Cold hardiness & minimum temperature

Is Janke's Gesneriad (Jancaea heldreichii)cold hardy? Hardiness zone & min temp

Also called Janke's Gesneriad, Olympus Gesneriad, Jankaea.

More about janke's gesneriad

About Janke's Gesneriad

Jancaea heldreichii · also called Janke's Gesneriad, Olympus Gesneriad · flowering

Jancaea heldreichii is a monotypic, critically range-restricted gesneriad endemic to the limestone cliffs of Mount Olympus in Greece, growing in damp shaded rock crevices at 700–1,400 m elevation. In cultivation it demands an alpine house or cold greenhouse, perfect drainage, shade, and consistent cool temperatures — it is considered one of the most challenging alpine gesneriads to grow. The most important care fact is that the silver-haired rosette will rot instantly if water settles on the leaves, so overhead watering must be avoided at all times. It is not ASPCA-listed; use caution with pets.

Cold limit: USDA 6-8 · RHS H5 (-10–18°C)

What janke's gesneriad's hardiness rating actually means

Yes — janke's gesneriad is genuinely cold hardy. Rated RHS H5 and USDA 6-8, 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 6-8 — 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. Janke's Gesneriad is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for janke's gesneriad 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 janke's gesneriad go outside or overwinter — and where?

Plant it out within USDA 6-8 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 janke's gesneriad can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Janke's Gesneriad hardiness — frequently asked questions

Is janke's gesneriad cold hardy?

Yes — janke's gesneriad is genuinely cold hardy. Rated RHS H5 and USDA 6-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Janke's Gesneriad is hardy across USDA 6-8; 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 janke's gesneriad can survive?

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

What hardiness zone is janke's gesneriad?

Janke's Gesneriad is rated USDA 6-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can janke's gesneriad survive winter outside?

Plant it out within USDA 6-8 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 janke's gesneriad 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.