Cold hardiness & minimum temperature

Is Formosanum Toad Lily (Tricyrtis formosana)cold hardy? Hardiness zone & min temp

Also called Formosa toad lily, autumn toad lily.

More about formosanum toad lily

About Formosanum Toad Lily

Tricyrtis formosana · also called Formosa toad lily, autumn toad lily · flowering

Tricyrtis formosana is a shade-loving woodland perennial from Taiwan grown for its exotic late-summer-to-autumn flowers — small upright stars speckled in purple, mauve and white that resemble tiny orchids. Arching leafy stems spread gently by stolons to form colonies. It blooms when most of the shade garden has finished, lighting up dim corners.

Cold limit: USDA 4-9 (hardy garden perennial) · RHS H5 (-20 to 24°C)

What formosanum toad lily's hardiness rating actually means

Yes — formosanum toad lily is genuinely cold hardy. Rated RHS H5 and USDA 4-9 (hardy garden perennial), it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 4-9 (hardy garden perennial) — 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 −15 to −10 °C. Formosanum Toad Lily is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for formosanum toad lily as it gets too cold:

It tolerates winter lows to about −15 to −10 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can formosanum toad lily go outside or overwinter — and where?

Plant it out within USDA 4-9 (hardy garden perennial) and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 formosanum toad lily can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Formosanum Toad Lily hardiness — frequently asked questions

Is formosanum toad lily cold hardy?

Yes — formosanum toad lily is genuinely cold hardy. Rated RHS H5 and USDA 4-9 (hardy garden perennial), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Formosanum Toad Lily is hardy across USDA 4-9 (hardy garden perennial); it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature formosanum toad lily can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Formosanum Toad Lily is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is formosanum toad lily?

Formosanum Toad Lily is rated USDA 4-9 (hardy garden perennial) and RHS H5 — Hardy in most of the UK and in cold winters.

Can formosanum toad lily survive winter outside?

Plant it out within USDA 4-9 (hardy garden perennial) and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to formosanum toad lily below its minimum temperature?

It tolerates winter lows to about −15 to −10 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.