Alocasia care: light, water and winter dormancy

Light

Bright light that never lands directly on the leaves is what an alocasia wants. The RHS recommends bright, indirect light and warns that strong sun scorches the foliage, while NC State lists dappled or partial shade as its natural exposure. In a home, that means a spot right in front of an east window, a few feet back from a west one, or behind a sheer curtain on a south exposure; the University of Illinois Extension rates such positions at roughly 150 to 300 foot-candles.

The plant survives in dimmer rooms, but the RHS notes that growth becomes much slower, and each new leaf tends to be smaller, carried on a longer, weaker stalk that leans toward the glass. Turn the pot slightly every time you water; the RHS suggests this to stop a tall plant from becoming lopsided and unstable.

Water

From April to October, the RHS advice is to water whenever the top 2 inches (5 cm) of compost have dried. Push a finger in to the second knuckle: the surface should feel dry while the lower part of the pot is still faintly cool. Water slowly until it drains, then empty the cachepot, because the fleshy rhizome rots in compost that stays sodden. A pot that dries within a day or two of a soaking usually means roots have filled it, which the RHS treats as a cue to move up a size.

Winter changes the rules. As days shorten, many alocasias drop a few leaves and stop producing new ones; the RHS calls this dormancy and says to reduce watering to a minimum, because wet compost around a resting plant is the classic route to root rot. Give just enough water to keep the rhizome from shriveling, keep the plant above 50°F (10°C), and return to normal watering when a new leaf spears up in spring. A plant that has lost every leaf is not necessarily dead: press the base, and if it feels firm, leave it alone.

Soil and pH

The RHS mix is three parts peat-free houseplant or multipurpose compost to one part horticultural grit, which keeps water moving past the rhizome while holding enough moisture for leaves this large. NC State describes the ideal outdoor soil as slightly acidic, moist, well drained and rich in humus, so avoid lime and heavy garden soil. Tall species such as Alocasia macrorrhizos become top-heavy, and the RHS recommends a heavy terracotta pot to keep them upright. Whatever the container, it needs a drainage hole.

Humidity

Alocasias come from forests where the air rarely dries out, and the RHS links low humidity to browning leaf edges and to red spider mites, which multiply in a dry atmosphere. Heated homes fall well short in winter: the University of Illinois Extension puts most of them below 30 percent humidity. A tray of gravel or clay granules kept wet just below the surface, a humidifier, or a spot in a bright bathroom all help. Grouping plants raises the moisture around them too, and it lasts longer than misting, which Illinois says lifts humidity only briefly.

Temperature

NC State gives an ideal daytime range of 68 to 77°F (20 to 25°C), and both NC State and the RHS set 60°F (16°C) as the floor during active growth. In winter the RHS allows cooler conditions so the plant can rest, but never below 50°F (10°C). Cold drafts do as much harm as low readings: a plant beside a door that opens onto winter air, or with leaves pressed against cold glass, can lose foliage overnight. Outdoors, UF/IFAS notes that frost kills the leaves but the plant regrows from its base in USDA zone 8A and warmer; farther north, NC State suggests lifting the tubers and storing them cool and dry.

Fertilizer

Leaves that can reach 36 inches long need fuel. The RHS recommends a general liquid fertilizer from April to October at the dose and frequency on the label, and the University of Illinois Extension's general rule for houseplants is no more than once every one to three months between March and September, with a balanced or 1:2:1 formula. A fast-growing alocasia in a bright window sits at the frequent end of that range; one in modest light needs less. Stop entirely once the plant slows for winter, and flush the pot with plain water every four to six months, as Illinois advises, to clear accumulated salts.

Work out the dose for your watering can with the fertilizer dilution calculator →

Repotting

According to the RHS, an alocasia can usually stay in its nursery pot for a year or so, then needs repotting every couple of years, more often for vigorous species. Roots crowding the pot, compost that dries within days, or offsets bunched against the rim all say it is time. Repot in spring as growth resumes, into a pot only about 2 inches (5 cm) wider, with the top of the root ball just below the surface. Overpotting surrounds the rhizome with wet compost it cannot use. Wear gloves, since the sap irritates skin.

• Roots crowd the pot or circle the bottom
• The compost dries out very fast after a thorough watering
• Offsets press against the rim of the pot

Propagation

Alocasias multiply underground. Mature plants send up offsets around their base, and the RHS calls separating these in spring the easiest method: slice down with a clean knife, keep as much root as possible with each young plant, and pot it on its own in gritty compost. The fleshy rhizome can also be cut into pieces in late spring or early summer, provided each piece has a growing point; NC State lists division of offsets as the recommended strategy. Keep new divisions warm and bright, and water sparingly until fresh leaves appear. Gardeners who grow alocasias outdoors in summer can also lift the tubers in fall and start them again in pots the next year.

Methods: Separating offsets from the base of the parent, Dividing the fleshy rhizome · Best season: spring to early summer.

Common problems

Yellow leaves are hard to read on an alocasia because NC State lists three possible causes: overwatering, too little water and inadequate light. Check the compost and the calendar before acting. One old leaf yellowing while a new one opens is normal turnover, and several leaves fading in late fall usually mean dormancy. Spider mites are the pest to watch, especially in dry rooms, followed by aphids and mealybugs. Root rot and bacterial stem rot, which NC State attributes to overwatering, show as a soft, dark base.

Not sure which one it is? Try the plant problem diagnosis tool →

Is the alocasia toxic to cats and dogs?

The ASPCA lists Alocasia, all species, also called elephant's ear, as toxic to dogs, cats and horses. The toxic principle is insoluble calcium oxalates, needle-shaped crystals released when a leaf is chewed, and the clinical signs are oral irritation, pain and swelling of the mouth, tongue and lips, excessive drooling, vomiting and difficulty swallowing. NC State rates the genus as medium severity for people, with skin and eye irritation from the sap, and the RHS advises gloves. NC State notes that the corm and stem are eaten in some cuisines only after thorough cooking destroys the crystals; a raw leaf is never safe. Keep the plant away from pets and small children, and call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435 if an animal chews one.

Check any other plant against the ASPCA lists →