PL. —Oxalis triangularisBotanical illustration — drop image

Oxalis triangularis

Purple Shamrock

SpringSummerFallInvasive

8a–11bHardiness zone

Peak bloom windowZone 6b · frost-offset weeks

Winter

Not in bloom

Spring

Peak bloom

Summer

Peak bloom

Fall

Not in bloom

Peak bloom

In bloom

Peak bloom windowZone 6b · frost-offset weeks

Winter

Not in bloom

Spring

Peak bloom

Summer

Peak bloom

Fall

Not in bloom

Peak bloom

In bloom

Background

Oxalis triangularis, purple shamrock or false shamrock, is a small clump-forming plant grown from scaly bulbs, prized for its striking deep purple, butterfly-shaped leaflets held in threes on wiry stems — a color so saturated it reads almost black in low light. Pale pink to white funnel-shaped flowers rise just above the foliage on and off through the growing season, though most gardeners grow it for the leaves alone. The foliage shows a distinct daily rhythm called nyctinasty: leaflets fold closed at night or in low light and reopen fully in bright daylight, a movement quick enough to notice within an hour of a light change — normal behavior, not a sign of stress.

Native to Brazil, it is hardy outdoors only in mild, frost-free climates; everywhere else it is grown as a container plant or houseplant, brought in before frost or kept indoors year-round in a bright window. It is genuinely low-maintenance once its habits are understood: it goes through natural dormancy periods, sometimes more than once a year, during which the foliage yellows and dies back completely — cut it back, withhold most water, and it reliably regrows from the bulbs within a few weeks to a couple of months. Like other Oxalis species it contains oxalic acid throughout the plant, which makes it mildly toxic if eaten in quantity by cats, dogs, and grazing animals, and it can self-seed or spread by small offset bulbs into a naturalized patch in the mild climates where it's hardy outdoors.

Good companions

Hosta Sieboldiana Begonia 'Little Brother Montgomery'

Care guide

SunBright indirect light to part shade; direct hot sun bleaches and scorches the foliage

WaterModerate; allow the top inch of soil to dry between waterings

SoilWell-draining, average fertility

Spacing6–12 in

Height8–12 in

Zone8a – 11b

WinterIn zones colder than 8a, grow in a container and bring indoors before first frost, or lift the small bulbs and store dry and cool over winter; it also thrives as a year-round houseplant in a bright spot.

Invasive

Seasonal tasks

spring

watchIn zones colder than 8a, bring containers indoors or lift and store bulbs before the first fall frost

sowPlant small bulbs 1–2 in deep in spring, in a container or a part-shade garden bed once frost has passed

cutDivide congested clumps of bulbs every 2–3 years in spring as new growth resumes

summer

watchExpect the leaves to fold shut at night or in low light and reopen in bright daylight — this is normal daily movement, not distress

watchIf foliage yellows and collapses, let the plant go fully dormant: cut back the dead growth and withhold most water until new leaves emerge, often within a few weeks to two months

Common problems

Root rot

Symptoms

Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.

Treatment

Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.

Fungal leaf spot

Symptoms

Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.

Treatment

Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.