Cold hardiness & minimum temperature

Is Crested Phlomis (Phlomis crinita)cold hardy? Hardiness zone & min temp

Also called Crested phlomis, Hairy phlomis.

More about crested phlomis

About Crested Phlomis

Phlomis crinita · also called Crested phlomis, Hairy phlomis · flowering

Phlomis crinita is a woolly-leaved sub-shrub native to the western Mediterranean, particularly Spain and North Africa, where it grows on dry rocky hillsides and scrubland. It thrives in full sun with sharply drained, low-fertility soil and shows excellent drought tolerance once established. The most important care fact is to avoid any supplemental watering or rich compost — too much moisture rots the crown, especially in winter. The pet-toxicity status is unknown and it is not listed by the ASPCA; treat as mildly toxic as a precaution.

Cold limit: USDA 7-10 · RHS H4 (-8 to 35°C)

Watch for — Crown rot: The most common cause of death, typically occurring in winter in poorly drained or heavy soil. Plant on a slope or raised bed and avoid mulching around the crown.

What crested phlomis's hardiness rating actually means

Yes — crested phlomis is genuinely cold hardy. Rated RHS H4 and USDA 7-10, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H4 means: Hardy in an average winter across much of the temperate world. On the US scale that maps to USDA 7-10 — 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 −10 to −5 °C. Crested Phlomis is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for crested phlomis as it gets too cold:

It tolerates winter lows to about −10 to −5 °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 crested phlomis go outside or overwinter — and where?

Plant it out within USDA 7-10 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 crested phlomis can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Frost protection for borderline crested phlomis

Crested Phlomis is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes.
Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness.
Shelter new growth from late spring frosts with fleece if a hard night is forecast.

Crested Phlomis hardiness — frequently asked questions

Is crested phlomis cold hardy?

Yes — crested phlomis is genuinely cold hardy. Rated RHS H4 and USDA 7-10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Crested Phlomis is hardy across USDA 7-10; 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 crested phlomis can survive?

Minimum survivable temperature is roughly about −10 to −5 °C. Crested Phlomis is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is crested phlomis?

Crested Phlomis is rated USDA 7-10 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can crested phlomis survive winter outside?

Plant it out within USDA 7-10 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.

How do I protect crested phlomis from frost?

At the cold edge of its range, mulch the root zone in late autumn to buffer the deepest freezes. Protect container specimens — pots freeze through far faster than open ground, costing roughly a zone of hardiness. Shelter new growth from late spring frosts with fleece if a hard night is forecast.