Onion Planting
Vegetable Farming in South Africa
Propagation
Onions are propagated from seed, either by raising and transplanting seedlings or by direct seeding. It is generally more successful to raise and transplant seedlings than to sow directly.
Seedbed soil needs to have a fine texture Seeds should be sown in rows to ensure enough ventilation and facilitate weed control.
Furrows should be 15 cm apart and the seed should be sown at a depth of 10mm to 15mm. Sowing densities should be between 1500 and 2500 seeds per 1m2. If the temperature is high at this time, cover the seeded area with a thin layer of grass mulch. Remove this mulch when the plants start to appear 7 to 14 days after sowing.
When the seedlings are 8mm to 9mm in diameter and 12 cm to 20cm in height they are ready to transplant. Short-day onions should be ready for transplanting between 6 weeks and 8 weeks.
Planting Method
To transplant, score furrows 2cm to 4cm deep in the ground and lay the white part of the seedling in the furrow. Don’t trim the leaves. Cover the roots with a rake and compact the soil around them. Do not plant the seedlings too deep as this could cause bulbs to become elongated. Keep the soil moist for five days, once the plants are in the field to allow the root system to settle.
Spacing
Plants should be spaced 8 to 10 cm apart in rows that are 20 to 25 cm apart. This is between 50 and 60 plants per m².
Sowing Time
Ideal Time: February - March
Possible Time: January - April
Planting Time
Sowing should take place before end March so that plants can be transplanted out into the fields in May and June.
Growth Period
Harvesting takes place 180 to 230 from sowing or between 100 and 120 days after plants are transplanted. Harvesting should commence when 50 to 60 percent of the leaves have lodged (flattened to the ground).
Fertilization
When preparing soil for planting the soil may require additional Phosphorus (P) in the form of a super phosphate. Normally a balanced N:P:K mix like 2:3:4 can be applied at 1000 kg per hectare and should be sufficient. After 3 weeks from planting and again after 6 weeks from planting a good mix of Potassium (K) nitrate (N) can be applied at 150 to 250 kilograms per hectare.
Irrigation
Approximately 500 to 600 mm of irrigation is required during the growing season of an onion. This should be around 35 to 40 mm per week. If the soils are very sandy then slightly more at shorter intervals may be required. Onion roots are concentrated in the upper 30 mm of soil and for this reason the soil must be kept moist. Do not water onions for three weeks prior to harvesting.
By
Louise Brodie