Alocasia

Light and exposure

The alocasia wants plenty of light, but indirect. In the wild it grows under the canopy, bathed in filtered light and never scorched by harsh sun. At home, a bright spot near an east-facing window, or slightly set back from a south-facing one, suits it well.

Direct afternoon sun quickly marks and burns its large leaves, while a spot that is too dark makes it decline, with stretched petioles and smaller leaves. In our weak winter light, move it right up to the window, or add a grow light if you want to limit leaf loss.

Watering

Keep the substrate lightly moist in spring and summer, without ever soaking it. Water as soon as the top centimetre has dried, with room-temperature water, ideally low in lime. The alocasia hates prolonged drought as much as standing water, it is a balance to find.

In winter, everything changes. The plant slows down or goes fully dormant, and its water needs collapse. Cut back sharply and let the substrate dry out much more between waterings. If the leaves fall and only the tuber remains, keep the soil barely damp, never soaked, or the resting tuber will rot.

Soil and repotting

Give it an airy, free-draining substrate that holds a little moisture without ever compacting. A mix of potting soil, fine bark and perlite, with a share of coconut fibre, closely reproduces the light forest floor it likes. A pot with drainage holes is essential.

The alocasia is happy in a fairly snug container, which warms up and dries out a little faster. Repot in spring, as growth resumes, when the roots circle the bottom. It is also the chance to inspect the tuber and spot any offsets. Avoid repotting during full winter dormancy, the plant will not settle in while it sleeps.

Temperature and humidity

Constant warmth is a condition for success. The alocasia is comfortable between 18 and 27 degrees and dislikes sudden swings. Below 15 degrees it sulks, stops growing, and the cold triggers leaf drop.

It tolerates no frost and never overwinters outside here. Avoid cold draughts, poorly insulated windows and the vicinity of a door opening outdoors in winter. Conversely, keep it a little away from radiators, which dry out the air it needs so badly. A warm, stable room, a bright bathroom for instance, often works wonders.

Pruning and upkeep

The alocasia is not pruned for shape. Simply cut off yellowed or dried leaves at the base, with a clean tool, as they fade. It is normal for an old leaf to give way when a new one unfurls, the plant only keeps a limited number of leaves at a time.

In autumn and winter, this yellowing can speed up until the foliage is fully lost. Only cut the petiole once it is soft and clearly yellow, not before: as long as it is green, it still feeds the tuber. Wear gloves for this work, as the sap is irritating.

Pests and diseases

In our climate, trouble comes mainly from too much water and air that is too dry. Overly generous watering in winter rots the roots and tuber: soft leaves, general yellowing, a smell of stale soil. The fix is to dry out, unpot to inspect the tuber and cut away the soft parts.

The dry air of our heated homes favours spider mites, which pierce the underside of the leaves and leave fine webbing. Also watch for scale insects and aphids. Good humidity, regularly wiped foliage and careful checking keep these attacks in check. Spots on the leaves often betray water that is too hard, or a root problem, rather than a real disease.

Propagation

The alocasia is propagated by dividing the tubers, not by stem or leaf cuttings. When repotting in spring, gently free the root ball: you will often find small bulbils or offsets clinging to the main tuber. Detach them with a few roots.

Plant each offset in a small pot of light substrate, keep it warm, in filtered light and a humid atmosphere, and be patient: the start is slow and temperamental. A clear cover or a mini greenhouse keeps up the humidity that helps it take. Always handle with gloves, as the sap and tubers are irritating.

Toxicity

The whole plant is toxic. Alocasias contain calcium oxalate crystals, highly irritating, present in the leaves, stems and sap. Chewed or swallowed, a leaf causes an intense burning sensation in the mouth and throat, heavy salivation, swelling of the lips and tongue, and sometimes difficulty swallowing. Contact of the sap with the skin or eyes can irritate sensitive people.

Keep the plant out of reach of young children and pets, cats and dogs in particular, which like to nibble the leaves. If swallowed, rinse the mouth, give a little to drink, and contact a doctor, the poison centre or a vet. Wear gloves when repotting or dividing, and wash your hands afterwards, especially before touching your face.

Month-by-month care calendar

Green Hub tips

• Never throw out an alocasia that has lost its leaves in winter. As long as the tuber is firm, it is simply sleeping and will start again in spring.
• Air humidity is the key to success. A bright bathroom, a group of plants or a tray of moist clay pebbles beats a dry, overheated room.
• Water by how dry the substrate is, never out of habit. Excess water, especially in winter, rots the tuber and kills more alocasias than thirst.
• The whole plant is toxic through its calcium oxalates. Keep it out of reach of children and animals, and wear gloves to prune or divide it.
• In winter, give it as much light as possible, even adding a grow lamp: this is often what makes the difference between keeping its foliage and going dormant.