Cold hardiness & minimum temperature

Is White Hyssop (Hyssopus officinalis 'Albus')cold hardy? Hardiness zone & min temp

Also called White Hyssop, White-Flowered Hyssop.

More about white hyssop

About White Hyssop

Hyssopus officinalis 'Albus' · also called White Hyssop, White-Flowered Hyssop · herb

White Hyssop is a compact, semi-evergreen sub-shrub bearing dense whorled spikes of pure white flowers from midsummer through early autumn. Intensely aromatic, bitter-camphorous foliage. Strongly attractive to bees and butterflies. Excellent for herb knot gardens, low hedging, or cottage borders. Hardy, drought-tolerant once established, and thrives in alkaline, well-drained soils.

Cold limit: USDA 4–9 · RHS H7 (-15–30°C)

Watch for — Root rot in wet soil: Waterlogged winter soil quickly kills hyssop. Ensure sharply drained conditions; plant on slopes, raised beds, or in gravel gardens. In containers, use free-draining compost with added grit and never leave pots standing in water.

What white hyssop's hardiness rating actually means

Yes — white hyssop is genuinely cold hardy. Rated RHS H7 and USDA 4–9, 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 4–9 — 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 below about −20 °C. White Hyssop is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for white hyssop 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 white hyssop go outside or overwinter — and where?

Plant it out within USDA 4–9 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 white hyssop can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

White Hyssop hardiness — frequently asked questions

Is white hyssop cold hardy?

Yes — white hyssop is genuinely cold hardy. Rated RHS H7 and USDA 4–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. White Hyssop is hardy across USDA 4–9; 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 white hyssop can survive?

Minimum survivable temperature is roughly below about −20 °C. White Hyssop is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is white hyssop?

White Hyssop is rated USDA 4–9 and RHS H7 — Hardy in the severest European continental winters.

Can white hyssop survive winter outside?

Plant it out within USDA 4–9 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 white hyssop 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.