Cold hardiness & minimum temperature

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

Also called Common Star of Bethlehem, Nap-at-noon, Eleven-o'clock Lady.

More about star of bethlehem

About Star of Bethlehem

Ornithogalum umbellatum · also called Common Star of Bethlehem, Nap-at-noon · flowering

Star of Bethlehem is a compact European and Middle Eastern Asparagaceae bulb producing clusters of bright white, star-shaped flowers with distinctive green stripes on the outer petals in spring. It naturalises easily but can become invasive. The ASPCA lists Ornithogalum as toxic to dogs, cats, and horses.

Cold limit: USDA 4-9 · RHS H7 (5-25°C)

Watch for — Failure to flower indoors: Requires a cold vernalisation period to initiate blooming; bulbs brought in for forcing must first receive 12-16 weeks at 2-7°C.

What star of bethlehem's hardiness rating actually means

Yes — star of bethlehem is genuinely cold hardy. Rated RHS H7 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental 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 below about −20 °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 −20 °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 H7 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 H7 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 below about −20 °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 H7 — Hardy in the severest European continental 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 −20 °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.