Cold hardiness & minimum temperature

Is Columnae Snow-in-Summer (Cerastium tomentosum 'Columnae')cold hardy? Hardiness zone & min temp

Also called Columnae Snow-in-Summer, Snow-in-Summer Columnae.

More about columnae snow-in-summer

About Columnae Snow-in-Summer

Cerastium tomentosum 'Columnae' · also called Columnae Snow-in-Summer, Snow-in-Summer Columnae · flowering

Columnae Snow-in-Summer is a selected cultivar of the classic silver-leaved ground cover, forming a tight, non-invasive mat of woolly grey-white foliage smothered in pure white flowers in late spring and early summer. Less rampant than the species, it is ideal for rock gardens, dry walls, and sunny borders where it provides year-round silver texture.

Cold limit: USDA 3-7 · RHS H7 (−25°C to 32°C)

Watch for — Crown rot in wet or heavy soils: The most serious risk; Cerastium tomentosum 'Columnae' is highly intolerant of wet roots, especially in winter. Ensure very sharp drainage before planting. Raise beds or plant on slopes and in rock crevices. Remove any decaying material promptly and do not mulch over the crown.

What columnae snow-in-summer's hardiness rating actually means

Yes — columnae snow-in-summer is genuinely cold hardy. Rated RHS H7 and USDA 3-7, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 3-7 — 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 below about −20 °C. Columnae Snow-in-Summer is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for columnae snow-in-summer as it gets too cold:

It tolerates winter lows to about −20 °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 columnae snow-in-summer go outside or overwinter — and where?

Plant it out within USDA 3-7 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 columnae snow-in-summer can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Columnae Snow-in-Summer hardiness — frequently asked questions

Is columnae snow-in-summer cold hardy?

Yes — columnae snow-in-summer is genuinely cold hardy. Rated RHS H7 and USDA 3-7, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Columnae Snow-in-Summer is hardy across USDA 3-7; 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 columnae snow-in-summer can survive?

Minimum survivable temperature is roughly below about −20 °C. Columnae Snow-in-Summer is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is columnae snow-in-summer?

Columnae Snow-in-Summer is rated USDA 3-7 and RHS H7 — Hardy in the severest European continental winters.

Can columnae snow-in-summer survive winter outside?

Plant it out within USDA 3-7 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 columnae snow-in-summer below its minimum temperature?

It tolerates winter lows to about −20 °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.