Cold hardiness & minimum temperature

Is Coreopsis 'Sunray' (Coreopsis grandiflora 'Sunray')cold hardy? Hardiness zone & min temp

Also called Sunray Tickseed, Bigflower Coreopsis 'Sunray', Large-flowered Coreopsis.

More about coreopsis 'sunray'

About Coreopsis 'Sunray'

Coreopsis grandiflora 'Sunray' · also called Sunray Tickseed, Bigflower Coreopsis 'Sunray' · flowering

Coreopsis grandiflora 'Sunray' is a vibrant perennial or short-lived perennial grown for its large, deep-golden double daisy flowers that bloom prolifically from late spring into summer. It is best in full sun and well-drained soil, tolerating heat and some drought. ASPCA lists Coreopsis as non-toxic to pets.

Cold limit: USDA 4-9 · RHS H5 (-10-32°C)

Watch for — Short-lived perennial die-back: C. grandiflora can behave as a short-lived perennial in colder climates. Deadhead consistently and divide every 2-3 years to prolong the plant's life.

What coreopsis 'sunray''s hardiness rating actually means

Yes — coreopsis 'sunray' is genuinely cold hardy. Rated RHS H5 and USDA 4-9, 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 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 −15 to −10 °C. Coreopsis 'Sunray' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for coreopsis 'sunray' 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 coreopsis 'sunray' 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 coreopsis 'sunray' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Coreopsis 'Sunray' hardiness — frequently asked questions

Is coreopsis 'sunray' cold hardy?

Yes — coreopsis 'sunray' is genuinely cold hardy. Rated RHS H5 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Coreopsis 'Sunray' 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 coreopsis 'sunray' can survive?

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

What hardiness zone is coreopsis 'sunray'?

Coreopsis 'Sunray' is rated USDA 4-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can coreopsis 'sunray' 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 coreopsis 'sunray' 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.