Alocasia

The fruiting head

After pollen release the upper spadix and the spathe limb wither and fall, and only the lower spathe and the female zone go on. Each fertilized ovary becomes a berry, and the berries, packed as tightly as the pistils were, form the infructescence. The ovary holds several ovules on a basal placenta, in one chamber or partly divided above, and not all of them become seed: Shaw counted 0–10 ovules to an ovary in Alocasia brisbanensis, and in Vanuatu, Quero García and colleagues found none to four seeds in a berry of Alocasia macrorrhizos. An infructescence on an old, large wild plant usually carries more than a hundred berries, and their best hand-pollinated heads gave up to 236 seeds, ready to harvest 9–11 weeks after the cross. A head can also swell without seed: Shaw found that unfertilized florets beside real berries in Alocasia brisbanensis enlarge and deepen in color while staying empty.

Color and opening

Hay describes the fruits as orange to red, fleshy and, as far as is known, odorless. Most ripen in the orange range, Alocasia macrorrhizos, Alocasia zebrina, Alocasia reversa and Alocasia cucullata among them; Alocasia odora, Alocasia portei and Alocasia lauterbachiana ripen red; and Alocasia scalprum ripens pale cream and Alocasia azlanii white. In most species the lower spathe stays wrapped around the head as it ripens and then splits and bends back to expose the berries; in Alocasia puncakborneensis, Wong and Boyce describe it splitting lengthwise into about three segments that stay erect around scarlet berries, the peduncle doubling in length in fruit. In many species a hole opens at the apex first, as the tip of the spadix axis decays; in Alocasia macrorrhizos the axis persists and the head stays sealed until it splits.

Who eats them

Birds do. In Queensland, Shaw, Hiller and Hiller watched a Regent Bowerbird swallow 20 berries from two heads of Alocasia brisbanensis and a Lewin’s Honeyeater return to the same heads, which were empty two days later; ten people who smelled the berries found them odorless, as Hay expected of a fruit for birds. Inside the head, meanwhile, the larvae of the pollinating flies develop in the secretion that bathes it, then pupate between the fruits, and in Sabah the adults emerge together when the head splits.

The seed

The seed holds an embryo and endosperm inside its coat. Boyce gives germination in two to three weeks at 21–29 °C (70–84 °F), with the seed kept in the berry until sowing, cleaned of all pulp and covered no deeper than its own size, and he warns that metallic copper fungicides are fatal to aroid seedlings. Sowing fresh is the usual advice, but the one controlled trial points elsewhere: Abdulhafiz and colleagues found seed of Alocasia longiloba still 89% viable after two weeks of drying at room temperature, germinating at 25% in about 30 days untreated and 87.5% in 19 days after 15 minutes in 30% sulfuric acid, which they read as a hard seed coat rather than an intolerance of drying. The fruit is not to be eaten. In Sri Lanka in 1993, Goonasekera and colleagues reported two children who died after eating the ripe orange fruit of Alocasia cucullata; the cause was never identified.

The published schedules are more cautious. Bown feeds every two to three weeks, and the RHS gives a general liquid fertilizer from April to October only, at the rate on the pack. Both stop with the season, and a dormant plant, with no leaves to use it, is not fed at all. In dry air feed more lightly still, as the humidity note on the Growing Conditions tab explains.

Temperature

The RHS sets the same floor: above 16°C (60°F) through the growing season, and never below 10°C (50°F). Bown found many species going dormant below 7°C (45°F), and a grower called Dan reported on Aroid-L on May 25th, 2001, that two or three weeks of nights in the low 50s°F in the San Francisco Bay area sent most of his plants dormant, some to become leafless, slowly decaying rhizomes.

Humidity

The RHS ties browning leaf edges, and red spider mite, to dry air.

Watering

Cold is when water does harm: Denis of Silver Krome Gardens in Florida wrote on Aroid-L on July 12th, 2005, that stem rot is avoided by keeping excess water off in the rainy season and above all in the cool winter, when the plants are not growing, and the RHS names overwatering in winter, and while dormant, as the cause of root rot.

