How to grow and care for a shamrock plant

What you need to know about shamrock

Name: shamrock, sorrel, oxalis, Oxalis species.

Height: 15cm tall and up to 20cm in spread.

Foliage: soft, three-lobed leaves; most are green, but some are purple or have coloured central markings.

Climate: temperate to cool temperate.

Soil: well-drained to gravelly loam.

Position: sunny open spot; tolerates light shade but flowers best in full sun.

Flowering: small five-petalled flowers in a variety of colours and combinations, some striped and others with coloured “eyes”.

Feeding: use long-term controlled-release and liquid fertilisers.

Watering: keep moist but not wet; withhold water when bulbs are dormant.

Appearance and characteristics of the shamrock plant

Oxalis, sorrels or shamrocks are ground-hugging plants that grow from bulbs. They usually grow to no more than about 15cm high, although some of the weedy species can be taller. Their leaves are three-lobed, like clover. Although they are mainly green, some types have white, red or brown markings on each lobe, and others are fully coloured, like the purple leaf shamrock pictured. Each leaf is carried on a slender stem arising from the bulb.

Flowers have five petals and range in colour from white through to pinks, mauves and crimson, orange and yellow. They are produced in clusters atop slender stalks. Shamrock bulbs are small and brown, with some also producing a deep, fleshy root.

Weed potential

The more invasive and therefore weedy types of oxalis produce masses of bulbils (tiny bulbs) around the main bulb, which tend to fall off when you try to dig the plants out, spreading through the soil. That’s why it’s so difficult to control oxalis.

The invasive tendencies of soursob (Oxalis pes-caprae), creeping oxalis (O. corniculata) and pink sorrel (O. corymbosa) have seen oxalis in general classified as a weed, but there are many non-invasive species and varieties that make attractive garden or potted plants.

If you do have any of the three weedy oxalis in your garden, try to eradicate them wherever possible. Soursob, pink sorrel or creeping oxalis in garden beds can be dug out or easily treated with a non-selective herbicide, boiling water or a salt solution to kill them. Creeping oxalis in a lawn is a little more complicated. You can try to dig it out, finding the main crown of each plant, but most likely you will need to use a selective broadleaf lawn weeder product.

How to plant and grow a shamrock plant

Many of the ornamental varieties of shamrock thrive in rock or alpine landscapes, where they can be confined, and their flowers fully appreciated.

It’s unlikely you will be able to buy shamrock bulbs, but plants of the best forms will be available from specialist rare plant nurseries. Do check plant labels before buying to ensure you’re not buying one with weed potential!

Growing shamrock in the garden

• Shamrock will grow and flower best in full sun, although it will tolerate light shade from overhanging branches. Dense shade will inhibit flowers, so is best avoided.
• Prepare planting sites by forking over the soil and adding a long-term controlled-release fertiliser for flowering plants.
• Position plants so the crown of the main bulb is just at soil level and the leaf stems emerging from it are well clear of the soil.

Growing shamrock in pots

• If you are concerned about plants spreading through your garden, then grow your shamrock plant in a pot. A 180mm diameter pot will hold several plants—they don’t mind being tightly packed. Use a premium-quality terracotta and tub potting mix that drains freely but holds enough moisture to keep plants healthy.
• Pots are best placed outside where they will receive plenty of light and sun, but they can be taken indoors when plants are in flower.

Climate

In warm areas, shamrock will remain in leaf all year round, but in cooler climates where there is a marked winter season, plants may go into dormancy in late autumn. The leaves will yellow and fall off, but don’t discard the plants—the bulbs are still alive! Stop watering until you see the first sign of leaves in early spring, then resume watering again.

Watering your shamrock plant

Shamrock likes a moist but well-drained soil—the bulbs may rot if they are too wet. Test the soil or potting mix with your finger. If it feels dry, then water. Usually a weekly water from spring to autumn is sufficient.

Don’t water your shamrock plant in the garden or in pots over winter if it loses its leaves and becomes dormant. Move pots to a sheltered spot out of the weather.

Fertilising your shamrock plant

Apply a long-term controlled-release fertiliser for flowering plants at the start of spring each year, to plants in the garden as well as those in pots. Supplement this with a water-soluble or liquid fertiliser once a month over the main growing season: spring to early autumn.

Diseases and pests that affect shamrock plants

Shamrock is reasonably disease and pest free. The only trouble you may encounter is bulbs rotting if the soil is too wet.

If you like this then try

Peony: a cool-climate flowering plant with full rose-like blooms from white to deep crimson.

Cyclamen: a tuberous flowering plant with white to cerise flowers on tall stems above grey-green heart-shaped leaves.

Liriope: a grass-like plant with purple flowers, often grown as a border; an excellent foil to delicate shamrock flowers.

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