UK hardiness
Is Acorn squash hardy in the UK?
Cucurbita pepo
Acorn squash and the RHS hardiness rating
Acorn squash is rated RHS H2 — tender, meaning it withstands winter minimums of about 1 to 5°C. In practice that means it needs a frost-free greenhouse or indoors over winter — a UK frost will kill it. 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 acorn squash USDA hardiness guide.
Does UK region change it?
Because acorn squash 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 acorn squash in the UK
Overwintering acorn squash 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.
Acorn squash UK hardiness — frequently asked questions
Is acorn squash hardy in the UK?
Acorn squash is rated RHS H2 (tender, hardy to about 1 to 5°C). It is not winter-hardy anywhere in the UK and must be overwintered under cover.
Can acorn squash stay outside over winter in the UK?
No. Acorn squash 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 H2 mean?
RHS hardiness ratings run H1a (needs a heated glasshouse) to H7 (survives below -20°C). Acorn squash's rating, H2, means tender — it tolerates winter minimums of about 1 to 5°C. The rating is an absolute minimum, not an average.
How do I overwinter acorn squash in the UK?
Overwintering acorn squash 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 acorn squash survives?
Because acorn squash 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 acorn squash care
See the full acorn squash care guide, its temperature & humidity needs, and the US (USDA) hardiness version of this page.