Cold hardiness & minimum temperature

Is Kumquat (Fortunella japonica)cold hardy? Hardiness zone & min temp

Also called round kumquat, Marumi kumquat.

More about kumquat

About Kumquat

Fortunella japonica · also called round kumquat, Marumi kumquat · edible

The round (Marumi) kumquat is a compact, cold-hardiest of the citrus relatives, bearing small, oval-to-round orange fruit eaten whole — sweet rind, tart flesh. Its tidy size, glossy evergreen leaves, and fragrant white blossoms make it a favorite container and ornamental fruiter. It needs full sun, sharp drainage, and citrus feeding, but tolerates more cold than lemons or limes.

Cold limit: USDA 8-11 outdoors (the most cold-tolerant of the common citrus group); container-grown and overwintered indoors in colder zones · RHS H2 (13-30°C)

Watch for — Leaf and fruit drop: Triggered by watering swings, cold drafts, or low light. Keep moisture even and the plant in a stable, bright, warm position; some natural fruit thinning is normal.

What kumquat's hardiness rating actually means

Kumquat 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 8-11 outdoors (the most cold-tolerant of the common citrus group); container-grown and overwintered indoors in colder zones — 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. Kumquat shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for kumquat 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 kumquat go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 outdoors (the most cold-tolerant of the common citrus group); container-grown and overwintered indoors in colder zones 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 kumquat 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 kumquat

Kumquat 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.

Kumquat hardiness — frequently asked questions

Is kumquat cold hardy?

Kumquat 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 8-11 outdoors (the most cold-tolerant of the common citrus group); container-grown and overwintered indoors in colder zones (and sheltered UK gardens) kumquat can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature kumquat can survive?

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

What hardiness zone is kumquat?

Kumquat is rated USDA 8-11 outdoors (the most cold-tolerant of the common citrus group); container-grown and overwintered indoors in colder zones and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can kumquat survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA 8-11 outdoors (the most cold-tolerant of the common citrus group); container-grown and overwintered indoors in colder zones 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 kumquat 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.