Cold hardiness & minimum temperature

Is Cycas Rumphii (Cycas rumphii)cold hardy? Hardiness zone & min temp

Also called queen sago, Rumpf's cycad, Moluccan cycad.

More about cycas rumphii

About Cycas Rumphii

Cycas rumphii · also called queen sago, Rumpf's cycad · tropical

Cycas rumphii, the queen sago, is a tall tropical cycad from the Malay Archipelago bearing a single stout trunk crowned with long, glossy, feather-like fronds. Strictly frost-tender, it suits warm coastal and glasshouse cultivation. Like all cycads it is extremely slow and, critically, severely poisonous to pets and people if eaten.

Cold limit: USDA 10-11 (frost-free only; indoor/glasshouse in most US/UK) · RHS H1b (18-30C; frost-tender, protect below 5C)

Watch for — Frost damage: No frost tolerance; even light freezes kill the foliage and can be fatal, so keep frost-free.

What cycas rumphii's hardiness rating actually means

Cycas Rumphii 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 H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA 10-11 (frost-free only; indoor/glasshouse in most US/UK) — 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 10 °C (sustained cold below this is damaging). Cycas Rumphii has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for cycas rumphii as it gets too cold:

Below about about 10 °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 cycas rumphii go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 10 °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 cycas rumphii can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Cycas Rumphii hardiness — frequently asked questions

Is cycas rumphii cold hardy?

Cycas Rumphii 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. Cycas Rumphii can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (frost-free only; indoor/glasshouse in most US/UK)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature cycas rumphii can survive?

What hardiness zone is cycas rumphii?

Cycas Rumphii is rated USDA 10-11 (frost-free only; indoor/glasshouse in most US/UK) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can cycas rumphii survive winter outside?

It can holiday outdoors in summer once nights are reliably above 10 °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 cycas rumphii below its minimum temperature?

Below about about 10 °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.