Amorphophallus konjac (konjak)

Japanese name: コンニャク （蒟蒻）
Scientific name: Amorphophallus konjac

[Overview]
A perennial that sometimes reaches about 2 m in height.
It has a large, flattened-spherical corm, and forms small corms.
Only one leaf emerges each year, growing to about 1–1.5 m tall.
The leaf is divided into 3 lobes, and each lobe is further divided into irregular pinnate segments.
The number of leaflets increases in proportion to the age of the plant.
The leaf stalk is thick and cylindrical, with mottled markings.
The leaf dies back in autumn, but the corm gradually grows larger.
The plant does not flower until the corm has grown to a certain size, which takes about 3–4 years.
When it flowers, no leaf emerges; instead a flower stalk 0.5–1 m tall arises from the base and bears a spadix enclosed in an ovate spathe.
The spathe is green at the base and dark purplish brown with mottled markings inside, and has a pointed tip.
The spadix has a long conical appendage and a distinctive odor.
The flowers have no petals and are densely arranged on the spadix, with female flowers in the lower part and male flowers in the upper part.
Once the plant has flowered, it can no longer produce offset corms (seed corms, small corms).
The fruit is an oval berry that ripens to orange.

[History]
It is said to have arrived in Japan together with the introduction of Buddhism, and is recorded in documents from around the 10th century, though some theories hold that it arrived as early as the middle Jomon period.
Production spread after 1776 (An'ei 5), when Nakajima Toemon devised a method of milling and processing it in Naka District, Mito domain.

[Uses]
Konnyaku is made from the corm, and the corm is also used as a thickening agent.
Raw konnyaku corms have a strong harshness caused by oxalic acid and other substances, so they require preparation before being eaten.

[Cultivation]
Propagate by small corms and from seed.
It requires an average annual temperature of around 13 °C and 1,000 mm of precipitation during the May–October growing period, so cultivation in cold regions is difficult, and the northern limit is southern Tohoku.
The optimum temperature is around 22 °C, and photosynthesis proceeds well in the range of 17–27 °C.
It dislikes strong direct sunlight, so it prefers partial shade and fertile clay soil that is well drained and retains water well; deep cultivated soil is better.
It also falls over easily, so a windbreak is desirable.
When planting, pay attention to the orientation of the corm, and place it with the hollow containing the bud facing up.
It is also good to plant it at a slant so that water does not collect in the hollow.
It is sensitive to both dryness and excess moisture; for plants in the ground, rainfall is sufficient unless summer brings a long spell of sunny weather and severe dryness, and for potted plants, water after the soil has dried.
Apply organic fertilizer as a base fertilizer, and as a top dressing around July during the growing period.
The corms are best harvested when the stems and leaves have turned yellow all over and 70–80% of the plants have fallen over, generally around mid-October.
Dig them up on a sunny morning when the field is dry, and leave them in the sun for about half a day.
For storage, place them with the buds facing down or sideways in a well-ventilated place, keeping them at 8–12 °C and 70–80% humidity.
Pests and diseases include bacterial rot, leaf blight, southern blight and root rot.

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