Cold hardiness & minimum temperature

Is Rose of Sharon 'Diana' (Hibiscus syriacus 'Diana')cold hardy? Hardiness zone & min temp

Also called White Rose of Sharon.

More about rose of sharon 'diana'

About Rose of Sharon 'Diana'

Hibiscus syriacus 'Diana' · also called White Rose of Sharon · flowering

Hibiscus syriacus 'Diana' is a US National Arboretum selection bearing very large, pure-white single flowers without the usual red throat. The blooms stay open longer into the evening, and the plant is largely sterile, so it self-seeds little. It flowers heavily from midsummer to autumn on an upright shrub, making a clean, luminous late-season feature.

Cold limit: USDA 5-9 · RHS H5 (-26 to 35°C)

Watch for — Late spring emergence: Like all rose of Sharon it leafs out late, prompting fears it has died over winter. Check stems for green cambium and wait; growth typically resumes in late spring.

What rose of sharon 'diana''s hardiness rating actually means

Yes — rose of sharon 'diana' 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. Rose of Sharon 'Diana' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for rose of sharon 'diana' 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 rose of sharon 'diana' 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 rose of sharon 'diana' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Rose of Sharon 'Diana' hardiness — frequently asked questions

Is rose of sharon 'diana' cold hardy?

Yes — rose of sharon 'diana' 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. Rose of Sharon 'Diana' 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 rose of sharon 'diana' can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Rose of Sharon 'Diana' is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is rose of sharon 'diana'?

Rose of Sharon 'Diana' is rated USDA 5-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can rose of sharon 'diana' 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 rose of sharon 'diana' 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.