Cold hardiness & minimum temperature

Is Water Spinach 'Pak Boong' (Ipomoea aquatica 'Pak Boong')cold hardy? Hardiness zone & min temp

Also called pak boong, Thai water spinach, swamp morning glory.

More about water spinach 'pak boong'

About Water Spinach 'Pak Boong'

Ipomoea aquatica 'Pak Boong' · also called pak boong, Thai water spinach · edible

'Pak Boong' is the classic Thai water spinach, a slender-leaved kangkong grown for its crisp hollow stems and tender tips used in stir-fries. A heat-loving semi-aquatic vine, it grows explosively in warm, wet conditions, cropping within 4-6 weeks and regrowing after each cut for repeated harvests right through summer.

Cold limit: USDA 10-12 (frost-tender; grown as a warm-season annual elsewhere) · RHS H1c (needs heat; grown under glass or as a summer annual in the UK) (24-35°C)

Watch for — Frost and cold: Stops growing in cool weather and dies at the first frost. Restrict to warm spells, a greenhouse, or a heated indoor setup.

What water spinach 'pak boong''s hardiness rating actually means

Water Spinach 'Pak Boong' is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 10-12 (frost-tender; grown as a warm-season annual elsewhere) — 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 5 °C (and never frost). Water Spinach 'Pak Boong' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for water spinach 'pak boong' as it gets too cold:

Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can water spinach 'pak boong' go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 water spinach 'pak boong' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Water Spinach 'Pak Boong' hardiness — frequently asked questions

Is water spinach 'pak boong' cold hardy?

Water Spinach 'Pak Boong' is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Water Spinach 'Pak Boong' can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12 (frost-tender; grown as a warm-season annual elsewhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature water spinach 'pak boong' can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Water Spinach 'Pak Boong' has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is water spinach 'pak boong'?

Water Spinach 'Pak Boong' is rated USDA 10-12 (frost-tender; grown as a warm-season annual elsewhere) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can water spinach 'pak boong' survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to water spinach 'pak boong' below its minimum temperature?

Below about about 5 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.