Cold hardiness & minimum temperature

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

Also called Golden St. John's Wort, Cedarglade St. Johnswort, Sunburst St. John's Wort.

More about golden st. john's wort

About Golden St. John's Wort

Hypericum frondosum · also called Golden St. John's Wort, Cedarglade St. Johnswort · flowering

Hypericum frondosum is a compact native US shrub famous for its large, showy golden-yellow flowers with prominent stamens in midsummer. Exceptionally adaptable and drought-tolerant once established, it suits borders, rock gardens, and naturalistic landscapes. The cultivar 'Sunburst' is widely grown for its superior bloom display. Hardy in zones 5–8.

Cold limit: USDA 5-8 · RHS H6 (-29°C to 38°C)

Watch for — Phytophthora dieback: Wet soil combined with warm temperatures can trigger Phytophthora root and collar rot. No chemical cure; prevention via drainage is critical. Remove infected plants.

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

Yes — golden st. john's wort is genuinely cold hardy. Rated RHS H6 and USDA 5-8, 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 5-8 — 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 about −20 to −15 °C. Golden St. John's Wort is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 5-8 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 golden 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.

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

Is golden st. john's wort cold hardy?

Yes — golden st. john's wort is genuinely cold hardy. Rated RHS H6 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Golden St. John's Wort is hardy across USDA 5-8; 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 golden st. john's wort can survive?

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

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

Golden St. John's Wort is rated USDA 5-8 and RHS H6 — Hardy throughout the UK and northern Europe.

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

Plant it out within USDA 5-8 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 golden 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.