Cold hardiness & minimum temperature

Is Blue dawn flower (Ipomoea indica)cold hardy? Hardiness zone & min temp

Also called Blue dawn flower, Blue morning glory, Oceanblue morning glory.

More about blue dawn flower

About Blue dawn flower

Ipomoea indica · also called Blue dawn flower, Blue morning glory · tropical

Ipomoea indica is a perennial morning glory producing an abundant succession of large, vivid blue-violet funnel flowers that open each morning from spring through autumn. Native to tropical America and now widely naturalised in warm regions worldwide, it is classified as invasive in several countries. A vigorous wall or fence plant for frost-free climates.

Cold limit: USDA 9–11 · RHS H2 (10°C to 38°C)

Watch for — Frost dieback: Top growth is killed by frost below about 2–4 °C. In marginal zones (USDA 8–9), the rootstock often survives mild winters below ground and resprouts vigorously in spring. In colder climates, treat as an annual or lift and overwinter roots frost-free.

What blue dawn flower's hardiness rating actually means

Blue dawn flower is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 9–11 — 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 1 to 5 °C — tolerates cold but no real frost. Blue dawn flower shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for blue dawn flower as it gets too cold:

Down to roughly about 1 to 5 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can blue dawn flower go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 9–11 or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 blue dawn flower can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline blue dawn flower

Blue dawn flower is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Blue dawn flower hardiness — frequently asked questions

Is blue dawn flower cold hardy?

Blue dawn flower is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA 9–11 (and sheltered UK gardens) blue dawn flower can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature blue dawn flower can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Blue dawn flower shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is blue dawn flower?

Blue dawn flower is rated USDA 9–11 and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can blue dawn flower survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 9–11 or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect blue dawn flower from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.