UK hardiness
Is Key lime hardy in the UK?
Citrus aurantifolia
More about key lime in the UK
Key lime and the RHS hardiness rating
Key lime is rated RHS H1b — heated glasshouse — subtropical, meaning it withstands winter minimums of about 10 to 15°C. In practice that means it indoors over winter; can summer outdoors once nights are reliably mild. 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 key lime USDA hardiness guide.
Does UK region change it?
Because key lime is frost-tender, UK region matters less than the simple rule: it does not stay outdoors over winter anywhere in the UK. Treat any time outside as a summer holiday — bring it back indoors once nights drop toward 10°C, well before the first frost, and acclimatise it over a week each way so the leaves do not shock.
Overwintering key lime in the UK
Overwintering key lime in the UK means bringing it in: a bright, frost-free room or a heated glasshouse, watered sparingly while growth slows. Do not leave it against cold glass or near an unheated porch. Move it back out only after the last spring frost has passed for your area.
Key lime UK hardiness — frequently asked questions
Is key lime hardy in the UK?
Key lime is rated RHS H1b (heated glasshouse — subtropical, hardy to about 10 to 15°C). It is not winter-hardy anywhere in the UK and must be overwintered under cover.
Can key lime stay outside over winter in the UK?
No. Key lime is frost-tender — a UK frost will kill it. Bring it indoors or into a frost-free greenhouse before the first autumn frost and return it outside only after the last spring frost.
What does RHS H1b mean?
RHS hardiness ratings run H1a (needs a heated glasshouse) to H7 (survives below -20°C). Key lime's rating, H1b, means heated glasshouse — subtropical — it tolerates winter minimums of about 10 to 15°C. The rating is an absolute minimum, not an average.
How do I overwinter key lime in the UK?
Overwintering key lime in the UK means bringing it in: a bright, frost-free room or a heated glasshouse, watered sparingly while growth slows. Do not leave it against cold glass or near an unheated porch. Move it back out only after the last spring frost has passed for your area.
Does UK region change whether key lime survives?
Because key lime is frost-tender, UK region matters less than the simple rule: it does not stay outdoors over winter anywhere in the UK. Treat any time outside as a summer holiday — bring it back indoors once nights drop toward 10°C, well before the first frost, and acclimatise it over a week each way so the leaves do not shock.
More key lime care
See the full key lime care guide, its temperature & humidity needs, and the US (USDA) hardiness version of this page.