Cold hardiness & minimum temperature

Is 'Scarlet Runner' Bean (Phaseolus coccineus 'Scarlet Emperor')cold hardy? Hardiness zone & min temp

Also called Runner bean, Scarlet runner bean.

More about 'scarlet runner' bean

About 'Scarlet Runner' Bean

Phaseolus coccineus 'Scarlet Emperor' · also called Runner bean, Scarlet runner bean · edible

'Scarlet Emperor' is a vigorous climbing runner bean (Phaseolus coccineus) prized for both its showy scarlet flowers and long, flat green pods. A tender perennial grown as an annual, it twines several metres up supports in a single season. Sow after frost, train up canes or netting, and pick pods young for the most tender, stringless beans.

Cold limit: USDA Grown as annual in zones 3-11; perennial roots only in 7-11 (frost-tender) · RHS H2 (13-26°C)

What 'scarlet runner' bean's hardiness rating actually means

Hardiness works differently for 'scarlet runner' 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 Grown as annual in zones 3-11; perennial roots only in 7-11 (frost-tender) — 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 'scarlet runner' 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 'scarlet runner' 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 'scarlet runner' 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 'scarlet runner' bean

'Scarlet Runner' 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.

'Scarlet Runner' Bean hardiness — frequently asked questions

Is 'scarlet runner' bean cold hardy?

Hardiness works differently for 'scarlet runner' 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. 'Scarlet Runner' Bean is grown Grown as annual in zones 3-11; perennial roots only in 7-11 (frost-tender); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature 'scarlet runner' 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 'scarlet runner' bean?

'Scarlet Runner' Bean is rated USDA Grown as annual in zones 3-11; perennial roots only in 7-11 (frost-tender) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can 'scarlet runner' 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 'scarlet runner' 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.