Cold hardiness & minimum temperature

Is Rocket candytuft (Iberis amara)cold hardy? Hardiness zone & min temp

Also called Rocket candytuft, bitter candytuft, wild candytuft.

More about rocket candytuft

About Rocket candytuft

Iberis amara · also called Rocket candytuft, bitter candytuft · flowering

Rocket candytuft is a cool-season hardy annual bearing elongated, fragrant white flower spikes that lengthen as blooms open from the base upward — giving the 'rocket' form distinct from globe candytuft. Native to chalk downlands of southern England and Europe, it tolerates poor, alkaline soils and is excellent for cutting and wildflower plantings.

Cold limit: USDA 3-9 · RHS H6 (5–20°C)

What rocket candytuft's hardiness rating actually means

Yes — rocket candytuft is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 3-9 — 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

Minimum survivable temperature is roughly about −20 to −15 °C. Rocket candytuft is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for rocket candytuft as it gets too cold:

It tolerates winter lows to about −20 to −15 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can rocket candytuft go outside or overwinter — and where?

Plant it out within USDA 3-9 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 rocket candytuft can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Rocket candytuft hardiness — frequently asked questions

Is rocket candytuft cold hardy?

Yes — rocket candytuft is genuinely cold hardy. Rated RHS H6 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Rocket candytuft is hardy across USDA 3-9; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature rocket candytuft can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Rocket candytuft is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is rocket candytuft?

Rocket candytuft is rated USDA 3-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can rocket candytuft survive winter outside?

Plant it out within USDA 3-9 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to rocket candytuft below its minimum temperature?

It tolerates winter lows to about −20 to −15 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.