Sword Bean is a perennial or annual, fast-growing, heavily producing, climbing vegetable. It is widely cultivated in the humid tropics of South and Southeast Asia but world-wide it remains a minor vegetable due to its toxicity when eaten uncooked.
Young Sword Bean green pods and leaves are eaten sparingly as a cooked vegetable. This crop is most useful as a cover crop that fixes nitrogen, and as a drought tolerant green manure. The vines and seeds, good sources of protein and starch, can be fed to livestock but only in small amounts. The level of toxicity increases with maturity of the plant.
- Elevation: 0 to 1500 m.(4500 ft)
- Rainfall: 700-4200 mm ( 27-165 in), a long taproot grows deep for soil moisture
- Soil types: low quality, acid (pH 4.3-6.8), tolerates some salinity and waterlogging
- Temperature, range: 15o-30º C (59o-86 º F)
- Day length sensitivity: some varieties require short days to flower Sword Bean seeds germinate readily.
Plant seeds 5-7.5 cm (2-3 in) deep, 45-60-cm (18-24 in) apart in rows 75-100 cm (30-40 in) apart to allow for spreading growth or provide trellis support. This crop can grow in light shade under trees to serve as a nitrogen-fixing cover crop.
Harvesting and Seed Production
Sword Beans are fast growing. Young pods are available for picking 3-4 months after planting at 10-15 cm (4-6 in) long, before pod swelling occurs. Ripe seeds require 5-10 months to mature and the pods will break open and scatter the seeds when ripe. The dried seeds store well as they are not attractive to insects.
Pests and Diseases
Sword Bean is usually resistant to diseases and pests. However, it is occasionally subject to a root rot disease, fall Army Worm and stem-boring beetle grubs. Destroy vines at the end of the harvest season and rotate with other crops to assist in pest and disease control.
Cooking and Nutrition
The young leaves, stem tips and immature pods with seeds may be cooked and eaten after draining off the cooking water. Mature seeds are toxic and must not be eaten unless they are extensively cooked (3 hours or more recommended) preferably using 2-3 changes of water, and the tough seed coats are removed. Cooked mature seeds have little flavor and a mealy texture, reducing their appeal as a human food source. Dried seeds can be detoxified if they are fermented to produce a product called tempeh. The concentration of these growth-inhibiting substances increases as the plant tissues age and mature.