Cold hardiness & minimum temperature
Is Summer Wave Amethyst Wishbone Flower (Torenia fournieri)cold hardy? Hardiness zone & min temp
Also called Wishbone Flower, Bluewings, Clown Flower.
More about summer wave amethyst wishbone flower
About Summer Wave Amethyst Wishbone Flower
Torenia fournieri · also called Wishbone Flower, Bluewings · flowering
Wishbone Flower is a heat-tolerant annual that thrives in shade with tubular two-toned blooms in amethyst purple and white. A superb choice for hanging baskets and shaded beds, it flowers all summer without deadheading. The ASPCA lists Torenia as non-toxic to dogs and cats, making it a pet-safe choice for the garden.
Cold limit: USDA 10-11 (grown as a summer annual elsewhere) · RHS H1c (18-30°C)
What summer wave amethyst wishbone flower's hardiness rating actually means
Summer Wave Amethyst Wishbone Flower is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 10-11 (grown as a summer annual elsewhere) — 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 °C (and never frost). Summer Wave Amethyst Wishbone Flower has no frost tolerance at all — it is an indoor plant in any climate with a real winter.
Concretely, for summer wave amethyst wishbone flower as it gets too cold:
- Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
- A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
- Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.
Can summer wave amethyst wishbone flower go outside or overwinter — and where?
- It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually.
- Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
- It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.
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 summer wave amethyst wishbone flower can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.
Summer Wave Amethyst Wishbone Flower hardiness — frequently asked questions
Is summer wave amethyst wishbone flower cold hardy?
Summer Wave Amethyst Wishbone Flower is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Summer Wave Amethyst Wishbone Flower can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (grown as a summer annual elsewhere)); everywhere else it is a houseplant that summers out at most.
What is the minimum temperature summer wave amethyst wishbone flower can survive?
Minimum survivable temperature is roughly about 5 °C (and never frost). Summer Wave Amethyst Wishbone Flower has no frost tolerance at all — it is an indoor plant in any climate with a real winter.
What hardiness zone is summer wave amethyst wishbone flower?
Summer Wave Amethyst Wishbone Flower is rated USDA 10-11 (grown as a summer annual elsewhere) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.
Can summer wave amethyst wishbone flower survive winter outside?
It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.
What happens to summer wave amethyst wishbone flower below its minimum temperature?
Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.
Keep reading
- Summer Wave Amethyst Wishbone Flower care — the full brief (light, water, soil, problems, pet safety)
- USDA hardiness zones — find yours and what grows there
- Is summer wave amethyst wishbone flower hardy in the UK? — the RHS-rating version
- RHS hardiness ratings — the UK system explained
- Frost-date calculator — your real outdoor window
- The USDA hardiness zone map, explained
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- All 11687plant hardiness & min-temp guides