Cold hardiness & minimum temperature

Is Moonglow Juniper (Juniperus scopulorum 'Moonglow')cold hardy? Hardiness zone & min temp

Also called Moonglow Juniper, Silver Juniper.

More about moonglow juniper

About Moonglow Juniper

Juniperus scopulorum 'Moonglow' · also called Moonglow Juniper, Silver Juniper · flowering

Moonglow Juniper is a broad, upright pyramidal conifer reaching 4-6 m tall and 1.5-2.5 m wide, with luminous silver-blue foliage that holds its colour year-round. Fuller and wider than the columnar Rocky Mountain selections, it makes a dense screen or specimen. It needs full sun and well-drained soil and is robustly drought- and cold-tolerant.

Cold limit: USDA 3-9 (very cold-hardy) · RHS H6 (-35 to 38°C)

Watch for — Bagworms: Caterpillars build spindle-shaped bags and can defoliate junipers; hand-pick bags in winter or treat young larvae in early summer.

What moonglow juniper's hardiness rating actually means

Yes — moonglow juniper is genuinely cold hardy. Rated RHS H6 and USDA 3-9 (very cold-hardy), 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 3-9 (very cold-hardy) — 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. Moonglow Juniper is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for moonglow juniper 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 moonglow juniper go outside or overwinter — and where?

Plant it out within USDA 3-9 (very cold-hardy) 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 moonglow juniper can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Moonglow Juniper hardiness — frequently asked questions

Is moonglow juniper cold hardy?

Yes — moonglow juniper is genuinely cold hardy. Rated RHS H6 and USDA 3-9 (very cold-hardy), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Moonglow Juniper is hardy across USDA 3-9 (very cold-hardy); 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 moonglow juniper can survive?

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

What hardiness zone is moonglow juniper?

Moonglow Juniper is rated USDA 3-9 (very cold-hardy) and RHS H6 — Hardy throughout the UK and northern Europe.

Can moonglow juniper survive winter outside?

Plant it out within USDA 3-9 (very cold-hardy) 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 moonglow juniper 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.