UK hardiness
Is Spiraea thunbergii 'Ogon' hardy in the UK?
Spiraea thunbergii 'Ogon'
More about spiraea thunbergii 'ogon' in the UK
Spiraea thunbergii 'Ogon' and the RHS hardiness rating
Spiraea thunbergii 'Ogon' is rated RHS H6 — hardy in a very cold winter, meaning it withstands winter minimums of about -20 to -15°C. In practice that means it fully hardy throughout the UK and into northern Europe. The RHS rating describes an absolute minimum temperature, not an average: a single hard frost below its band is what does the damage, so the question is always "what is the coldest night my garden gets?", not "what is a typical winter here?".
This follows the RHS plant hardiness rating system (H1a–H7), the UK standard. For the US growing-zone view, see the spiraea thunbergii 'ogon' USDA hardiness guide.
Does UK region change it?
UK winters vary far more by locality than by latitude. Mild western and coastal areas (the south-west, Pembrokeshire, western Scotland's coast) and urban heat islands run several degrees warmer than inland frost pockets, valleys, and exposed eastern sites at the same latitude. A plant marginal on its RHS rating often survives in a sheltered town garden but fails 20 miles inland — so judge by your own coldest recorded night and microclimate (a south-facing wall, a courtyard) rather than the regional average.
Overwintering spiraea thunbergii 'ogon' in the UK
For a borderline-hardy plant, the UK winter killers are not just cold air but cold wet roots and wind. Improve drainage before winter, mulch the root zone, move containers to a sheltered spot or against a warm wall, and use horticultural fleece on hard-frost nights. Established plants in free-draining soil take far more cold than a recently planted one in heavy, wet ground.
Spiraea thunbergii 'Ogon' UK hardiness — frequently asked questions
Is spiraea thunbergii 'ogon' hardy in the UK?
Spiraea thunbergii 'Ogon' is rated RHS H6 (hardy in a very cold winter, hardy to about -20 to -15°C). It fully hardy throughout the UK and into northern Europe.
Can spiraea thunbergii 'ogon' stay outside over winter in the UK?
In most of the UK, yes, if your garden's coldest night stays within its RHS H6 band (around -20 to -15°C). In colder inland or northern gardens, give it a sheltered spot, sharp drainage, and fleece on hard-frost nights.
What does RHS H6 mean?
RHS hardiness ratings run H1a (needs a heated glasshouse) to H7 (survives below -20°C). Spiraea thunbergii 'Ogon''s rating, H6, means hardy in a very cold winter — it tolerates winter minimums of about -20 to -15°C. The rating is an absolute minimum, not an average.
How do I overwinter spiraea thunbergii 'ogon' in the UK?
For a borderline-hardy plant, the UK winter killers are not just cold air but cold wet roots and wind. Improve drainage before winter, mulch the root zone, move containers to a sheltered spot or against a warm wall, and use horticultural fleece on hard-frost nights. Established plants in free-draining soil take far more cold than a recently planted one in heavy, wet ground.
Does UK region change whether spiraea thunbergii 'ogon' survives?
UK winters vary far more by locality than by latitude. Mild western and coastal areas (the south-west, Pembrokeshire, western Scotland's coast) and urban heat islands run several degrees warmer than inland frost pockets, valleys, and exposed eastern sites at the same latitude. A plant marginal on its RHS rating often survives in a sheltered town garden but fails 20 miles inland — so judge by your own coldest recorded night and microclimate (a south-facing wall, a courtyard) rather than the regional average.
More spiraea thunbergii 'ogon' care
See the full spiraea thunbergii 'ogon' care guide, its temperature & humidity needs, and the US (USDA) hardiness version of this page.