Cold hardiness & minimum temperature

Is Finger Lime (Microcitrus australasica)cold hardy? Hardiness zone & min temp

Also called finger lime, Australian finger lime, citrus caviar.

More about finger lime

About Finger Lime

Microcitrus australasica · also called finger lime, Australian finger lime · edible

The Australian finger lime is a thorny rainforest citrus prized for its caviar-like vesicle pearls that burst with tart juice. Slow-growing and frost-tender, it thrives in a sheltered, sunny spot or a large container moved indoors over winter. Expect fruit from late autumn, with cultivars ranging from green to crimson pulp.

Cold limit: USDA 9-11 (container/overwinter indoors in cooler zones) · RHS H2 (10-30°C)

Watch for — Spider mites: Thrive on dry, dusty foliage indoors and over winter; check leaf undersides for stippling and fine webbing and raise humidity.

What finger lime's hardiness rating actually means

Finger Lime is a tender fruiting plant, not a hardy one. It crops outdoors only in roughly USDA 9-11 (container/overwinter indoors in cooler zones); in cooler zones it is a container plant moved under cover for winter. 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 (container/overwinter indoors in cooler 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. Finger Lime fruits in warmth and is set back or killed by frost.

Concretely, for finger lime as it gets too cold:

Below about 1 to 5 °C — tolerates cold but no real frost 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 finger lime go outside or overwinter — and where?

It can stay outdoors year-round only in USDA 9-11 (container/overwinter indoors in cooler zones); 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 finger lime 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 finger lime

Finger 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.

Finger Lime hardiness — frequently asked questions

Is finger lime cold hardy?

Finger Lime is a tender fruiting plant, not a hardy one. It crops outdoors only in roughly USDA 9-11 (container/overwinter indoors in cooler zones); in cooler zones it is a container plant moved under cover for winter. Frost-tender. Grow finger lime in the ground only within USDA 9-11 (container/overwinter indoors in cooler zones); everywhere colder it lives in a large pot that comes into a frost-free space each winter.

What is the minimum temperature finger lime can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Finger Lime fruits in warmth and is set back or killed by frost.

What hardiness zone is finger lime?

Finger Lime is rated USDA 9-11 (container/overwinter indoors in cooler zones) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can finger lime survive winter outside?

It can stay outdoors year-round only in USDA 9-11 (container/overwinter indoors in cooler zones); 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 finger 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.