Bush forms of velvet bean grow rapidly, but have a more compact growth habit than vining types. The leaves are large and trifoliate with lateral leaflets 7–15 cm long, 5–12 cm wide. Flowers are light purple or white, resulting in pods 4-13 cm in length. Wild forms of velvet bean have pods with hairs that, due to a protein called mucunain, are irritating to the skin and can cause severe itching; cultivated varieties (var. utilis) have non-stinging hairs. Mature, dry pods have a hard shell with each pod containing 4-6 seeds which, depending on the variety, vary in color (from black to white, brown, or mottled) and are 1-2 cm long.
Velvet bean fixes nitrogen and is, thus, widely used for soil improvement as a green manure cover crop. It also produces high biomass, though not as much as vining velvet bean. Bush velvet bean is less likely than vining velvet bean to climb adjacent plants, limiting its ability to suppress weeds but making it an excellent choice for intercropping between rows of maize. Though the seeds have been used as a coffee substitute, human consumption is not generally recommended due to the presence of antinutritive substances including L-dopa, a compound used to treat Parkinsons disease that is toxic if not taken in correct doses. Velvet bean seeds, pods, and foliage are used in a variety of ways as animal feed, usually as a supplement for ruminants; exercise caution by consulting the literature for appropriate quantities, feeding in small amounts, and taking any needed steps (e.g., ensiling, fermentation) to reduce L-dopa. Velvet bean is also noted for suppression of nematodes.
- Elevation – Up to 2100 m
- Rainfall – 400-2500 mm/year; a good option for the humid tropics
- Soil Types – Prefers well-drained soils with pH 5-8, intolerant to water logged soils
- Temperature Range – 19-27° C.
- Day Length Sensitivity – Shorter days induce flowering and rapid decline of vines
- Light – Prefers full sun
The large seeds germinate quickly. Sow them 3-7 cm deep with 1 m between rows and 20–80 cm (closer to 20 cm for bush velvet bean) between plants (this spacing requires 20–40 kg/ha of seed). Seeds do not require scarification or inoculation with rhizobia prior to planting. If interplanting bush velvet bean with maize, the beans should be planted a few weeks after the maize to minimize competition; but they can be planted sooner than vining . Plants of bush types may not persist in the field as long as vining varieties. Seeds left on the ground will regrow.
Harvesting and Seed Production
Seeds mature 100-280 days after onset of flowering with most varieties. Pods should be picked after turning dark brown or black.
Pests and Diseases
There are few pest problems due to production of toxic compounds.
Cooking and Nutrition
Velvet bean grains can be toxic to humans and non-ruminant animals. Extensive soaking and boiling is required for human consumption. Anti-nutrients include alkaloids, trypsin, phytate, lectins, saponins, and L-dopa.
Cook et al. 2005. Tropical Forages: an interactive selection tool. [CD-ROM], CSIRO, DPI&F(Qld), CIAT and ILRI, Brisbane Australia
Jorge et al. 2007. Mucuna species: Recent Advances in Application of Biotechnology. Fruit, Vegetable and Cereal Science and Biotechnology 1(2):80-94
Mapiye et al. 2007. Utilisation of ley legumes as livestock feed in Zimbabwe. Tropical Grasslands 41:84-91