Cold hardiness & minimum temperature

Is Phlox subulata 'Emerald Blue' (Phlox subulata 'Emerald Blue')cold hardy? Hardiness zone & min temp

Also called Emerald Blue moss phlox, Creeping phlox.

More about phlox subulata 'emerald blue'

About Phlox subulata 'Emerald Blue'

Phlox subulata 'Emerald Blue' · also called Emerald Blue moss phlox, Creeping phlox · flowering

Phlox subulata 'Emerald Blue' is a low, evergreen creeping phlox that smothers itself in lavender-blue, star-shaped flowers in mid to late spring over needle-like green foliage. Mat-forming and drought-tolerant once established, it excels on banks, rock gardens, wall tops and as ground cover, knitting into a dense weed-suppressing carpet in full sun.

Cold limit: USDA 3-9 · RHS H7 (-34 to 27°C)

Watch for — Crown / stem rot in wet soil: Poor drainage and winter wet rot the carpet, leaving brown patches; plant in free-draining soil on slopes or raised sites.

What phlox subulata 'emerald blue''s hardiness rating actually means

Yes — phlox subulata 'emerald blue' is genuinely cold hardy. Rated RHS H7 and USDA 3-9, 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 3-9 — 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 below about −20 °C. Phlox subulata 'Emerald Blue' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for phlox subulata 'emerald blue' 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 phlox subulata 'emerald blue' go outside or overwinter — and where?

Plant it out within USDA 3-9 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 phlox subulata 'emerald blue' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Phlox subulata 'Emerald Blue' hardiness — frequently asked questions

Is phlox subulata 'emerald blue' cold hardy?

Yes — phlox subulata 'emerald blue' is genuinely cold hardy. Rated RHS H7 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Phlox subulata 'Emerald Blue' is hardy across USDA 3-9; 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 phlox subulata 'emerald blue' can survive?

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

What hardiness zone is phlox subulata 'emerald blue'?

Phlox subulata 'Emerald Blue' is rated USDA 3-9 and RHS H7 — Hardy in the severest European continental winters.

Can phlox subulata 'emerald blue' survive winter outside?

Plant it out within USDA 3-9 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 phlox subulata 'emerald blue' 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.