Cold hardiness & minimum temperature

Is Western Red Cedar (Thuja plicata)cold hardy? Hardiness zone & min temp

Also called Western Red Cedar, Giant Arborvitae, Giant Cedar, Pacific Red Cedar.

More about western red cedar

About Western Red Cedar

Thuja plicata · also called Western Red Cedar, Giant Arborvitae · flowering

Western Red Cedar is a majestic, fast-growing conifer native to the Pacific Northwest, one of the most important timber and cultural trees of the region. Its graceful, drooping branchlets carry flat, glossy, aromatic scale-like foliage. Adaptable to a wide range of soils, it makes an excellent large specimen, windbreak, or privacy hedge in zones 5–9.

Cold limit: USDA 5–9 · RHS H6 (-28°C to 30°C)

Watch for — Bagworm (Thyridopteryx ephemeraeformis): Caterpillars construct silk-and-foliage bags, feeding on and defoliating branches. Hand-pick bags from small trees in winter when bags are visible. Btk spray applied at caterpillar hatch in late spring is effective on young larvae.

What western red cedar's hardiness rating actually means

Yes — western red cedar is genuinely cold hardy. Rated RHS H6 and USDA 5–9, 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 5–9 — 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 −20 to −15 °C. Western Red Cedar is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for western red cedar 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 western red cedar go outside or overwinter — and where?

Plant it out within USDA 5–9 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 western red cedar can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Western Red Cedar hardiness — frequently asked questions

Is western red cedar cold hardy?

Yes — western red cedar is genuinely cold hardy. Rated RHS H6 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Western Red Cedar is hardy across USDA 5–9; 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 western red cedar can survive?

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

What hardiness zone is western red cedar?

Western Red Cedar is rated USDA 5–9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can western red cedar survive winter outside?

Plant it out within USDA 5–9 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.

What happens to western red cedar 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.