Citrus australasica (Finger Lime)

Australian Finger Lime (Citrus australasica): A Gourmet Citrus Marvel

The finger lime tree (Citrus australasica), also known as Australian finger lime or caviar lime, is a unique citrus native to the subtropical rainforests of Queensland and New South Wales, Australia. Famous for its elongated, gherkin-like fruit and vibrant, pearl-like juice vesicles, the finger lime citrus has become a sought-after delicacy in gourmet cuisine worldwide. Beyond its culinary charm, this thorny, spiny shrub or small tree has remarkable resilience to pests and diseases, including citrus greening, making it a valuable asset to citrus breeding programs.

The finger lime belongs to the citrus family Rutaceae, which includes other popular citrus fruits such as grapefruit, orange, lemon, pomelo, clementine, mandarin, tangerine, kumquat, calamansi, Key lime, and Kaffir lime.

What is a Finger Lime?

Description

The finger lime is a small, thorny shrub or tree that can reach up to 33 feet (10 m) in the wild but is often maintained at much smaller sizes in cultivation. It produces cylindrical fruits 2–3 inches (5–8 cm) long, with tapered ends and a rough, pebbled rind. Colors vary dramatically—from green and yellow to pink and red—while the interior is filled with juice vesicles that resemble citrus caviar. These vesicles pop in the mouth with a bright, tart flavor often likened to a mix of lime, grapefruit, and lemon.

Native Range

Citrus australasica is native to the lowland rainforests and open woodlands of southeastern Queensland and northeastern New South Wales, Australia. It thrives in disturbed, basalt-rich soils and has long been part of Aboriginal diets and traditional medicine.

Growth Habit

The Australian finger lime grows as a thorny, dense understorey shrub or small tree. It features sharp 2.5 cm (1 in) spines along the leaf axils and small, obovate to rhombic leaves about 1–2.5 cm long. The plant forms a bushy, upright habit and tolerates pruning well.

Size

In cultivation, finger lime trees typically reach 6–12 feet (1.8–3.6 meters) tall and 4–8 feet (1.2–2.4 meters) wide. Their compact size makes them suitable for container gardening or small backyard orchards.

Flowers

The plant produces small, fragrant white flowers with 20–25 stamens, appearing singly or in pairs. Petals are about 9 mm (0.35 in) long, often with a hint of pink. These flowers attract native pollinators and herald fruit development.

Blooming Season

Blooming typically occurs from late spring through early summer, with fruit ready for harvest 5–7 months later. In warm climates, the tree may flower multiple times annually.

Fruits

The fruit is a cylindrical berry, 2–4 inches (5–10 cm) long, with rough skin and a wide range of rind and pulp colors. Inside, the fruit contains spherical vesicles—”citrus caviar”—that burst with tangy, aromatic juice. Color combinations include green rind with pale green pulp, red skin with pink vesicles, and more.

Leaves

Leaves are small, narrow, and light green with a glossy surface and faint scalloping near the tip. Like other citrus, they are rich in oil glands and release a strong aroma when crushed. The foliage is evergreen, dense, and attractive year-round.

Hardiness

USDA Zones 9–11. Finger limes are moderately frost-tolerant once established but prefer warm, sheltered positions. In colder regions, grow in containers and overwinter indoors.

Uses

• Culinary: Juice vesicles are used in fine dining for seafood, sushi, desserts, cocktails, and more.
• Preserves: Used in jams, pickles, marmalades, and dried spice mixes.
• Medicinal: Traditionally used by Aboriginal Australians for immune support and wound treatment.
• Breeding: Crossed with other citrus species to develop greening-resistant varieties.
• Ornamental: Attractive compact tree with gourmet appeal.
• Beyond Lemon and Orange: Citrus You’ve Never Heard Of (But Need to Taste)

Toxicity

No known toxicity to humans or pets. However, thorny branches require care when handling to avoid injury.

Finger Lime Nutrition

A 100-gram serving of finger lime (approximately 7–10 fruits) contains about 25–30 calories, 4–7g of carbohydrates, and around 3g of fiber. It delivers between 80–88mg of vitamin C—nearly 98% of the daily recommended intake—alongside trace amounts of vitamin A, vitamin E, folate, potassium, magnesium, and calcium. Composed of nearly 90% water, the fruit is exceptionally hydrating and low in fat and protein.

Antioxidants

Finger lime vesicles are rich in phenolic compounds and flavonoids, offering potent anti-inflammatory and antioxidant effects. These help neutralize free radicals and may support cellular health, cardiovascular function, and cognitive performance.

Traditional Uses

Aboriginal communities in Australia have harvested finger limes for millennia. The juice and skin were used to treat cuts and minor wounds, while the fruit served as an important source of hydration and nutrition during dry seasons.

Modern Applications

• Natural flavor enhancer in low-calorie foods and beverages
• Rich source of vitamin C for functional nutrition and supplements
• Flavoring agent in luxury cosmetics and artisanal skincare products

Finger Lime Health Benefits

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How to Grow and Care for Finger Lime Trees

Light Requirements

Finger lime trees thrive in full sun and need at least 6–8 hours of direct sunlight each day to produce fruit effectively. In cooler or marginal climates, plant them in the warmest, most sheltered spot available.

Soil Requirements

Finger lime citrus prefers well-draining, slightly acidic to neutral soil with a pH of 5.5–6.5, though it can tolerate up to 7.0. Enhance poor soils with organic compost and coarse sand or perlite to improve aeration. Avoid heavy clay soils unless amended for proper drainage.

Watering

Maintain evenly moist soil, allowing the top inch to dry out between waterings. Overwatering can cause root rot, especially in containers. Once established, finger lime trees tolerate brief dry spells but need consistent moisture during flowering and fruiting for best performance.

