room temperature below 80 degrees Fahrenheit; anything warmer can trick your plant into thinking it's summertime and cause it to go dormant. Continue to water as you did when the plant was outdoors.

Common Pests & Plant Diseases

Purple shamrocks are prone to a few common pests and diseases. Some pests include mealybugs, aphids, and spider mites. Houseplants are more prone to pest issues, as wind and rainfall outside often knock pests off plants. Treat infestations with an insecticidal soap. 

A common disease of purple shamrocks is powdery mildew, a fungal disease that creates white spots on the foliage. This often is a result of humid conditions and poor air flow. Avoid overhead watering, and don’t crowd your plants.

How to Get Purple Shamrock to Bloom

Purple shamrocks bloom from fall to spring with small, five-petal flowers that grow in clusters above the foliage. Just like the leaves, the blooms close at night and on cloudy days. Deadheading (removing spent blooms) is not necessary to promote blooming, but it will make for a tidier-looking plant. What does encourage blooming is providing your plant with enough sunlight, moisture, and fertilizer. Plants that are struggling with deficiencies will likely not bloom profusely or even at all. But a healthy shamrock grown in the conditions it likes will readily rebloom year after year.

Common Problems With Purple Shamrock

Purple shamrock plants are generally easy to maintain if you give them the proper growing conditions. But some common problems arise due to environmental issues.

Drooping Leaves

Drooping leaves are often due to insufficient water or light (or both). However, this also might be a sign of the plant’s natural dormancy period if the temperature is rising. If your plant should not be going dormant, try giving it a little more light to see whether that perks up the foliage. Also, make sure you’re not letting the soil dry out.

Leaves Turning Brown

Leaves turning brown or just not looking as vibrant as usual can also be a sign that your purple shamrock is heading into dormancy. Allow your plant to go through this natural process, and cut back on watering and feeding. Resume your normal watering and feeding once you see new growth starting. At that point, you can trim off any degraded foliage.