Cold hardiness & minimum temperature

Is Moss Phlox (Phlox subulata)cold hardy? Hardiness zone & min temp

Also called Moss phlox, Creeping phlox, Moss pink, Ground pink.

More about moss phlox

About Moss Phlox

Phlox subulata · also called Moss phlox, Creeping phlox · flowering

Phlox subulata is a low, evergreen, mat-forming perennial native to rocky outcrops and open woodlands of the eastern United States. It blooms prolifically in mid-spring, smothering itself with small five-petalled flowers in shades of pink, white, lavender, or crimson. Full sun and sharply drained, moderately fertile soil are essential; cutting plants back by about one-third immediately after flowering keeps the mat dense and floriferous. Classified as non-toxic to dogs, cats, and horses by the ASPCA.

Cold limit: USDA 3-9 · RHS H6 (-26°C to 28°C)

What moss phlox's hardiness rating actually means

Yes — moss 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. Moss Phlox is built for winter — once established it takes hard frost and snow in its stride.

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

Moss Phlox hardiness — frequently asked questions

Is moss phlox cold hardy?

Yes — moss 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. Moss 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 moss phlox can survive?

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

What hardiness zone is moss phlox?

Moss Phlox is rated USDA 3-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can moss 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 moss 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.