Fertilizing

Feed with a balanced citrus fertilizer rich in potassium every 6–8 weeks from spring through early fall. Organic citrus blends or slow-release formulations also work well. Reduce or stop fertilization during winter dormancy.

Pruning

Prune annually to maintain shape, remove dead or diseased wood, and improve air circulation. Wear protective gloves and long sleeves to protect against thorns. Pruning encourages bushier growth and can help improve fruit yield and access to inner branches.

Container Growing

Finger lime trees grow well in containers. Choose a large pot with good drainage and fill it with well-draining citrus potting mix. In cold climates, bring containers indoors before the first frost and place near a sunny window. Maintain humidity with regular misting or a humidifier, and prune as needed to control size.

How to Grow Citrus Indoors: From Fragrant Blooms to Homegrown Fruit

How to Harvest Finger Limes

When to Harvest

• Harvest season typically runs from late summer through fall (about 6–9 months after flowering).
• In the Southern Hemisphere, the peak harvest is usually from March to May.
• Exact timing varies by region and cultivar.
• Fruits are ready when:
  • They are firm and full-colored.
  • They yield slightly to gentle pressure.
  • They detach easily from the tree with little resistance.
• Color varies by variety—green, red, yellow, purple, or nearly black.
• Underripe fruit is overly tart, with pulp that doesn’t release easily.
• Some ripe fruit may naturally fall from the tree when ready.

How to Harvest

• Use thick gloves to avoid thorn injury during harvesting.
• Snip fruits off with clean pruners to avoid damaging branches.
• Harvest regularly to encourage further flowering and fruiting.

Storage

• Store fresh finger limes in the refrigerator for 2–3 weeks.
• The pulp (“citrus caviar”) can be frozen for months without losing texture or flavor.
• Avoid prolonged storage at room temperature.

How to Propagate Finger Lime

Propagation by Seeds

• Extract seeds from fully ripe fruit and plant them immediately in a moist, well-drained seed-starting mix.
• Keep seeds in a warm location (70–85°F / 21–29°C); germination may take 2–8 weeks.
• Seed-grown trees will not be true to type and often differ in fruit quality and yield.
• Seedlings may take 7–15 years to mature and bear fruit.

Propagation by Cuttings

• Take semi-hardwood cuttings in spring or early summer from healthy, non-flowering branches.
• Dip cut ends in rooting hormone and place in a humidity dome or covered tray with bright, indirect light.
• Rooting may begin within 2 weeks but often takes 6–10 weeks or longer; success rates can be low.
• Cuttings are best suited for container plants and may lack the vigor of grafted trees.

Grafting

• Graft finger lime scions onto hardy rootstocks such as trifoliate orange (Citrus trifoliata) to improve vigor and disease resistance.
• Best performed in late winter to early spring while rootstock is actively growing.
• Common techniques include chip budding and whip-and-tongue grafting.

Air Layering

• A less common but effective method for propagating finger lime while preserving parent characteristics.
• Wound a healthy branch, apply rooting hormone, and wrap with moist sphagnum moss and plastic wrap.
• Roots typically develop in 6–8 weeks, after which the branch can be severed and potted.

Common Pests and Diseases of Finger Lime

Common Pests

• Scale Insects: Attach to stems and leaf undersides, excreting honeydew that fosters sooty mold. Control with horticultural oil, insecticidal soap, or manual removal.
• Katydids: Chew on leaves and young fruit, leaving scars and deformities. Handpick or use row covers as needed.
• Caterpillars & Moth Larvae: Includes citrus leaf miners and other larvae that damage foliage. Remove manually or apply organic treatments like Bacillus thuringiensis (Bt) or spinosad.
• Whiteflies: Sap-sucking insects that cause leaf yellowing and contribute to sooty mold. Use sticky traps, neem oil, or insecticidal soap.
• Grasshoppers & Other Bugs: May chew foliage and fruit, including spined citrus bugs and bronze orange bugs. Control only when populations are high.
• Aphids: Distort new growth, secrete honeydew, and attract sooty mold. Spray with neem oil or insecticidal soap.
• Mealybugs: Cottony white insects that suck sap and weaken plants. Treat with horticultural oil or manual removal.
• Spider Mites: Cause stippling, yellowing, and leaf drop in dry conditions. Increase humidity and treat with miticides if necessary.
• Weevils: Notch leaves and damage roots. Inspect regularly and manage with sticky traps or soil treatments if needed.

Common Diseases

• Root Rot: Caused by overwatering or compacted soil. Ensure proper drainage and avoid over-irrigation.
• Citrus Greening (HLB): Finger lime shows tolerance or resistance, but monitor for signs like blotchy yellowing leaves and lopsided, bitter fruit.
• Phytophthora Root Disease: Finger lime is resistant to Phytophthora citrophthora, but well-drained soil remains essential to avoid infection.
• Sooty Mold: Fungal growth on honeydew from pests like scale, aphids, and whiteflies. Manage by controlling underlying infestations.
• Citrus Canker: Less common in finger limes, but still a risk. Look for lesions with yellow halos. Prune affected parts and apply copper-based fungicides.
• Citrus Gall Wasp, Melanose, Citrus Scab: Occasionally affect finger limes, especially in humid or poorly ventilated conditions. Remove affected branches and improve airflow.

Prevention Tips

• Plant in a well-ventilated location with good spacing between trees to promote air circulation.
• Inspect trees regularly for early signs of pests or disease.
• Clean and sterilize pruning tools between uses to prevent disease spread.
• Apply mulch to retain soil moisture, but keep it 2–3 inches away from the trunk to prevent rot.
• Use organic sprays or horticultural oils preventatively if pest activity is common in your area.