Bang Kwang

Other common names: Bangkuang, Jicama, Mexican Turnip, Sengkuang, Yam Bean

Bang kwang is a large, climbing vine that is harvested for its starchy tuber. The tuber can be eaten raw, stir-fried, or steamed in a variety of dishes, and is most well-known as a component of rojak and popiah in Singapore.

An annual crop, these plants are often grown in rotation with other fruiting climbers.

This plant is part of the Fabaceae or bean family, which includes other popular edible fruits like winged bean, peanut, and sword bean. All members of the bean family can be used for companion planting as they can fix nitrogen into the soil.

Sun and soil needs:

This vine does best in full sun gardens with a minimum of 6 hours of sunlight. It can also grow in areas with at least 6 hours of indirect sunlight, but growth may be slower.

Plants do best in pots with loamy soil at least 30cm deep, or in true ground.

This vine is vulnerable to heat stress during the dry season. Water it regularly and mulch the base to prevent water loss.

Sowing Seeds

Seeds can be sown directly into pots or the ground around 15-30cm apart. Lightly water the soil until damp, once a day. Seeds should sprout within 10 days.

The seedlings are generally resilient to most environmental factors but may be vulnerable to being eaten by snails or birds. Protect your young plants with a DIY cloche or netting.

Growing:

Bean plants generally don’t require much fertilising because they are able to fix their own nitrogen. However, they do benefit from being fed high potassium and phosphorus fertilisers once a month after their first flower to encourage additional root and tuber growth.

Because the vines will grow on top of each other, it is a good practice to prune regularly and remove dead leaves and vines to improve ventilation and allow light to reach more of the plant.

As a fast-growing vine, this plant needs to be trained up a light trellis. The vine readily produces flowers and can be used to beautify fences and arch trellises.

Harvesting:

Tubers can be harvested around 5 months after sowing. Take note that once tubers are harvested, the rest of the plant will die.

Be aware that the skin of the tuber, leaves, fruits, flowers and stem are highly toxic. Ensure that the tuber has been scraped clean of skin before consumption.

Dry, brown seed pods are mature, and can be harvested for seeds to plant.

Harvest cycle:

Propagation:

This vine can be grown via seeds. Seeds can be taken from mature fruit for immediate planting.

Common problems & solutions:

Young plants have soft stems and can be completely eaten by slugs and snails. Grow seedlings till they are at least 10cm tall before planting them in true ground, or use DIY cloches or netting to protect young plants.

Aphids, mealy bugs, whiteflies, and spider mites often infest the plant if it has underlying problems like repeated wilting from heat stress. Mechanical pest control methods like pruning the infested parts are the best methods for managing these pests in the short term, but resolving the underlying problem will prevent them in the long term.

Wilting leaves during hot weather is a sign of heat stress. Increase the number of times the plant is watered daily, and apply mulch at the base to prevent water loss.