Cold hardiness & minimum temperature

Is Titanotrichum oldhamii (Titanotrichum oldhamii)cold hardy? Hardiness zone & min temp

Also called Oldham's titanotrichum, Taiwanese gesneriad.

More about titanotrichum oldhamii

About Titanotrichum oldhamii

Titanotrichum oldhamii · also called Oldham's titanotrichum, Taiwanese gesneriad · flowering

Titanotrichum oldhamii is an unusual woodland gesneriad from Taiwan, southern China, and Japan, prized by collectors for tall spikes of tubular yellow flowers with maroon throats. It spreads by underground stolons tipped with rice-like bulbils and dies back to rest in winter. Cool, shaded, humid, woodland conditions suit this hardy, shade-loving perennial best.

Cold limit: USDA 8-9 (root-hardy with mulch in mild, sheltered gardens) · RHS H3 (10-24°C)

Watch for — Foliage dying back: Normal winter dormancy rather than decline. Reduce watering and keep the rhizomes and bulbils cool and barely moist until spring growth resumes.

What titanotrichum oldhamii's hardiness rating actually means

Titanotrichum oldhamii is half-hardy (RHS H3). 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 H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 8-9 (root-hardy with mulch in mild, sheltered gardens) — 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 to 1 °C — a light, short frost only. Titanotrichum oldhamii shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for titanotrichum oldhamii as it gets too cold:

Down to roughly about −5 to 1 °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 titanotrichum oldhamii go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-9 (root-hardy with mulch in mild, sheltered gardens) 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 titanotrichum oldhamii can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline titanotrichum oldhamii

Titanotrichum oldhamii 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.

Titanotrichum oldhamii hardiness — frequently asked questions

Is titanotrichum oldhamii cold hardy?

Titanotrichum oldhamii is half-hardy (RHS H3). 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 8-9 (root-hardy with mulch in mild, sheltered gardens) (and sheltered UK gardens) titanotrichum oldhamii can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature titanotrichum oldhamii can survive?

Minimum survivable temperature is roughly about −5 to 1 °C — a light, short frost only. Titanotrichum oldhamii shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is titanotrichum oldhamii?

Titanotrichum oldhamii is rated USDA 8-9 (root-hardy with mulch in mild, sheltered gardens) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can titanotrichum oldhamii survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-9 (root-hardy with mulch in mild, sheltered gardens) 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 titanotrichum oldhamii 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.