Cold hardiness & minimum temperature

Is Yellow Mountain Heath (Phyllodoce glanduliflora)cold hardy? Hardiness zone & min temp

Also called Yellow Mountain Heath, Yellow Mountain Heather, Glandular-flowered Mountain Heath.

More about yellow mountain heath

About Yellow Mountain Heath

Phyllodoce glanduliflora · also called Yellow Mountain Heath, Yellow Mountain Heather · flowering

Phyllodoce glanduliflora is a low-growing evergreen subshrub native to alpine and subalpine zones of western North America from Oregon and Wyoming northward to Alaska, distinguished by its pale yellowish-white, glandular-hairy urn-shaped flowers in late spring and early summer. It naturally occurs above 1,500 m on moist, rocky or sandy slopes with peaty soils and requires cool summers, high humidity, and consistently moist acidic conditions. This is one of the most challenging Phyllodoce species to grow at lower elevations due to its requirement for cool temperatures year-round. Toxicity to pets has not been confirmed by ASPCA; as an Ericaceae member, treat with caution.

Cold limit: USDA 3-8 · RHS H7 (-35 to 20°C)

Watch for — Heat-induced collapse in lowland gardens: This snow-bed alpine cannot tolerate sustained summer temperatures above 20°C; plants rapidly wilt, desiccate, and die if exposed to warm lowland conditions without shade and consistent cool moisture — it is best suited to Scottish Highland gardens, high-altitude peat beds, or alpine troughs.

What yellow mountain heath's hardiness rating actually means

Yes — yellow mountain heath 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. Yellow Mountain Heath is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for yellow mountain heath 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 yellow mountain heath 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 yellow mountain heath can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Yellow Mountain Heath hardiness — frequently asked questions

Is yellow mountain heath cold hardy?

Yes — yellow mountain heath 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. Yellow Mountain Heath 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 yellow mountain heath can survive?

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

What hardiness zone is yellow mountain heath?

Yellow Mountain Heath is rated USDA 3-8 and RHS H7 — Hardy in the severest European continental winters.

Can yellow mountain heath 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 yellow mountain heath 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.