Cold hardiness & minimum temperature

Is Phoenix Moss (Fissidens fontanus)cold hardy? Hardiness zone & min temp

Also called Water Pocket Moss, Fountain Feather Moss.

More about phoenix moss

About Phoenix Moss

Fissidens fontanus · also called Water Pocket Moss, Fountain Feather Moss · tropical

Fissidens fontanus is an elegant aquatic moss forming feathery, bright-green fronds that drape beautifully over rocks and driftwood. Native to North America, it is one of the most popular aquascape mosses for cool to warm tanks. Pet-safe; true mosses carry no documented toxicity to cats, dogs, or aquarium fish.

Cold limit: USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics) · RHS H4 (15–24°C)

Watch for — Slow growth in warm tanks: This moss prefers cooler water; in tanks above 26°C growth slows noticeably. Keep temperature in the lower end of its range for best results.

What phoenix moss's hardiness rating actually means

Yes — phoenix moss is genuinely cold hardy. Rated RHS H4 and USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics), it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics) — 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 to −5 °C. Phoenix Moss is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for phoenix moss as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 phoenix moss go outside or overwinter — and where?

Plant it out within USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics) 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 phoenix moss can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Phoenix Moss hardiness — frequently asked questions

Is phoenix moss cold hardy?

Yes — phoenix moss is genuinely cold hardy. Rated RHS H4 and USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Phoenix Moss is hardy across USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics); 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 phoenix moss can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Phoenix Moss is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is phoenix moss?

Phoenix Moss is rated USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics) and RHS H4 — Hardy in an average winter across much of the temperate world.

Can phoenix moss survive winter outside?

Plant it out within USDA 6–10 (native cool-water streams in North America; tolerates cooler conditions than most tropical aquatics) 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 phoenix moss below its minimum temperature?

It tolerates winter lows to about −10 to −5 °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.