Cold hardiness & minimum temperature

Is Long-Leaved Phlomis (Phlomis longifolia)cold hardy? Hardiness zone & min temp

Also called Long-leaved phlomis, Long-leaved Jerusalem sage.

More about long-leaved phlomis

About Long-Leaved Phlomis

Phlomis longifolia · also called Long-leaved phlomis, Long-leaved Jerusalem sage · flowering

Phlomis longifolia is an upright, grey-woolly shrub native to Turkey, Lebanon, and the eastern Mediterranean, recognisable by its unusually elongated, softly felted leaves and tall stems bearing whorls of bright yellow flowers in early summer. It is well suited to dry, sunny borders and gravel gardens where its bold, textural foliage provides year-round interest. Like all Mediterranean phlomis, it is intolerant of waterlogged soil and must have free drainage to thrive in wetter climates. Phlomis longifolia is not listed in the ASPCA database and is classified as mildly-toxic due to the absence of confirmed pet-safety information.

Cold limit: USDA 8-10 · RHS H4 (-5 to 38°C)

Watch for — Root rot from winter wet: The leading cause of plant loss in UK gardens; waterlogged, cold soils in winter rapidly cause fatal root and crown rot — sharp drainage, a grit mulch, and a sheltered site are the principal preventive measures.

What long-leaved phlomis's hardiness rating actually means

Yes — long-leaved phlomis 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. Long-Leaved Phlomis is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for long-leaved 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 long-leaved phlomis 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 long-leaved phlomis can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H4 figure above.

Long-Leaved Phlomis hardiness — frequently asked questions

Is long-leaved phlomis cold hardy?

Yes — long-leaved phlomis 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. Long-Leaved Phlomis 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 long-leaved phlomis can survive?

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

What hardiness zone is long-leaved phlomis?

Long-Leaved Phlomis is rated USDA 8-10 and RHS H4 — Hardy in an average winter across much of the temperate world.

Can long-leaved phlomis 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 long-leaved phlomis 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.