Cold hardiness & minimum temperature

Is Pogostemon helferi (Pogostemon helferi)cold hardy? Hardiness zone & min temp

Also called downoi, little star plant.

More about pogostemon helferi

About Pogostemon helferi

Pogostemon helferi · also called downoi, little star plant · tropical

Downoi is a small, distinctive aquarium foreground plant from Thailand with wavy, crinkled green leaves arranged in a low star-shaped rosette. Grown submerged it stays compact and carpets slowly when its offsets are spread out. It is moderately demanding, rewarding bright light, CO2 and rich substrate with tight, characterful rosettes.

Cold limit: USDA 10-11 (tropical aquatic; grown indoors in aquaria) (22-28°C)

What pogostemon helferi's hardiness rating actually means

Pogostemon helferi 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 (tropical aquatic; grown indoors in aquaria) — 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). Pogostemon helferi has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for pogostemon helferi 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 pogostemon helferi 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 pogostemon helferi can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Pogostemon helferi hardiness — frequently asked questions

Is pogostemon helferi cold hardy?

Pogostemon helferi 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. Pogostemon helferi can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (tropical aquatic; grown indoors in aquaria)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature pogostemon helferi can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Pogostemon helferi has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is pogostemon helferi?

Pogostemon helferi is rated USDA 10-11 (tropical aquatic; grown indoors in aquaria) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can pogostemon helferi 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 pogostemon helferi 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.