Cold hardiness & minimum temperature

Is Sickle-leaved Hare's-ear (Bupleurum falcatum)cold hardy? Hardiness zone & min temp

Also called Sickle-leaved Hare's-ear, Sickle Hare's Ear, Falcate Thorow-wax.

More about sickle-leaved hare's-ear

About Sickle-leaved Hare's-ear

Bupleurum falcatum · also called Sickle-leaved Hare's-ear, Sickle Hare's Ear · flowering

Bupleurum falcatum is an upright perennial in the carrot family (Apiaceae), native to dry, calcareous grasslands and stony slopes across central and southern Europe, with a handful of historical sites in Essex in the UK where it is now extremely rare. It bears small compound umbels of yellow-green flowers on branching stems from midsummer into autumn, and is highly tolerant of drought and poor, stony soil once established. The most important care requirement is sharp drainage — waterlogged conditions are fatal. It is not listed as toxic by the ASPCA; however, some Apiaceae relatives are toxic, so treat with caution.

Cold limit: USDA 5-8 · RHS H5 (-15 to 28°C)

What sickle-leaved hare's-ear's hardiness rating actually means

Yes — sickle-leaved hare's-ear is genuinely cold hardy. Rated RHS H5 and USDA 5-8, 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 5-8 — 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. Sickle-leaved Hare's-ear is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for sickle-leaved hare's-ear 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 sickle-leaved hare's-ear go outside or overwinter — and where?

Plant it out within USDA 5-8 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 sickle-leaved hare's-ear can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Sickle-leaved Hare's-ear hardiness — frequently asked questions

Is sickle-leaved hare's-ear cold hardy?

Yes — sickle-leaved hare's-ear is genuinely cold hardy. Rated RHS H5 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Sickle-leaved Hare's-ear is hardy across USDA 5-8; 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 sickle-leaved hare's-ear can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Sickle-leaved Hare's-ear is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is sickle-leaved hare's-ear?

Sickle-leaved Hare's-ear is rated USDA 5-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can sickle-leaved hare's-ear survive winter outside?

Plant it out within USDA 5-8 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 sickle-leaved hare's-ear 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.