Cold hardiness & minimum temperature

Is Olympic St. John's Wort (Hypericum olympicum)cold hardy? Hardiness zone & min temp

Also called Olympic St. John's Wort, Mount Olympus St. John's Wort.

More about olympic st. john's wort

About Olympic St. John's Wort

Hypericum olympicum · also called Olympic St. John's Wort, Mount Olympus St. John's Wort · flowering

A compact, drought-tolerant dwarf subshrub native to rocky limestone slopes on Mount Olympus and throughout the Balkans. Produces a spectacular summer display of large, bright yellow flowers up to 5 cm across from June to August. Exceptional for rock gardens, dry walls, gravel beds, and sunny alpine troughs.

Cold limit: USDA 5–9 · RHS H6 (-20 to 35°C)

Watch for — Root rot in wet winter soil: The most common failure in UK and Pacific Northwest gardens. Excellent drainage is essential year-round but especially in winter. Plant on a slope, in a raised bed, or in a container that can be moved under cover during prolonged wet, cold spells.

What olympic st. john's wort's hardiness rating actually means

Yes — olympic st. john's wort is genuinely cold hardy. Rated RHS H6 and USDA 5–9, 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 5–9 — 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. Olympic St. John's Wort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for olympic st. john's wort 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 olympic st. john's wort go outside or overwinter — and where?

Plant it out within USDA 5–9 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 olympic st. john's wort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Olympic St. John's Wort hardiness — frequently asked questions

Is olympic st. john's wort cold hardy?

Yes — olympic st. john's wort is genuinely cold hardy. Rated RHS H6 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Olympic St. John's Wort is hardy across USDA 5–9; 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 olympic st. john's wort can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Olympic St. John's Wort is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is olympic st. john's wort?

Olympic St. John's Wort is rated USDA 5–9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can olympic st. john's wort survive winter outside?

Plant it out within USDA 5–9 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 olympic st. john's wort 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.