Cold hardiness & minimum temperature

Is Lobelia cardinalis (Lobelia cardinalis)cold hardy? Hardiness zone & min temp

Also called Cardinal Flower, Red Lobelia.

More about lobelia cardinalis

About Lobelia cardinalis

Lobelia cardinalis · also called Cardinal Flower, Red Lobelia · flowering

Lobelia cardinalis is a striking moisture-loving perennial bearing tall spikes of vivid scarlet, tubular flowers above upright leafy stems in mid to late summer. Native to streamsides and wet meadows, it is a celebrated hummingbird and pollinator plant for pond margins, rain gardens and consistently damp borders.

Cold limit: USDA 3-9 (hardy perennial, often short-lived) · RHS H5 (-25 to 30°C)

Watch for — Winter crown rot: Basal rosettes can rot if buried under wet mulch or waterlogged frozen soil. Keep the crown clear of heavy debris over winter.

What lobelia cardinalis's hardiness rating actually means

Yes — lobelia cardinalis is genuinely cold hardy. Rated RHS H5 and USDA 3-9 (hardy perennial, often short-lived), 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 3-9 (hardy perennial, often short-lived) — 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. Lobelia cardinalis is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for lobelia cardinalis 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 lobelia cardinalis go outside or overwinter — and where?

Plant it out within USDA 3-9 (hardy perennial, often short-lived) 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 lobelia cardinalis can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Lobelia cardinalis hardiness — frequently asked questions

Is lobelia cardinalis cold hardy?

Yes — lobelia cardinalis is genuinely cold hardy. Rated RHS H5 and USDA 3-9 (hardy perennial, often short-lived), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Lobelia cardinalis is hardy across USDA 3-9 (hardy perennial, often short-lived); 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 lobelia cardinalis can survive?

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

What hardiness zone is lobelia cardinalis?

Lobelia cardinalis is rated USDA 3-9 (hardy perennial, often short-lived) and RHS H5 — Hardy in most of the UK and in cold winters.

Can lobelia cardinalis survive winter outside?

Plant it out within USDA 3-9 (hardy perennial, often short-lived) 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 lobelia cardinalis 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.