Cold hardiness & minimum temperature

Is Hemianthus micranthemoides (Hemianthus micranthemoides)cold hardy? Hardiness zone & min temp

Also called pearl weed, pearlwort.

More about hemianthus micranthemoides

About Hemianthus micranthemoides

Hemianthus micranthemoides · also called pearl weed, pearlwort · tropical

Hemianthus micranthemoides, pearl weed, is a versatile small-leaved stem plant for freshwater aquascapes. Slender stems carry whorls of tiny bright-green leaves and can be grown tall as a bushy midground, trimmed low as a carpet, or left to trail. It is far easier than dwarf baby tears, growing well in moderate light and pearling vigorously when CO2 is supplied.

Cold limit: USDA Not applicable (tropical aquarium plant, indoor) · RHS H1b (20-28°C)

What hemianthus micranthemoides's hardiness rating actually means

Hemianthus micranthemoides 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 Not applicable (tropical aquarium plant, indoor) — 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). Hemianthus micranthemoides has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for hemianthus micranthemoides 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 hemianthus micranthemoides 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 hemianthus micranthemoides can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Hemianthus micranthemoides hardiness — frequently asked questions

Is hemianthus micranthemoides cold hardy?

Hemianthus micranthemoides 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. Hemianthus micranthemoides can only live outside year-round in genuinely frost-free climates (roughly USDA Not applicable (tropical aquarium plant, indoor)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature hemianthus micranthemoides can survive?

What hardiness zone is hemianthus micranthemoides?

Hemianthus micranthemoides is rated USDA Not applicable (tropical aquarium plant, indoor) and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can hemianthus micranthemoides 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 hemianthus micranthemoides 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.