Cold hardiness & minimum temperature

Is Hound's-tongue (Cynoglossum officinale)cold hardy? Hardiness zone & min temp

Also called Hound's-tongue, Gypsy Flower, Dog's Tongue, Common Hound's-tongue.

More about hound's-tongue

About Hound's-tongue

Cynoglossum officinale · also called Hound's-tongue, Gypsy Flower · flowering

Hound's-tongue is a biennial or short-lived perennial native to Europe and temperate Asia, widely naturalised in North America. It thrives in dry, disturbed ground, roadsides, and chalk grassland in full sun with free-draining, low-fertility soil. The most important care fact for cultivated settings is to avoid over-watering and rich soil, which cause lax, floppy growth. This plant is toxic to pets and livestock due to pyrrolizidine alkaloid content.

Cold limit: USDA 4-8 · RHS H7 (-20 to 25°C)

Watch for — Crown rot: Standing water or heavy clay soil rots the basal rosette over winter; ensure sharp drainage and avoid mulching close to the crown.

What hound's-tongue's hardiness rating actually means

Yes — hound's-tongue is genuinely cold hardy. Rated RHS H7 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 4-8 — 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 below about −20 °C. Hound's-tongue is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for hound's-tongue as it gets too cold:

It tolerates winter lows to about −20 °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 hound's-tongue go outside or overwinter — and where?

Plant it out within USDA 4-8 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 hound's-tongue can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Hound's-tongue hardiness — frequently asked questions

Is hound's-tongue cold hardy?

Yes — hound's-tongue is genuinely cold hardy. Rated RHS H7 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Hound's-tongue is hardy across USDA 4-8; 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 hound's-tongue can survive?

Minimum survivable temperature is roughly below about −20 °C. Hound's-tongue is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is hound's-tongue?

Hound's-tongue is rated USDA 4-8 and RHS H7 — Hardy in the severest European continental winters.

Can hound's-tongue survive winter outside?

Plant it out within USDA 4-8 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 hound's-tongue below its minimum temperature?

It tolerates winter lows to about −20 °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.