Cold hardiness & minimum temperature

Is Ashy Broom (Genista cinerea)cold hardy? Hardiness zone & min temp

Also called Ashy Broom, Grey Broom, Cinerous Broom.

More about ashy broom

About Ashy Broom

Genista cinerea · also called Ashy Broom, Grey Broom · flowering

Ashy broom is a deciduous to semi-evergreen shrub native to the western Mediterranean, from Spain and southern France to northwest Africa. It thrives in full sun on fast-draining, poor to moderately fertile soils and is highly drought-tolerant once established, making it ideal for dry, sunny borders or gravel gardens. The most important care fact is to avoid hard pruning into old wood — trim only lightly after flowering to keep a tidy shape, as brooms resent cutting back to bare stems. Genista species contain quinolizidine alkaloids (cytisine) and are considered toxic to dogs and cats if ingested.

Cold limit: USDA 7-9 · RHS H5 (-10 to 35 °C)

What ashy broom's hardiness rating actually means

Yes — ashy broom is genuinely cold hardy. Rated RHS H5 and USDA 7-9, 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 7-9 — 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. Ashy Broom is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for ashy broom 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 ashy broom go outside or overwinter — and where?

Plant it out within USDA 7-9 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 ashy broom 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 ashy broom

Ashy Broom is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes.
Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness.
Shelter new growth from late spring frosts with fleece if a hard night is forecast.

Ashy Broom hardiness — frequently asked questions

Is ashy broom cold hardy?

Yes — ashy broom is genuinely cold hardy. Rated RHS H5 and USDA 7-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Ashy Broom is hardy across USDA 7-9; 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 ashy broom can survive?

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

What hardiness zone is ashy broom?

Ashy Broom is rated USDA 7-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can ashy broom survive winter outside?

Plant it out within USDA 7-9 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.

How do I protect ashy broom from frost?

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes. Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness. Shelter new growth from late spring frosts with fleece if a hard night is forecast.