Cold hardiness & minimum temperature

Is Pusillus Miniature Sweet Flag (Acorus gramineus 'Pusillus')cold hardy? Hardiness zone & min temp

Also called miniature sweet flag, dwarf acorus.

More about pusillus miniature sweet flag

About Pusillus Miniature Sweet Flag

Acorus gramineus 'Pusillus' · also called miniature sweet flag, dwarf acorus · houseplant

'Pusillus' is a dwarf Japanese sweet flag forming low, grassy tufts of fine deep-green blades just a few centimetres tall. A favourite for terrariums, fairy gardens, aquascaping foregrounds and miniature water features, it loves constant moisture and cool, bright conditions. Slow and compact, it makes a tidy living groundcover but resents drying out and prolonged total submersion.

Cold limit: USDA 6-11 (grown indoors or in terrariums in cooler regions) · RHS H5 (-5 to 26°C)

What pusillus miniature sweet flag's hardiness rating actually means

Yes — pusillus miniature sweet flag is genuinely cold hardy. Rated RHS H5 and USDA 6-11 (grown indoors or in terrariums in cooler regions), 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 6-11 (grown indoors or in terrariums in cooler regions) — 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. Pusillus Miniature Sweet Flag is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for pusillus miniature sweet flag 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 pusillus miniature sweet flag go outside or overwinter — and where?

Plant it out within USDA 6-11 (grown indoors or in terrariums in cooler regions) 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 pusillus miniature sweet flag can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Pusillus Miniature Sweet Flag hardiness — frequently asked questions

Is pusillus miniature sweet flag cold hardy?

Yes — pusillus miniature sweet flag is genuinely cold hardy. Rated RHS H5 and USDA 6-11 (grown indoors or in terrariums in cooler regions), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Pusillus Miniature Sweet Flag is hardy across USDA 6-11 (grown indoors or in terrariums in cooler regions); 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 pusillus miniature sweet flag can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Pusillus Miniature Sweet Flag is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is pusillus miniature sweet flag?

Pusillus Miniature Sweet Flag is rated USDA 6-11 (grown indoors or in terrariums in cooler regions) and RHS H5 — Hardy in most of the UK and in cold winters.

Can pusillus miniature sweet flag survive winter outside?

Plant it out within USDA 6-11 (grown indoors or in terrariums in cooler regions) 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 pusillus miniature sweet flag 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.