Cold hardiness & minimum temperature

Is Mexican Butterwort (Pinguicula moranensis)cold hardy? Hardiness zone & min temp

Also called Mexican butterwort, Butterwort.

More about mexican butterwort

About Mexican Butterwort

Pinguicula moranensis · also called Mexican butterwort, Butterwort · houseplant

Pinguicula moranensis is the most widely cultivated Mexican butterwort, native to highland forests and cliffs across Mexico and Guatemala at elevations of 1,800-3,400 m. It is a heterophyllous species that produces large, flat, sticky carnivorous leaves in summer that trap fungus gnats and other small insects, then switches to compact succulent rosettes in winter — the critical care point is to withhold water almost completely during the winter succulent phase. It is not confirmed as non-toxic on the ASPCA database and carries a precautionary mildly-toxic rating.

Cold limit: USDA 9-11 (indoor in most climates) · RHS H2 (5-29°C)

Watch for — Rotting in winter: Continuing tray watering after the plant switches to its succulent rosette is the leading cause of root and crown rot. Transition to very infrequent light misting as soon as the compact winter form appears, typically in late autumn.

What mexican butterwort's hardiness rating actually means

Mexican Butterwort is half-hardy (RHS H2). 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 H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 9-11 (indoor in most climates) — 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 1 to 5 °C — tolerates cold but no real frost. Mexican Butterwort shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for mexican butterwort as it gets too cold:

Down to roughly about 1 to 5 °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 mexican butterwort go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor in most climates) 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 mexican butterwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline mexican butterwort

Mexican Butterwort 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.

Mexican Butterwort hardiness — frequently asked questions

Is mexican butterwort cold hardy?

Mexican Butterwort is half-hardy (RHS H2). 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 9-11 (indoor in most climates) (and sheltered UK gardens) mexican butterwort can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature mexican butterwort can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Mexican Butterwort shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is mexican butterwort?

Mexican Butterwort is rated USDA 9-11 (indoor in most climates) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can mexican butterwort survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9-11 (indoor in most climates) 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 mexican butterwort 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.