|Classified:||(L.) G.Don, 1846|
|Propagation:||From From division, seeds, bulbils|
|Watering:||Keep the soil slightly moist but not wet|
|Fertilization:||Monthly during active growth|
|Humidity:||High humidity preferred, low humidity tolerated|
|See more Alocasia|
Giant Taro, Alocasia metallica, Alocasia plumbea, Alocasia grandis, Alocasia marginata
Alocasia macrorrhizos is a flowering plant of the Araceae family, typically grown for its distinctive 'elephant ear' foliage. Native to East Asia, it makes an excellent houseplant and will tolerate a wide range of growing conditions.
Alocasia comes from the Greek 'a' meaning without and 'Colocasia' the name of a closely allied genus, from which it was separated.
Macrorrhizos is from the green 'macros' meaning 'large' and 'rhizos' meaning 'root'.
A. macrorrhizos has beautiful green shiny leaves with light green undersides. The leaves are held on green petioles from a woody base. The leaves can grow up to 90cm in length in a mature specimen.
These leaves emerge from an underground corm. A corm is the swollen base of a stem axis enclosed by dry scale-like leaves that form a protective shell.
The A. macrorrhizos inflorescence consists of an erect spadix enclosed in a green, boat-shaped spathe. The corn-like spadix is covered in small flowers.
A. macrorrhizos likes a bright aspect with lots of sun: directly in an east or west facing window or bright dappled shade outdoors.
Use a well draining soil mix (see aroid soil), amended with more moisture retentive potting mix than for most Aroids and water thoroughly, allowing excess to drain. Alocasia do like more constant moisture than most Aroids but a waterlogged soil will lead to root rot.
Alocasia are unusually sensitive to low temperatures in the home. In winter with low light and low temperatures near windows they can enter a dormancy, so it is best to avoid placing them in an unheated room or near to a cold window. Dormancy will involve the plant dropping all its leaves and existing as an underground corm. If you push your finger down into the soil and feel the underground corm it should feel firm and not squishy. If the plant enters dormancy happens you can force the plant out of dormancy. This is a similar process to propagating Alocasia from a bulbil.
Dropping leaves after bringing the plant home
Alocasia are a temperamental genus of plants. Moving them from the hot, humid and ideal conditions of a nursery to your dim and dry home can be stressful, and the plant will respond by dropping old leaves to preserve resources. After a few weeks the plant should stabilise at between three and five leaves at any one time.
Unlike many other plants, yellowing and dying leaves on Alocasia isn't a sure sign that there are issues. Alocasia only hold a certain number of leaves at any one time, dependent on the health and size of the root system.
If your A. macrorrhizos produces a new leaf at the same time as losing the oldest or outmost leaf on the corm then this is natural and nothing to worry about.
If the soil is staying moist for more than two weeks between watering, or the soil feels soggy or very wet after a week then consider repotting the plant into a smaller container: the roots staying wet for too long will lead to root rot and a quick decline in the plant's health. When repotting use a mix that drains well but retains some moisture (see aroid soil)
A. macrorrhizos can take some direct sun without damage but requires acclimatisation first or leaves will become bleached, will turn brown and eventually die. When moving your plant into an area which gets direct sunlight build up the plant's tolerance first. Limit the amount of direct sun to an hour a day for a few days, then two hours, then three and continue to slowly increase the plant's light exposure until it is fully acclimated.
When moving the plant outdoors, choose a spot in shade or that gets dappled or screened sunlight. Let the plant slowly acclimate to being outdoors and never move the plant into direct sun without slowly building up a tolerance first. Some direct morning or evening sun is fine but hot midday light will scorch the leaves.
If your Alocasia drops all its leaves it may be a sign it has entered dormancy. This is a natural way the plants can cope with colder winter weather. Unlike Caladium this dormancy is not seasonal and can be avoided by keeping the plant somewhere warm (above 15C/60F) throughout the coldest months of the year.
To test that the plant has entered dormancy and hasn't just died, push your finger down into the soil and feel the underground corm, which should be firm and not squishy or rotten.
To bring the plant out of dormancy take the plant pot and place it in a sealed plastic bag. Put this bag somewhere relatively hot within your home - an airing cupboard or on top of a book on a radiator. Make sure to check the soil every other day and keep it slightly moist around the corm and air out the bag, removing any condensation to avoid rot. After around two weeks you should see a new leaf bud appearing at the top of the corm and at that point you are safe to move the plant back to its place within your home.
A. macrorrhizos can be affected by spider mites, mealybugs, scale, thrips and whitefly.