Winged bean (Psophocarpus tetragonolobus), a member of the family Fabaceae, is one of the most nutritionally complete legumes cultivated in Sri Lanka. Almost every part of the plant is edible — pods, leaves, flowers, shoots, and tuberous roots — making it an exceptionally versatile crop for smallholders and home gardens alike. With improved varieties now available, growers across the island can achieve year-round yields rather than depending on a single seasonal flush.
Which varieties of winged bean are recommended for Sri Lanka?
Two improved varieties are currently in common use, each suited to different grower preferences.
- SLS 44 — Produces white flowers and green pods weighing around 15 g each. Seeds are cream-coloured. This variety performs throughout the year and is a reliable choice for growers who prefer a milder-flavoured pod.
- Krishna — A high-yielding variety with distinctive purple flowers and purple pods that reach approximately 27 cm in length. Seeds are dark purple. The first harvest can be taken roughly 70 days after planting, making it one of the faster-maturing selections available.
Older, locally selected varieties are still grown in many areas, though they are typically sensitive to day length and may only produce during the Maha season. The improved varieties above were specifically developed to overcome this photo-period limitation.
What climate and elevation suit winged bean cultivation?
Winged bean is adaptable to a broad range of environments. It performs well from sea level up to around 2,000 m above mean sea level, covering lowland wet and dry zones as well as mid-country highlands. The crop grows best where temperatures remain between 18 °C and 32 °C. Areas with consistent moisture — either through rainfall or supplementary irrigation — give the most reliable results.
What soil type is best for growing winged bean?
Well-draining sandy loam or clay loam soils enriched with organic matter are ideal. The plant tolerates a wider range than many legumes, however, and can establish reasonably well in sandy soils or heavier clay soils provided waterlogging is avoided. On sites where water tends to sit after rain, raised beds or ridges should be prepared before sowing to protect root health.
How do I prepare land and plant winged bean?
Deep harrowing before planting breaks up compaction and improves drainage. Mark planting pits according to the recommended spacing of 75 cm between rows and 60 cm between plants. Before sowing, soak seeds in water for around 24 hours to encourage faster, more even germination. Treating seeds with a fungicide such as Captan at this stage can help protect against early damping-off.
Sow three to four seeds per pit. Once seedlings are approximately two weeks old, thin to the two healthiest plants per pit and remove the rest. Direct seeding at the onset of the rainy season is the most straightforward approach; where irrigation is available, planting can be timed more flexibly.
Seed requirement is typically 21–23 kg per hectare.
How should winged bean vines be trained and supported?
As a vigorous climbing vine, winged bean needs structural support to produce a good crop. Place a sturdy pole — around 7 feet (roughly 2.1 m) tall — near each planting pit. Train the young vines up the poles as they emerge. Adequate support improves air circulation around the canopy, reduces disease pressure, and makes harvesting considerably easier.
What fertiliser programme does winged bean need?
Begin by incorporating around 10 tonnes per hectare of well-decomposed organic matter during land preparation. This builds soil structure and provides a slow-release nutrient base. Apply basal chemical fertiliser two to three days before planting, then follow with two top-dressing applications.
| Application | Timing | Urea (kg/ha) | TSP (kg/ha) | MOP (kg/ha) |
|---|---|---|---|---|
| Basal | 2–3 days before planting | 45 | 215 | 65 |
| Top Dressing 1 | 4 weeks after planting | 20 | — | — |
| Top Dressing 2 | 10 weeks after planting | 20 | — | — |
The relatively high TSP rate at the basal stage reflects winged bean's phosphorus demand during root and nodule establishment. As a legume, the crop can fix atmospheric nitrogen through root nodules, but supplementary nitrogen at early and mid-growth stages supports consistent pod development.
How much water does winged bean require?
In dry weather, irrigate once a week. Sandy soils drain faster and can generally be irrigated less frequently than clay loam soils. Consistent moisture during flowering and pod-set is particularly important for maximising yield. Avoid over-watering, which can encourage root rot, especially on heavier soils.
How should weed control be managed during the crop cycle?
Winged bean grows slowly in its early weeks, making young plants vulnerable to weed competition. Targeted weeding is recommended at weeks 1, 3, 5, 7, and 12 after seed germination. Once the vines climb their poles and the canopy closes, the crop becomes more competitive against weeds and intensive management can be relaxed.
When and how are winged bean pods harvested?
Pods should be harvested every three to four days to encourage continued production and to ensure pods are picked at the tender, edible stage before the wings toughen. The improved varieties SLS 44 and Krishna typically yield a first harvest around 70–75 days after planting. Local unimproved varieties may take 90–100 days to reach the first harvest. Once harvesting begins, the productive window extends for a further six to seven weeks.
Regular picking is one of the most effective ways to maintain pod quality and extend the overall harvest period. Leaving pods on the vine too long signals the plant to slow flower production.
How does winged bean compare with other legumes grown in Sri Lanka?
Unlike many conventional legumes that are grown primarily for their seeds, winged bean offers multi-part utility. The young pods are used like French beans; older seeds can be dried and cooked like lentils or ground into flour; the leaves and shoot tips are consumed as greens; and the tuberous roots contain notably high protein compared with other root vegetables. This makes winged bean particularly attractive for mixed smallholder farming systems where maximising output from limited land is a priority. It is also increasingly of interest to researchers exploring drought-tolerant, protein-rich crops for tropical regions.