Cold hardiness & minimum temperature

Is Spider Milkweed (Asclepias asperula)cold hardy? Hardiness zone & min temp

Also called Spider Milkweed, Antelope Horns, Antelopehorn Milkweed, Spider Antelope Horns.

More about spider milkweed

About Spider Milkweed

Asclepias asperula · also called Spider Milkweed, Antelope Horns · flowering

Spider Milkweed is a low-growing native perennial of the US Southwest and Great Plains, prized for its unusual greenish-white flower clusters with maroon markings that resemble spider legs. A xeric species deeply rooted in hot, dry prairie and desert grassland habitats, it is an important Monarch butterfly larval host and exceptional for water-wise native plant gardens.

Cold limit: USDA 5-10 · RHS H5 (-20 to 40°C)

What spider milkweed's hardiness rating actually means

Yes — spider milkweed is genuinely cold hardy. Rated RHS H5 and USDA 5-10, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 5-10 — 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 −15 to −10 °C. Spider Milkweed is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for spider milkweed as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 spider milkweed go outside or overwinter — and where?

Plant it out within USDA 5-10 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 spider milkweed can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Spider Milkweed hardiness — frequently asked questions

Is spider milkweed cold hardy?

Yes — spider milkweed is genuinely cold hardy. Rated RHS H5 and USDA 5-10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Spider Milkweed is hardy across USDA 5-10; 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 spider milkweed can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Spider Milkweed is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is spider milkweed?

Spider Milkweed is rated USDA 5-10 and RHS H5 — Hardy in most of the UK and in cold winters.

Can spider milkweed survive winter outside?

Plant it out within USDA 5-10 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 spider milkweed below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.