Cold hardiness & minimum temperature

Is Rusty Foxglove (Digitalis ferruginea)cold hardy? Hardiness zone & min temp

Also called rusty foxglove, rusty-hued foxglove.

More about rusty foxglove

About Rusty Foxglove

Digitalis ferruginea · also called rusty foxglove, rusty-hued foxglove · flowering

Rusty foxglove is an architectural perennial throwing slender, towering spires packed with small coppery, rust-veined bells in summer above a tidy evergreen rosette. Tougher and more sun- and drought-tolerant than the common foxglove, it suits gravel and naturalistic plantings. Often short-lived but self-seeding, and like all foxgloves it is toxic, carrying cardiac glycosides.

Cold limit: USDA 4-9 (hardy short-lived perennial) · RHS H5 (-23 to 29°C)

Watch for — Crown rot in wet, heavy soil: Winter wet rots the evergreen rosette. Plant on free-draining ground, add grit on clay, and avoid mulching directly over the crown.

What rusty foxglove's hardiness rating actually means

Yes — rusty foxglove is genuinely cold hardy. Rated RHS H5 and USDA 4-9 (hardy short-lived perennial), 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 4-9 (hardy short-lived perennial) — 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. Rusty Foxglove is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for rusty foxglove 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 rusty foxglove go outside or overwinter — and where?

Plant it out within USDA 4-9 (hardy short-lived perennial) 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 rusty foxglove can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Rusty Foxglove hardiness — frequently asked questions

Is rusty foxglove cold hardy?

Yes — rusty foxglove is genuinely cold hardy. Rated RHS H5 and USDA 4-9 (hardy short-lived perennial), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Rusty Foxglove is hardy across USDA 4-9 (hardy short-lived perennial); 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 rusty foxglove can survive?

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

What hardiness zone is rusty foxglove?

Rusty Foxglove is rated USDA 4-9 (hardy short-lived perennial) and RHS H5 — Hardy in most of the UK and in cold winters.

Can rusty foxglove survive winter outside?

Plant it out within USDA 4-9 (hardy short-lived perennial) 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 rusty foxglove 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.