Cold hardiness & minimum temperature

Is Utricularia subulata (Utricularia subulata)cold hardy? Hardiness zone & min temp

Also called Awl-shaped Bladderwort, Zigzag Bladderwort.

More about utricularia subulata

About Utricularia subulata

Utricularia subulata · also called Awl-shaped Bladderwort, Zigzag Bladderwort · flowering

The Awl-shaped Bladderwort is a tiny terrestrial carnivorous plant with a near-cosmopolitan warm-temperate to tropical range. Almost leafless above ground, it traps microscopic prey in minute underground bladders and sends up wiry, zigzag stems of small yellow flowers. It thrives in permanently wet, peaty, nutrient-poor soil with bright light, often appearing as a welcome weed in bog pots.

Cold limit: USDA 8-11 (warm-temperate to tropical; protect from sustained frost) · RHS H2 (15-30°C; protect from hard frost)

What utricularia subulata's hardiness rating actually means

Utricularia subulata 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 8-11 (warm-temperate to tropical; protect from sustained frost) — 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. Utricularia subulata shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for utricularia subulata 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 utricularia subulata go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 (warm-temperate to tropical; protect from sustained frost) 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 utricularia subulata 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 utricularia subulata

Utricularia subulata 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.

Utricularia subulata hardiness — frequently asked questions

Is utricularia subulata cold hardy?

Utricularia subulata 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 8-11 (warm-temperate to tropical; protect from sustained frost) (and sheltered UK gardens) utricularia subulata can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature utricularia subulata can survive?

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

What hardiness zone is utricularia subulata?

Utricularia subulata is rated USDA 8-11 (warm-temperate to tropical; protect from sustained frost) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can utricularia subulata survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 (warm-temperate to tropical; protect from sustained frost) 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 utricularia subulata 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.