Cold hardiness & minimum temperature

Is Adzuki Bean (Vigna angularis)cold hardy? Hardiness zone & min temp

Also called Adzuki Bean, Azuki Bean, Red Bean, Feijão Vermelho.

More about adzuki bean

About Adzuki Bean

Vigna angularis · also called Adzuki Bean, Azuki Bean · edible

Adzuki bean is a small, red-seeded annual legume prized in East Asian cuisine — the sweet red paste in mochi and anpan is made from adzuki. Slower-maturing than mung bean at 90–120 days, it tolerates cooler growing conditions than most tropical legumes, making it more viable in temperate gardens and polytunnels.

Cold limit: USDA 5-9 (grown as warm-season annual) · RHS H2 (15–30°C)

What adzuki bean's hardiness rating actually means

Hardiness works differently for adzuki bean: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". Its RHS rating of H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 5-9 (grown as warm-season annual) — 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

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

Concretely, for adzuki bean as it gets too cold:

Light frost (around 0 to −2 °C) damages or kills tender summer crops outright; cold-hardy types take a few degrees of frost.
The plant does not "survive winter" — its life cycle simply ends, by design, when frost arrives or it finishes cropping.
A surprise late spring frost can also kill young transplants set out too early, before the season even starts.

Can adzuki bean go outside or overwinter — and where?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost.
In short-season zones, start it indoors or under cover to stretch the effective growing window.
Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

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 adzuki bean can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline adzuki bean

Adzuki Bean is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks.
Have row cover ready for an unexpected late spring or early autumn frost.
Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.

Adzuki Bean hardiness — frequently asked questions

Is adzuki bean cold hardy?

Hardiness works differently for adzuki bean: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". A seasonal crop, not a perennial. Adzuki Bean is grown 5-9 (grown as warm-season annual); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature adzuki bean can survive?

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

What hardiness zone is adzuki bean?

Adzuki Bean is rated USDA 5-9 (grown as warm-season annual) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can adzuki bean survive winter outside?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost. In short-season zones, start it indoors or under cover to stretch the effective growing window. Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

How do I protect adzuki bean from frost?

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks. Have row cover ready for an unexpected late spring or early autumn frost. Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.