Light

Alocasia robusta is a reported exception: Peter Boyce wrote on Aroid-L on July 15th, 2009, that in cultivation it needs nearly full sun or very light shade, as befits a giant of canopy gaps.

Potting

The RHS likewise moves up only about 5 cm (2 inches) in diameter at a time, and Boyce warns against burying the base of the stem, which invariably leads to fungal or bacterial rot. For the species whose rhizome walks upward, Boyce described on Aroid-L on November 22nd, 2006, a system that keeps the new rhizome rooted: plant low in a deep pot, leaving about 15 cm (5 inches) free above the mix, top-dress with loose mix as the rhizome rises, and repot once the mix reaches the rim. Alocasia robusta is a reported exception to this rule: Peter Boyce wrote on Aroid-L on July 15th, 2009, that it is not easy and invariably reacts very badly to transplanting, and that the only way found to grow it successfully was to plant ex vitro plants directly into the final-size pot, or to sow three or four seeds directly into the final-size pot or final growing place.

Induced, not obligate

Nothing in the genus requires a rest. What brings one on is cold or drought: Bown found many species going dormant below about 7°C (45°F), and the Growing Conditions tab has a grower’s plants going dormant after weeks of nights in the low 50s°F. In a cool home the RHS expects the same each winter: in cooler, drier conditions, still above 10°C (50°F), the plant may lose some foliage, which is nothing to worry about, and fresh leaves appear when growth resumes in spring. Kept warm and moist the year round, the plants simply go on growing. Some growers find a plant resting for no reason they can name: Neal R. Foster wrote on Aroid-L on April 3rd, 1997, that his sometimes sulked and went dormant with no pattern he could find, the oldest outer leaves drooping first, and advised patience, less water and waiting for the sprouts.

Telling rest from rot

The difference is in the storage organ. A resting plant keeps a firm corm or rhizome with a live bud, however bare it looks above ground; a dying one goes soft, collapses or smells, usually from the base, and the rot spreads. If the leaves have gone, press the corm or rhizome gently at the soil line, or lift it and look. A sudden collapse of a plant in full leaf, with a mushy stem at ground level, is not dormancy but the bacterial rot described on the Pests & Diseases tab, and even then Denis of Silver Krome Gardens advised on Aroid-L on July 12th, 2005, not to throw the plant out at once, since small satellite rhizomes separated from the main stem may still regrow.

Care while resting

Keep the plant warm, never below 50°F (10°C), in its pot, and water only enough to keep the substrate from drying out completely; do not feed it. The RHS reduces watering to a minimum and names overwatering while dormant as the cause of root rot, and a grower called Russ wrote on Aroid-L on November 21st, 1999, that larger plants that had dropped to a bulb after a chill needed drier conditions, because the tubers rot if they are kept too damp. When the new shoot shows, return the plant to warmth, light and its normal watering and feeding.

Out of the ground

Corms and rhizomes are not kept out of the ground for long, but they tolerate a spell without leaves or roots, which is how they are shipped. Pot them on arrival, warm and lightly moist, as for the cormels on the Propagation tab.

Offsets, cormels and division

The RHS separates offsets with as much root as possible in spring, and Lecoufle divided rhizomes at the end of the rest season and recovered the bulblets from the old compost at repotting. Marek wrote on Aroid-L on April 8th, 2011, that the bulblets of Alocasia infernalis, about 5–10 mm (0.2–0.4 inch), generally began growth within weeks when potted and watered immediately after detachment, provided they had not dried, and that plants raised from them in his cultivation then grew slowly, with one or two leaves a year. Older offsets can sit for months: Michael Pascall wrote there on April 11th, 2011, that an old offset may have a tough skin that should be carefully broken, not removed, to make it sprout. One grower’s account shows how much a single plant can multiply: Steve Lucas wrote on Aroid-L on April 2nd, 2009, that a single small Alocasia odora he was given in 1996 multiplied until plants had to be dug up and discarded every summer, with about ten large plants given away the previous summer and as many discarded. In his experience they grow like weeds if kept humid and somewhat damp.

