Cold hardiness & minimum temperature

Is Mondo Grass (Ophiopogon japonicus)cold hardy? Hardiness zone & min temp

Also called mondo grass, monkey grass, dwarf lilyturf.

More about mondo grass

About Mondo Grass

Ophiopogon japonicus · also called mondo grass, monkey grass · houseplant

Ophiopogon japonicus is a tough, grass-like evergreen perennial (a lily relative, not a true grass) forming dense clumps of dark green strappy foliage. It tolerates shade, spreads slowly by stolons, and bears small lilac-white summer flowers followed by blue berries. Widely used as a slow groundcover, edging or low-maintenance container plant indoors and out.

Cold limit: USDA 7-11 (outdoor in mild zones; houseplant elsewhere) · RHS H4 (15 to 27°C)

Watch for — Tatty winter foliage: Cold or wind can brown leaf tips in marginal areas. Trim or mow back damaged foliage in early spring to refresh the clump.

What mondo grass's hardiness rating actually means

Yes — mondo grass is genuinely cold hardy. Rated RHS H4 and USDA 7-11 (outdoor in mild zones; houseplant elsewhere), it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 7-11 (outdoor in mild zones; houseplant elsewhere) — 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 −10 to −5 °C. Mondo Grass is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for mondo grass as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 mondo grass go outside or overwinter — and where?

Plant it out within USDA 7-11 (outdoor in mild zones; houseplant elsewhere) 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 mondo grass can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Frost protection for borderline mondo grass

Mondo Grass 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.

Mondo Grass hardiness — frequently asked questions

Is mondo grass cold hardy?

Yes — mondo grass is genuinely cold hardy. Rated RHS H4 and USDA 7-11 (outdoor in mild zones; houseplant elsewhere), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Mondo Grass is hardy across USDA 7-11 (outdoor in mild zones; houseplant elsewhere); 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 mondo grass can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Mondo Grass is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is mondo grass?

Mondo Grass is rated USDA 7-11 (outdoor in mild zones; houseplant elsewhere) and RHS H4 — Hardy in an average winter across much of the temperate world.

Can mondo grass survive winter outside?

Plant it out within USDA 7-11 (outdoor in mild zones; houseplant elsewhere) 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 mondo grass 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.