Cold hardiness & minimum temperature

Is Mustard Greens 'Red Giant' (Brassica juncea var. rugosa 'Red Giant')cold hardy? Hardiness zone & min temp

Also called Red Giant mustard, red mustard greens.

More about mustard greens 'red giant'

About Mustard Greens 'Red Giant'

Brassica juncea var. rugosa 'Red Giant' · also called Red Giant mustard, red mustard greens · edible

Mustard greens 'Red Giant' is a vigorous Japanese mustard with large, savoyed purple-red leaves and a hot, peppery bite that mellows with cooking. Fast to crop at 40-45 days, it suits cut-and-come-again or full heads. A cool-season brassica, it grows best in spring and autumn; heat and long days drive it quickly to bolt.

Cold limit: USDA Cool-season annual, zones 2-11; mature leaves tolerate frost to about -6°C, often sweetening after a light frost · RHS H5 (frost-hardy leaves; grown as an annual) (10-24°C)

What mustard greens 'red giant''s hardiness rating actually means

Hardiness works differently for mustard greens 'red giant': 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 H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA Cool-season annual, zones 2-11; mature leaves tolerate frost to about -6°C, often sweetening after a light frost — 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 mustard greens 'red giant' 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 mustard greens 'red giant' 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 mustard greens 'red giant' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Frost protection for borderline mustard greens 'red giant'

Mustard Greens 'Red Giant' 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.

Mustard Greens 'Red Giant' hardiness — frequently asked questions

Is mustard greens 'red giant' cold hardy?

Hardiness works differently for mustard greens 'red giant': 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. Mustard Greens 'Red Giant' is grown Cool-season annual, zones 2-11; mature leaves tolerate frost to about -6°C, often sweetening after a light frost; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature mustard greens 'red giant' 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 mustard greens 'red giant'?

Mustard Greens 'Red Giant' is rated USDA Cool-season annual, zones 2-11; mature leaves tolerate frost to about -6°C, often sweetening after a light frost and RHS H5 — Hardy in most of the UK and in cold winters.

Can mustard greens 'red giant' 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 mustard greens 'red giant' 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.