Cold hardiness & minimum temperature

Is Star of Bethlehem (Ornithogalum umbellatum)cold hardy? Hardiness zone & min temp

Also called Star of Bethlehem, Nap at Noon, Eleven O'Clock Lady.

More about star of bethlehem

About Star of Bethlehem

Ornithogalum umbellatum · also called Star of Bethlehem, Nap at Noon · flowering

A small, spreading bulb producing clusters of white star-shaped flowers with a green stripe on the reverse of each tepal, opening only in sunshine (hence 'Nap at Noon'). Naturalises vigorously and can become invasive in lawns and borders in favourable climates. Hardy in zones 4–9. All parts contain cardiac glycosides and are toxic to pets and humans.

Cold limit: USDA 4-9 · RHS H5 (-25°C to 25°C; dormant in summer)

What star of bethlehem's hardiness rating actually means

Yes — star of bethlehem is genuinely cold hardy. Rated RHS H5 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 4-9 — 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 −15 to −10 °C. Star of Bethlehem is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for star of bethlehem as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 star of bethlehem go outside or overwinter — and where?

Plant it out within USDA 4-9 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 star of bethlehem can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Star of Bethlehem hardiness — frequently asked questions

Is star of bethlehem cold hardy?

Yes — star of bethlehem is genuinely cold hardy. Rated RHS H5 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Star of Bethlehem is hardy across USDA 4-9; 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 star of bethlehem can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Star of Bethlehem is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is star of bethlehem?

Star of Bethlehem is rated USDA 4-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can star of bethlehem survive winter outside?

Plant it out within USDA 4-9 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 star of bethlehem below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.