Cold hardiness & minimum temperature

Is Shrubby St John's Wort (Hypericum calycinum)cold hardy? Hardiness zone & min temp

Also called Rose of Sharon, Aaron's beard, creeping St John's wort.

More about shrubby st john's wort

About Shrubby St John's Wort

Hypericum calycinum · also called Rose of Sharon, Aaron's beard · flowering

Hypericum calycinum is a low, spreading evergreen-to-semi-evergreen subshrub grown as tough groundcover. It bears large golden-yellow flowers with prominent boss-like stamens through summer and roots from spreading stolons to knit dense, weed-smothering cover. Adaptable to sun or shade and poor, dry soil, it is vigorous to the point of becoming invasive.

Cold limit: USDA 5-9 · RHS H5 (-15 to 30°C)

What shrubby st john's wort's hardiness rating actually means

Yes — shrubby st john's wort is genuinely cold hardy. Rated RHS H5 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. 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 −15 to −10 °C. Shrubby St John's Wort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for shrubby st john's wort as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 shrubby 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 shrubby st john's wort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Shrubby St John's Wort hardiness — frequently asked questions

Is shrubby st john's wort cold hardy?

Yes — shrubby st john's wort is genuinely cold hardy. Rated RHS H5 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Shrubby 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 shrubby st john's wort can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Shrubby St John's Wort is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is shrubby st john's wort?

Shrubby St John's Wort is rated USDA 5-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can shrubby 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 shrubby st john's wort below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.