Tissue culture

Tissue culture rescued Alocasia scabriuscula var. imperialis (published as Alocasia guttata) when it was known from a single collection. Hyndman cautions that micropropagated plants are free of a disease only if tested for that pathogen, and that variation arising in culture is more likely to be worse than the parent than better. Abdulhafiz and colleagues published a full route for Alocasia longiloba, with 97% of plantlets surviving acclimatization.

Seed and hybrids

Alistair Hay wrote on Aroid-L on April 1st, 1999, that the genus hybridizes freely in cultivation and occasionally in the wild, even between distantly related species, and that some hybrids are fertile; in Vanuatu, Quero García and colleagues found wild Alocasia macrorrhizos largely self-incompatible, setting no fruit from 20 single self-pollinations but fruit from 79 of 88 outcrosses. Seedlings of such hybrids can vary widely: Ron Weeks wrote on Aroid-L on April 3rd, 2000, that the many Alocasia ‘Portora’ and Alocasia ‘Calidora’ seedlings he bought and grew out ranged from lance-leaved miniatures to broad-leaved giants. With the help of Jim Georgusis he selected a red and a green form of Alocasia ‘Portora’ and one form of Alocasia ‘Calidora’ for tissue-culture production, and the green form was dropped from that production because landscapers either preferred the red form or did not care. The interactive dashboard at the bottom of this page lists every known hybrid.

Other pests

Mealybugs turn up too, and outdoors in Florida scale can recur: Debbie Swartz described on Aroid-L on October 1st, 2000, a black scale on outdoor plants in Fort Lauderdale. The EPPO database records the thrips Chaetanaphothrips signipennis on Alocasia ×amazonica. And in North Carolina, Petra wrote on Aroid-L on October 30th, 2002, that a shiny black caterpillar eating out the core of a stem was identified as the larva of a Bellura moth, a borer that had been found on other aroids.

Rots of the corm, rhizome and roots

Root rot from overwatering, particularly in winter, is the one disease the RHS names. Bacterial soft rot is the fastest. Denis of Silver Krome Gardens wrote on Aroid-L on July 12th, 2005, that Alocasia, particularly the ‘Amazonica’ types, are prone to bacterial infection, usually Erwinia, at the base of the rhizome; a plant can show nothing until it falls over on a mushy stem at ground level, and more fungicide did not solve it in his experience. The bacteria once called Erwinia chrysanthemi are now Dickeya, and Nelson’s University of Hawaiʻi fact sheet lists Alocasia among the interior plants it commonly affects: it rots fleshy organs, leaves, roots, tubers and stems, can run through the plant’s vessels, and gives a mushy, foul-smelling rot. Sprays do little against it. The defense is cultural: clean stock, new or sterilized pots and mix, no overhead watering, which splashes the bacteria from leaf to leaf and plant to plant, removal and destruction of infected plants, and avoiding the stresses of irregular watering, poor drainage, fluctuating temperatures and pots too small or too large. In 2025, Marin and colleagues reported the southern blight fungus, Agroathelia rolfsii, for the first time on Alocasia, in a Florida field of ‘Calidora’ with about 10% of plants stunted and yellowing, their bulbs rotting under white mycelium and sclerotia; the field had grown caladiums before, and the sclerotia persist in soil for years.

Virus

Dasheen mosaic virus infects aroids widely, Alocasia among them: Greber and Shaw found it in wild and cultivated plants in coastal Queensland, and Zettler and Hartman list Alocasia among the cultivated aroids it infects. It is spread by aphids and in sap on cutting tools and is carried into offsets, so infected stock cannot give clean divisions; tissue culture from tested stock is the control, and has been used commercially since about 1980.

Handle with care

The tissues carry raphides, bundles of needle-shaped calcium oxalate crystals, which Osuji and Ihenko found in cells along the latex vessels of Alocasia macrorrhizos. The RHS advises gloves when handling, since the sap can irritate the skin, and in Japan, Yanagawa and Nagasawa reported five suspected cases of poisoning by Alocasia odora eaten in mistake for edible plants. Keep plants, and above all the orange fruit, out of reach of children and pets.