Cold hardiness & minimum temperature

Is Emerald Green Arborvitae (Thuja occidentalis 'Smaragd')cold hardy? Hardiness zone & min temp

Also called Emerald Arborvitae, Smaragd Arborvitae, Emerald Green Thuja.

More about emerald green arborvitae

About Emerald Green Arborvitae

Thuja occidentalis 'Smaragd' · also called Emerald Arborvitae, Smaragd Arborvitae · flowering

Emerald Green Arborvitae is one of the most popular narrow, columnar evergreen conifers for hedging and screening, maintaining vibrant emerald-green colour year-round without bronzing in winter. Slow-growing and space-efficient, it is ideal for formal gardens, privacy screens, and small spaces. Thuja foliage contains thujone and is toxic to pets if ingested.

Cold limit: USDA 3-8 · RHS H7 (-30 to 30°C)

Watch for — Bagworms: Spindle-shaped bags on foliage in summer; hand-pick in autumn/winter or treat with Bt in spring.

What emerald green arborvitae's hardiness rating actually means

Yes — emerald green arborvitae is genuinely cold hardy. Rated RHS H7 and USDA 3-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 3-8 — 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 below about −20 °C. Emerald Green Arborvitae is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for emerald green arborvitae as it gets too cold:

It tolerates winter lows to about −20 °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 emerald green arborvitae go outside or overwinter — and where?

Plant it out within USDA 3-8 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 emerald green arborvitae can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Emerald Green Arborvitae hardiness — frequently asked questions

Is emerald green arborvitae cold hardy?

Yes — emerald green arborvitae is genuinely cold hardy. Rated RHS H7 and USDA 3-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Emerald Green Arborvitae is hardy across USDA 3-8; 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 emerald green arborvitae can survive?

Minimum survivable temperature is roughly below about −20 °C. Emerald Green Arborvitae is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is emerald green arborvitae?

Emerald Green Arborvitae is rated USDA 3-8 and RHS H7 — Hardy in the severest European continental winters.

Can emerald green arborvitae survive winter outside?

Plant it out within USDA 3-8 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 emerald green arborvitae below its minimum temperature?

It tolerates winter lows to about −20 °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.