Psophocarpus tetragonolobus (winged bean, "Shikakumame")

Japanese name: シカクマメ （四角豆）
Scientific name: Psophocarpus tetragonolobus

[Overview]
A climbing perennial, but because it is sensitive to cold it is treated as an annual in Japan.
It forms tuberous roots underground.
The stems grow up to 3–4 m tall.
Leaves are alternate and trifoliate, with long leaf stalks.
The flowers are pea-shaped, borne in the leaf axils, and white, pale purple or blue.
The fruit is a pod 15–30 cm long, square in cross section, with wing-like frills along the ridges.
The pods are green or reddish purple.
Each pod holds 5–20 seeds.

[Uses]
The leaves, flowers, pods, mature seeds and tuberous roots are edible, but in Japan eating the young pods is the most common.
The seeds are used medicinally.

[Cultivation]
Propagate from seed.
Because it spreads widely, allow about 50 cm between plants, or leave the main vine and several side vines and pinch off the axillary buds.
As long as the site is sunny, airy and well drained, it is not particular about soil.
It is prone to problems from continuous cropping, so do not plant it in soil where a legume was grown the previous year.
Water thoroughly when the soil surface dries.
Once pods begin to form, top-dress with a quick-acting chemical fertilizer every 2 weeks, or apply diluted liquid fertilizer once a week in place of watering.
When the vines start to grow, put up stakes or netting.
If left alone it spreads rapidly and the vines tangle, so tidy the vines frequently.
Harvest young pods (about 10–15 cm long) about 2 weeks after flowering, while the fibers have not yet developed.
If harvest is late, they become hard.
Nematodes are among the pests.

[Notes]
The Japanese name derives from the square cross section of the fruit.

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