Cold hardiness & minimum temperature

Is Purple Jerusalem Sage (Phlomis purpurea)cold hardy? Hardiness zone & min temp

Also called Purple Jerusalem sage, Purple phlomis.

More about purple jerusalem sage

About Purple Jerusalem Sage

Phlomis purpurea · also called Purple Jerusalem sage, Purple phlomis · flowering

Phlomis purpurea is a handsome, upright evergreen shrub native to the dry hillsides and scrubland of southern Spain and Portugal, where it is one of the most widespread phlomis species in western Iberia. Its grey-white woolly leaves contrast beautifully with whorls of rosy-purple to lilac-pink flowers produced from late spring to early summer. Once established it is remarkably drought-tolerant, but adequate sun and free drainage are essential for long-term health. It is not listed on the ASPCA database and is classified as mildly-toxic due to insufficient confirmed pet-safety data.

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

Watch for — Root rot in cold, wet soils: Standing water around the crown in winter is fatal; improve drainage with grit mulch and avoid watering from late September onward in cool climates.

What purple jerusalem sage's hardiness rating actually means

Yes — purple jerusalem sage is genuinely cold hardy. Rated RHS H4 and USDA 8-10, 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 8-10 — 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. Purple Jerusalem Sage is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for purple jerusalem sage 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 purple jerusalem sage go outside or overwinter — and where?

Plant it out within USDA 8-10 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 purple jerusalem sage can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Purple Jerusalem Sage hardiness — frequently asked questions

Is purple jerusalem sage cold hardy?

Yes — purple jerusalem sage is genuinely cold hardy. Rated RHS H4 and USDA 8-10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Purple Jerusalem Sage is hardy across USDA 8-10; 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 purple jerusalem sage can survive?

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

What hardiness zone is purple jerusalem sage?

Purple Jerusalem Sage is rated USDA 8-10 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can purple jerusalem sage survive winter outside?

Plant it out within USDA 8-10 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.

What happens to purple jerusalem sage below its minimum temperature?

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.