Cold hardiness & minimum temperature

Is silver spike grass (Stipa calamagrostis)cold hardy? Hardiness zone & min temp

Also called silver spike grass, rough feather grass, spear grass, silver needle grass.

More about silver spike grass

About silver spike grass

Stipa calamagrostis · also called silver spike grass, rough feather grass · flowering

Silver spike grass is a cool-season ornamental grass producing arching clumps of narrow blue-green foliage and showy, silver-green feathery plumes from midsummer that age to warm tawny tones and persist through winter. Drought-tolerant and low-maintenance, it excels in sunny, well-drained borders, gravel gardens, and water-wise plantings. RHS Award of Garden Merit holder.

Cold limit: USDA 5–9 · RHS H6 (-20–35°C)

Watch for — Poor performance in humid climates: Stipa calamagrostis dislikes high summer humidity and warm wet nights. In the humid eastern US or maritime climates with mild wet winters, plants often decline rapidly. It is far better suited to dry, continental, or Mediterranean-climate gardens.

What silver spike grass's hardiness rating actually means

Yes — silver spike grass is genuinely cold hardy. Rated RHS H6 and USDA 5–9, 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 5–9 — 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. silver spike grass is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for silver spike grass 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 silver spike grass go outside or overwinter — and where?

Plant it out within USDA 5–9 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 silver spike grass can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

silver spike grass hardiness — frequently asked questions

Is silver spike grass cold hardy?

Yes — silver spike grass is genuinely cold hardy. Rated RHS H6 and USDA 5–9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. silver spike grass is hardy across USDA 5–9; 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 silver spike grass can survive?

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

What hardiness zone is silver spike grass?

silver spike grass is rated USDA 5–9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can silver spike grass survive winter outside?

Plant it out within USDA 5–9 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 silver spike grass 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.