Cold hardiness & minimum temperature

Is Downy Painted Cup (Castilleja sessiliflora)cold hardy? Hardiness zone & min temp

Also called Downy painted cup, Downy Indian paintbrush, Downy paintedcup.

More about downy painted cup

About Downy Painted Cup

Castilleja sessiliflora · also called Downy painted cup, Downy Indian paintbrush · flowering

Castilleja sessiliflora is a low-growing prairie perennial native to the Great Plains of North America, from southern Canada south through the central US to northern Mexico. It is hemiparasitic, tapping the roots of native grasses and wildflowers for water and nutrients, and consequently cannot survive without a suitable host such as hairy grama or June grass in the planting area. Grow it in full sun on dry, infertile, sandy or rocky soil and sow seed directly with a host plant already in place — transplanting established plants almost always fails. As a secondary selenium accumulator in high-selenium soils, it can concentrate the element in its tissues and is considered mildly toxic to pets.

Cold limit: USDA 3-8 · RHS H7 (-40 to 32 °C)

What downy painted cup's hardiness rating actually means

Yes — downy painted cup is genuinely cold hardy. Rated RHS H7 and USDA 3-8, 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 3-8 — 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. Downy Painted Cup is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for downy painted cup 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 downy painted cup go outside or overwinter — and where?

Plant it out within USDA 3-8 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 downy painted cup can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Downy Painted Cup hardiness — frequently asked questions

Is downy painted cup cold hardy?

Yes — downy painted cup is genuinely cold hardy. Rated RHS H7 and USDA 3-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Downy Painted Cup is hardy across USDA 3-8; 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 downy painted cup can survive?

Minimum survivable temperature is roughly below about −20 °C. Downy Painted Cup is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is downy painted cup?

Downy Painted Cup is rated USDA 3-8 and RHS H7 — Hardy in the severest European continental winters.

Can downy painted cup survive winter outside?

Plant it out within USDA 3-8 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 downy painted cup 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.