Cold hardiness & minimum temperature

Is Black Mondo Grass (Ophiopogon planiscapus 'Nigrescens')cold hardy? Hardiness zone & min temp

Also called black mondo grass, black lilyturf.

More about black mondo grass

About Black Mondo Grass

Ophiopogon planiscapus 'Nigrescens' · also called black mondo grass, black lilyturf · houseplant

Ophiopogon planiscapus 'Nigrescens' is a striking evergreen perennial grown for its almost-black, strappy foliage, among the darkest of any garden plant. It forms slow-spreading clumps, bears pale lilac summer flowers and glossy black berries, and combines dramatically with silver or chartreuse plantings. Slow-growing and shade-tolerant, it suits edging, gravel gardens and containers.

Cold limit: USDA 6-10 (outdoor hardy) · RHS H5 (12 to 27°C)

Watch for — Root/crown rot in wet soil: Heavy, waterlogged ground rots the crown. Ensure free drainage and avoid winter-wet, compacted positions.

What black mondo grass's hardiness rating actually means

Yes — black mondo grass is genuinely cold hardy. Rated RHS H5 and USDA 6-10 (outdoor hardy), 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 6-10 (outdoor hardy) — 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. Black Mondo Grass is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for black mondo grass 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 black mondo grass go outside or overwinter — and where?

Plant it out within USDA 6-10 (outdoor hardy) 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 black mondo grass can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Black Mondo Grass hardiness — frequently asked questions

Is black mondo grass cold hardy?

Yes — black mondo grass is genuinely cold hardy. Rated RHS H5 and USDA 6-10 (outdoor hardy), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Black Mondo Grass is hardy across USDA 6-10 (outdoor hardy); 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 black mondo grass can survive?

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

What hardiness zone is black mondo grass?

Black Mondo Grass is rated USDA 6-10 (outdoor hardy) and RHS H5 — Hardy in most of the UK and in cold winters.

Can black mondo grass survive winter outside?

Plant it out within USDA 6-10 (outdoor hardy) 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 black mondo grass 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.