Cold hardiness & minimum temperature

Is Signet marigold (Tagetes tenuifolia)cold hardy? Hardiness zone & min temp

Also called signet marigold, lemon marigold, striped Mexican marigold.

More about signet marigold

About Signet marigold

Tagetes tenuifolia · also called signet marigold, lemon marigold · flowering

A delicate-looking annual with finely divided, lacy foliage and masses of small, single flowers in lemon, gold, and orange from summer to frost. Unlike other marigolds, its flowers and leaves are edible, with a pleasant citrusy tang. Heat- and drought-tolerant, it is excellent for edging, containers, and herb gardens where its fine texture contrasts well with bolder plants.

Cold limit: USDA 2-11 · RHS H1c (15–32°C)

Watch for — Fading / cessation of bloom in extreme heat: Flowers may pause during prolonged heat above 35°C. Resume as temperatures drop; light deadheading and a moderate watering encourages a fresh flush of blooms in late summer.

What signet marigold's hardiness rating actually means

Signet marigold 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 2-11 — 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 5 °C (and never frost). Signet marigold has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for signet marigold 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 signet marigold 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 signet marigold can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Signet marigold hardiness — frequently asked questions

Is signet marigold cold hardy?

Signet marigold 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. Signet marigold can only live outside year-round in genuinely frost-free climates (roughly USDA 2-11); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature signet marigold can survive?

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

What hardiness zone is signet marigold?

Signet marigold is rated USDA 2-11 and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can signet marigold 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 signet marigold 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.