Cold hardiness & minimum temperature

Is Rutabaga 'American Purple Top' (Brassica napus var. napobrassica 'American Purple Top')cold hardy? Hardiness zone & min temp

Also called American Purple Top rutabaga, purple top swede.

More about rutabaga 'american purple top'

About Rutabaga 'American Purple Top'

Brassica napus var. napobrassica 'American Purple Top' · also called American Purple Top rutabaga, purple top swede · edible

'American Purple Top' is a classic heirloom rutabaga with large, round roots, bright purple shoulders, and sweet yellow flesh that mellows after frost. A dependable storage variety, it is sown in mid to late summer for autumn and winter use over a 90-110 day season, and rewards fertile, evenly moist, well-drained soil with smooth, heavy roots.

Cold limit: USDA 3-9 (grown as a cool-season annual; frost-tolerant and sweetened by frost) · RHS H5 (10-18°C)

Watch for — Cracked or woody roots: Result from irregular watering, heat, or over-maturity. Maintain steady moisture, grow in the cool season, and harvest at moderate size after frost.

What rutabaga 'american purple top''s hardiness rating actually means

Hardiness works differently for rutabaga 'american purple top': 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 3-9 (grown as a cool-season annual; frost-tolerant and sweetened by 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 rutabaga 'american purple top' 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 rutabaga 'american purple top' 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 rutabaga 'american purple top' 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 rutabaga 'american purple top'

Rutabaga 'American Purple Top' 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.

Rutabaga 'American Purple Top' hardiness — frequently asked questions

Is rutabaga 'american purple top' cold hardy?

Hardiness works differently for rutabaga 'american purple top': 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. Rutabaga 'American Purple Top' is grown 3-9 (grown as a cool-season annual; frost-tolerant and sweetened by frost); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature rutabaga 'american purple top' 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 rutabaga 'american purple top'?

Rutabaga 'American Purple Top' is rated USDA 3-9 (grown as a cool-season annual; frost-tolerant and sweetened by frost) and RHS H5 — Hardy in most of the UK and in cold winters.

Can rutabaga 'american purple top' 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 rutabaga 'american purple top' 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.