Cold hardiness & minimum temperature

Is Rosinweed (Silphium integrifolium)cold hardy? Hardiness zone & min temp

Also called Rosinweed, Entire-leaved rosinweed, Prairie rosinweed.

More about rosinweed

About Rosinweed

Silphium integrifolium · also called Rosinweed, Entire-leaved rosinweed · flowering

Silphium integrifolium is a robust native perennial of central and eastern US prairies, producing opposite or whorled rough-textured entire leaves along stout stems and a profusion of clear yellow daisy flowers from midsummer to early autumn. It is one of the more compact and garden-adaptable Silphium species, reaching a manageable 90-150 cm (3-5 ft), and has attracted research interest as a potential oilseed crop. Like other rosinweeds, it is deeply rooted and extremely drought-tolerant once established. Silphium integrifolium is not listed by the ASPCA as toxic to cats or dogs.

Cold limit: USDA 4-9 · RHS H6 (-30 to 38°C)

Watch for — Crown rot in wet soils: Extended winter waterlogging or poorly drained summer soils can cause crown rot. Improve drainage before planting; on heavy clay, raise the planting level slightly or add grit to the planting hole.

What rosinweed's hardiness rating actually means

Yes — rosinweed is genuinely cold hardy. Rated RHS H6 and USDA 4-9, 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 4-9 — 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. Rosinweed is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for rosinweed 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 rosinweed go outside or overwinter — and where?

Plant it out within USDA 4-9 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 rosinweed can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Rosinweed hardiness — frequently asked questions

Is rosinweed cold hardy?

Yes — rosinweed is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Rosinweed is hardy across USDA 4-9; 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 rosinweed can survive?

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

What hardiness zone is rosinweed?

Rosinweed is rated USDA 4-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can rosinweed survive winter outside?

Plant it out within USDA 4-9 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 rosinweed 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.