Amorphophallus are the giants of the aroid family, dwarfing their distant European and western Asian cousins, the Arums and Biarums. Among them is the infamous Amorphophallus titanum from western Sumatra, a species reknowned for producing the largest inflorescence of any plant.
A dwarf in comparison, Amorphophallus konjac is nevertheless an extremely impressive plant. Stunning in and out of flower, this species from China, Japan and Vietnam is probably the easiest of the genus to cultivate.
Vital Statistics
Konjac is also one of the most impressive. Amorphophallus come in all sizes, from Asian forest monsters to miniatures only a few inches high. Amorphophallus konjac resides somewhere in the middle. A mature tuber produces a single umbrella-like leaf, several feet across on a robust stem which is itself up to a metre in height.
The green stem is heavily mottled with purple blotches, while the spreading leaf is deeply dissected into roughly diamond-shaped or oval segments. The effect is extremely ornamental and, when in leaf, the plant makes an excellent container specimen for a semi-shaded, sheltered patio or courtyard.
Amorphophallus konjac In Flower
If the foliage of Amorphophallus konjac is pleasing to the eye, its inflorescence is another matter altogether. In Spring, before the leaf emerges, a large tuber sends up a powerful stem that may grow to 1.5 metres in altitude. This bears a huge, leathery spathe, mottled on the outside and luridly maroon within, while from the centre juts a vast, gnarled spadix of similar coloration.
This frightening inflorescence emits a stench of gargantuan proportions. Smells are subjective but however the distinctive "perfume" of konjac might be described, it is powerful enough to make its presence known at a distance of 10 metres and more. This high level of potency is, of course, exactly what the plant needs to attract its insect pollinators.
Cultivating Amorphophallus konjac
Would-be growers should not be put off by these dubious qualities, however. Small offset tubers are frequently available for sale and make attractive plants in their first year of growth. It may be several years before they reach flowering size but tubers weighing at least1 kilogram are likely to produce an inflorescence. By adhering to a few guidelines, cultivation should present no problems:
Compost
Konjac are hungry plants and appreciate a fertile, well drained soil containing plenty of organic matter, although they will tolerate a heavier, loam-enriched compost than other species.
Pots and Planting
Containers must be deep and at least twice the diameter of the tuber. Amorphophallus have extensive contractile roots which pull the plant deeper into the compost, and the new tuber that forms during a good growing season will be substantially bigger than the original. It will also produce offsets on the ends of radiating stolons, which require a spacious pot in which to develop if they are not to become cramped.
Plant non-flowering tubers at a good depth in April. The roots grow from the top and may emerge from the soil if the tuber is too shallow. In addition, a tuber that is not deep enough will produce an unstable plant that could easily fall over.
Mature tubers often begin to produce their flowering stem very early in the Spring and should be planted as soon as they show any sign of doing so.
Feeding and Watering Amorphophallus konjac
When the new shoot emerges - usually in May or June in the Northern Hemisphere - gradually increase the amount of water. These are large plants and they should not be allowed to dry out and wilt, but waterlogging should also be avoided.
Feed the plants once a fortnight with a high phosphate fertilizer. This will promote the development of a large tuber which will ensure bigger, healthier plants next year.
Temperature
Amorphophallus konjac can withstand lower temperatures than its tropical cousins and will cope with cooler spells down to 15º C, although for optimum performance, aim for a minimum temperature of 20º C throughout the growing season.
Positioning Your Amorphophallus konjac
Site the plants in a sheltered, windless position in dappled light. Prolonged direct sunlight or exposure to wind will scorch and tear the leaves, rendering the plants unsightly.
Dormancy
All watering ceases as the days shorten and the leaf begins to turn yellow. Once this has collapsed, the tuber should be removed from the pot, cleaned, and stored completely dry at average room temperature. Cold damp conditions must be avoided at all costs as these will inevitably cause the tubers to rot.
Propagating Amorphophallus konjac
If pollination has occurred, konjac may produce large numbers of fruit. The seeds have a short viability and must not be allowed to dry out. In the case of Amorphophallus konjac, however, it is seldom necessary to grow the plants from seeds as even small tubers produce plentiful offsets which usually detach easily from the parent plant.
The Versatile Aroid
Throughout its Asian homeland, konjac is best known for its culinary properties. It has been grown as a food crop in Japan for centuries. The tubers also contain a polysaccharide called mannan which, when bonded with glucose, produces a soluble fibre called glucomannan. This calorie-free substance is used in slimming products and to alleviate bowel problems.
Bizzare, dramatic and useful, konjac deserves a place of honour in the collection of plant enthusiasts and is sure to engender an abiding interest in that most exceptional of plant families, the aroids.
References
Deni Bown: Aroids: Plants of the Arum Family Timber Press; Oregon 2000: ISBN 0 88192 485 7
International Aroid Society: The Genus Amorphophallus
Peter Ashby - Peter Ashby lives near Granada in southern Spain, is an expert on natural history, and a dedicated traveller, writer and hispanist.
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