Cold hardiness & minimum temperature

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

Also called Runner Bean, Scarlet Runner Bean, Multiflora Bean.

More about scarlet emperor runner bean

About Scarlet Emperor Runner Bean

Phaseolus coccineus · also called Runner Bean, Scarlet Runner Bean · edible

Scarlet Emperor is the UK's most popular runner bean variety, producing heavy crops of long, flat, stringy pods on vigorous vines clad in brilliant scarlet flowers. Highly productive and decorative. ASPCA classifies Phaseolus as non-toxic to dogs and cats. Best harvested young for finest texture.

Cold limit: USDA 7-11 (tender perennial typically grown as annual) · RHS H2 (15-25°C)

Watch for — Blossom drop in heat: Flowers drop without setting if daytime temperatures exceed 27°C. A fine mist at dusk and mulching roots can help; yields recover when temperatures cool.

What scarlet emperor runner bean's hardiness rating actually means

Hardiness works differently for scarlet emperor 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 7-11 (tender perennial typically grown as 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 scarlet emperor 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 emperor 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 emperor 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 emperor runner bean

Scarlet Emperor 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 Emperor Runner Bean hardiness — frequently asked questions

Is scarlet emperor runner bean cold hardy?

Hardiness works differently for scarlet emperor 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 Emperor Runner Bean is grown 7-11 (tender perennial typically grown as annual); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature scarlet emperor 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 emperor runner bean?

Scarlet Emperor Runner Bean is rated USDA 7-11 (tender perennial typically grown as annual) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can scarlet emperor 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 emperor 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.