Cold hardiness & minimum temperature

Is Flame nasturtium (Tropaeolum speciosum)cold hardy? Hardiness zone & min temp

Also called Flame nasturtium, Flame creeper, Scottish flame flower.

More about flame nasturtium

About Flame nasturtium

Tropaeolum speciosum · also called Flame nasturtium, Flame creeper · flowering

Flame nasturtium is a tuberous, herbaceous perennial climber native to the cool forests of Chile. Its brilliant scarlet flowers appear from midsummer to early autumn, followed by striking blue berries held in red calyces. It thrives in cool, moist gardens with its roots in shade and stems climbing into sun — a favourite for draping over dark evergreen hedges. RHS Award of Garden Merit holder.

Cold limit: USDA 8–10 · RHS H5 (-12 to 20°C)

Watch for — Failure to establish or return after winter: Most common in alkaline, dry, or south-facing warm soils; the tuber desiccates in summer heat — cool, acid, humus-rich soil with the root zone in shade is non-negotiable.

What flame nasturtium's hardiness rating actually means

Yes — flame nasturtium is genuinely cold hardy. Rated RHS H5 and USDA 8–10, 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 8–10 — 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. Flame nasturtium is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for flame nasturtium 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 flame nasturtium go outside or overwinter — and where?

Plant it out within USDA 8–10 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 flame nasturtium can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Flame nasturtium hardiness — frequently asked questions

Is flame nasturtium cold hardy?

Yes — flame nasturtium is genuinely cold hardy. Rated RHS H5 and USDA 8–10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Flame nasturtium is hardy across USDA 8–10; 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 flame nasturtium can survive?

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

What hardiness zone is flame nasturtium?

Flame nasturtium is rated USDA 8–10 and RHS H5 — Hardy in most of the UK and in cold winters.

Can flame nasturtium survive winter outside?

Plant it out within USDA 8–10 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 flame nasturtium 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.