Cold hardiness & minimum temperature

Is Key lime (Citrus aurantifolia)cold hardy? Hardiness zone & min temp

Also called Key lime, Mexican lime, West Indian lime, Bartender's lime.

More about key lime

About Key lime

Citrus aurantifolia · also called Key lime, Mexican lime · edible

Key lime is a small, thorny citrus producing aromatic, thin-skinned limes with intensely tart juice and a distinctive floral aroma. More frost-sensitive than Persian lime, it thrives in tropical and subtropical climates or sheltered containers. The highly fragrant foliage and rind contain citrus oils toxic to pets.

Cold limit: USDA 10-12 · RHS H1b (13-35°C)

Watch for — Frost damage: Key lime is the most cold-sensitive common citrus. Even a brief dip below 2°C can kill new growth and cause significant dieback. Bring containerised plants indoors as soon as temperatures drop in autumn.

What key lime's hardiness rating actually means

Key lime is a tender fruiting plant, not a hardy one. It crops outdoors only in roughly USDA 10-12; in cooler zones it is a container plant moved under cover for winter. Its RHS rating of H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA 10-12 — 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 10 °C (sustained cold below this is damaging). Key lime fruits in warmth and is set back or killed by frost.

Concretely, for key lime as it gets too cold:

Below about 10 °C the foliage and any fruit are damaged; a hard frost can kill the whole plant.
A light frost typically scorches leaves and ruins the current crop even when the framework survives.
Roots in a container freeze far faster than roots in the ground, so potted specimens need earlier protection.

Can key lime go outside or overwinter — and where?

It can stay outdoors year-round only in USDA 10-12; in a UK or cold-US climate it is a conservatory or move-it-indoors plant for winter.
Summer it outside in full sun for the best crop, then bring it into a cool, bright, frost-free room before the first frost.
A bright unheated (but frost-free) glasshouse or porch is the ideal overwintering spot — cool and dormant, never freezing.

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 key lime can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Frost protection for borderline key lime

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

Move containers into a frost-free glasshouse, porch or cool room before the first forecast frost.
For borderline-zone ground plants, wrap the trunk and fleece the canopy, and mulch the root zone heavily.
Keep it on the dry side over winter — cold plus wet roots is what actually kills tender fruit.

Key lime hardiness — frequently asked questions

Is key lime cold hardy?

Key lime is a tender fruiting plant, not a hardy one. It crops outdoors only in roughly USDA 10-12; in cooler zones it is a container plant moved under cover for winter. Frost-tender. Grow key lime in the ground only within USDA 10-12; everywhere colder it lives in a large pot that comes into a frost-free space each winter.

What is the minimum temperature key lime can survive?

Minimum survivable temperature is roughly about 10 °C (sustained cold below this is damaging). Key lime fruits in warmth and is set back or killed by frost.

What hardiness zone is key lime?

Key lime is rated USDA 10-12 and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can key lime survive winter outside?

It can stay outdoors year-round only in USDA 10-12; in a UK or cold-US climate it is a conservatory or move-it-indoors plant for winter. Summer it outside in full sun for the best crop, then bring it into a cool, bright, frost-free room before the first frost. A bright unheated (but frost-free) glasshouse or porch is the ideal overwintering spot — cool and dormant, never freezing.

How do I protect key lime from frost?

Move containers into a frost-free glasshouse, porch or cool room before the first forecast frost. For borderline-zone ground plants, wrap the trunk and fleece the canopy, and mulch the root zone heavily. Keep it on the dry side over winter — cold plus wet roots is what actually kills tender fruit.