Cold hardiness & minimum temperature

Is Nasturtium officinale (Nasturtium officinale)cold hardy? Hardiness zone & min temp

Also called Watercress, Common Watercress, Water Nasturtium.

More about nasturtium officinale

About Nasturtium officinale

Nasturtium officinale · also called Watercress, Common Watercress · edible

Nasturtium officinale is watercress, a fast-growing peppery salad green in the cabbage family that thrives in cool, clean, flowing freshwater. It forms trailing stems of round leaves that root readily at every node, making it easy to grow in shallow streams, troughs or even a sunny windowsill jar. Home-grown cress avoids the contamination risk of wild stands.

Cold limit: USDA 5-11 (a cool-season hardy perennial that overwinters in mild areas and is grown as an annual where streams freeze) · RHS H5 (10-22°C)

Watch for — Bolting and bitterness in heat: Warm temperatures and long days make it flower and turn bitter and tough. Grow in the cool seasons, provide afternoon shade, and harvest young for the mildest, crispest leaves.

What nasturtium officinale's hardiness rating actually means

Hardiness works differently for nasturtium officinale: 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 5-11 (a cool-season hardy perennial that overwinters in mild areas and is grown as an annual where streams freeze) — 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 nasturtium officinale 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 nasturtium officinale 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 nasturtium officinale 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 nasturtium officinale

Nasturtium officinale 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.

Nasturtium officinale hardiness — frequently asked questions

Is nasturtium officinale cold hardy?

Hardiness works differently for nasturtium officinale: 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. Nasturtium officinale is grown 5-11 (a cool-season hardy perennial that overwinters in mild areas and is grown as an annual where streams freeze); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature nasturtium officinale 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 nasturtium officinale?

Nasturtium officinale is rated USDA 5-11 (a cool-season hardy perennial that overwinters in mild areas and is grown as an annual where streams freeze) and RHS H5 — Hardy in most of the UK and in cold winters.

Can nasturtium officinale 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 nasturtium officinale 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.