UK hardiness
Is Black Gram hardy in the UK?
Vigna mungo
More about black gram in the UK
Black Gram and the RHS hardiness rating
Black Gram 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 black gram USDA hardiness guide.
Does UK region change it?
Because black gram 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 black gram in the UK
Overwintering black gram 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.
Black Gram UK hardiness — frequently asked questions
Is black gram hardy in the UK?
Black Gram 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 black gram stay outside over winter in the UK?
No. Black Gram 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). Black Gram'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 black gram in the UK?
Overwintering black gram 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 black gram survives?
Because black gram 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 black gram care
See the full black gram care guide, its temperature & humidity needs, and the US (USDA) hardiness version of this page.