Bunching onions are perennial (often grown as an annual), and are similar in taste and smell to their relative the common onion, Allium cepa. Though some cultivars have a slightly-thickened base (pseudostem), bunching onions rarely form bulbs. Thus, they are eaten as a green onion.
Thought to have originated in China, bunching onions spread worldwide and are an important crop in parts of Asia, Africa and Europe.
Bunching onions are used as a vegetable. They can be chopped fresh in a salad and are commonly used in stir-fry dishes. Cultivars in Asia (Japanese Bunching Group) are grown for their thickened pseudostems, while others (Welsh Onion Group; more common in Africa) are grown for their green leaves.
- Elevation – Bunching onions are a temperate crop and grow best above 500 m in the tropics
- Rainfall – Bunching onions need consistent moisture during the growing season
- Soil Types – Prefers well-drained soils with pH near neutral (will still grow at pH of 8 to 10; growth is poor in acidic (< 7) soil
- Temperature Range – 0 to 25° C; flowering rarely occurs in the tropics, requiring temperatures below 13 °C
- Day Length Sensitivity – Varies between cultivars; tropical conditions generally favor vegetative (leaf) vs. reproductive (flowers) growth.
- Light – Prefers full sun
Sow seeds in a seedbed, within 5 to 6 centimeter (cm) wide bands. When plants are about 25 to 30 cm tall, they can be transplanted to the garden or field at a spacing of 20 X 25 cm. Maximize the number of stems/shoots (tillers produced by the parent plant) by planting seedlings at an angle into manure-amended soil. In the tropics, where bunching onions rarely flower, propagation is done mainly by dividing the stems/tillers at the base of the plants.
Harvesting and Seed Production
Harvesting may be done continually once the plants have reached an acceptable size. The stalks should be washed thoroughly in clean water.
Seed production is usually done in temperate areas, as the plants need a period of cold or short days to initiate flowering.
Pests and Diseases
Bunching onions generally are not seriously affected by pests and diseases. Nevertheless, plants should be checked for insect pests such as thrips (Thrips tabaci), army worms (Spodoptera exigua), and bollworm (Heliothis armigera). Any diseased plants should be removed to prevent the spread of fungal diseases such as downy mildew (Peronospora destructor) and white rot (Sclerotium cepivorum).
Cooking and Nutrition
Bunching onions are eaten fresh in salads, and cooked in stir-fries and soups. In parts of Africa and Asia, whole plants are harvested and either boiled or steamed. They are a good source of Vitamins A and C.