Cold hardiness & minimum temperature

Is Compacta Holly (Ilex crenata 'Compacta')cold hardy? Hardiness zone & min temp

Also called Compact Japanese Holly, Mound Japanese Holly.

More about compacta holly

About Compacta Holly

Ilex crenata 'Compacta' · also called Compact Japanese Holly, Mound Japanese Holly · flowering

Compacta is a rounded, densely branched Japanese holly with small glossy dark-green leaves, slightly larger and more vigorous than 'Helleri'. It takes full sun to part shade and demands acidic, well-drained soil. Reaching about 1.2-1.8 m, it shears into formal hedges and globes and serves as a reliable boxwood alternative resistant to boxwood blight.

Cold limit: USDA 5-8 · RHS H6 (-23 to 32°C)

Watch for — Overgrown legginess: Neglected plants can thin out at the base; this cultivar tolerates hard rejuvenation pruning in late winter to restore density.

What compacta holly's hardiness rating actually means

Yes — compacta holly is genuinely cold hardy. Rated RHS H6 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. 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 −20 to −15 °C. Compacta Holly is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for compacta holly as it gets too cold:

It tolerates winter lows to about −20 to −15 °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 compacta holly 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 compacta holly can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Compacta Holly hardiness — frequently asked questions

Is compacta holly cold hardy?

Yes — compacta holly is genuinely cold hardy. Rated RHS H6 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Compacta Holly 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 compacta holly can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Compacta Holly is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is compacta holly?

Compacta Holly is rated USDA 5-8 and RHS H6 — Hardy throughout the UK and northern Europe.

Can compacta holly 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 compacta holly below its minimum temperature?

It tolerates winter lows to about −20 to −15 °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.