Cold hardiness & minimum temperature

Is False shamrock (Oxalis triangularis)cold hardy? Hardiness zone & min temp

Also called purple shamrock, love plant, wood sorrel (purple).

About False shamrock

Oxalis triangularis · also called purple shamrock, love plant · flowering

False shamrock is a Brazilian tuberous perennial with deep purple triangular leaves that fold up at night, and small pink flowers. Easy and forgiving but mildly toxic to pets due to oxalic acid. Tubers cycle through dormancy.

Oxalis triangularis, a tuberous wood-sorrel native to Brazil, grown for its deep-purple triangular trifoliate leaves that arise from small scaly underground tubers.

Cyclical grower that dies back into tuber dormancy after heavy flowering or sustained heat above roughly 27C; ASPCA lists Oxalis as toxic to cats and dogs due to soluble calcium oxalates causing oral irritation and GI upset.

Cold limit: USDA 8-11 (indoor in most US homes) · RHS H3 (15-24°C)

Sources: libguides.nybg.org, aspca.org

What false shamrock's hardiness rating actually means

False shamrock is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 8-11 (indoor in most US homes) — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. False shamrock shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for false shamrock as it gets too cold:

Down to roughly about −5 to 1 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can false shamrock go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 (indoor in most US homes) or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when false shamrock can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline false shamrock

False shamrock is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

False shamrock hardiness — frequently asked questions

Is false shamrock cold hardy?

False shamrock is half-hardy (RHS H3). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 8-11 (indoor in most US homes) (and sheltered UK gardens) false shamrock can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature false shamrock can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. False shamrock shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is false shamrock?

False shamrock is rated USDA 8-11 (indoor in most US homes) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can false shamrock survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 (indoor in most US homes) or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect false shamrock from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.