Cold hardiness & minimum temperature

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

Also called Emerald Blue Creeping Phlox, Emerald Blue Moss Phlox, Blue Creeping Phlox.

More about emerald blue creeping phlox

About Emerald Blue Creeping Phlox

Phlox subulata 'Emerald Blue' · also called Emerald Blue Creeping Phlox, Emerald Blue Moss Phlox · flowering

A vigorous, evergreen ground-hugging perennial smothered in lavender-blue, five-petalled flowers in mid-spring, obscuring the needle-like foliage entirely. Forms a dense, weed-suppressing mat on slopes, rock gardens, and retaining walls. Extremely cold hardy and drought-tolerant once established. ASPCA-confirmed non-toxic to cats, dogs, and horses.

Cold limit: USDA 3–9 · RHS H6 (-29–35°C)

Watch for — Crown rot / root rot: The most common cause of failure: wet, poorly drained soil especially in winter. Ensure planting site drains freely, use raised or sloping ground, and avoid mulching heavily over the crown. Remove and discard affected plants; do not replant in the same spot.

What emerald blue creeping phlox's hardiness rating actually means

Yes — emerald blue creeping phlox is genuinely cold hardy. Rated RHS H6 and USDA 3–9, 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 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 about −20 to −15 °C. Emerald Blue Creeping Phlox is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for emerald blue creeping phlox 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 emerald blue creeping phlox 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 emerald blue creeping phlox can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Emerald Blue Creeping Phlox hardiness — frequently asked questions

Is emerald blue creeping phlox cold hardy?

Yes — emerald blue creeping phlox is genuinely cold hardy. Rated RHS H6 and USDA 3–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Emerald Blue Creeping Phlox 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 emerald blue creeping phlox can survive?

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

What hardiness zone is emerald blue creeping phlox?

Emerald Blue Creeping Phlox is rated USDA 3–9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can emerald blue creeping phlox 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 emerald blue creeping phlox 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.