Cold hardiness & minimum temperature

Is Good King Henry (Blitum bonus-henricus)cold hardy? Hardiness zone & min temp

Also called Good King Henry, Mercury, Wild Spinach.

More about good king henry

About Good King Henry

Blitum bonus-henricus · also called Good King Henry, Mercury · herb

Good King Henry is an old-fashioned hardy perennial vegetable in the goosefoot family, grown for spinach-like leaves and asparagus-like spring shoots. Tolerant and long-lived, it thrives in rich, moist soil and part shade, cropping for years from one planting. Leaves contain oxalic acid, so they are best lightly cooked rather than eaten raw in quantity.

Cold limit: USDA 3-9 · RHS H6 (10-24°C)

What good king henry's hardiness rating actually means

Yes — good king henry is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 3-9 — 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 −20 to −15 °C. Good King Henry is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for good king henry as it gets too cold:

It tolerates winter lows to about −20 to −15 °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 good king henry go outside or overwinter — and where?

Plant it out within USDA 3-9 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 good king henry can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Good King Henry hardiness — frequently asked questions

Is good king henry cold hardy?

Yes — good king henry is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Good King Henry is hardy across USDA 3-9; 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 good king henry can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Good King Henry is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is good king henry?

Good King Henry is rated USDA 3-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can good king henry survive winter outside?

Plant it out within USDA 3-9 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 good king henry below its minimum temperature?

It tolerates winter lows to about −20 to −15 °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.