Kenyan farmers lose up to 40 per cent of their onions after harvest because of poor curing seeing most brokers prioritise well-cured and dried Tanzanian onions.
According to research, Kenyan farmers lose 40–60 percent of the value of their onions after harvest. This is because they do not give them the required week to two weeks to cure and dry on their shambas before harvest. Farmers in Tanzania’s ‘onion capital’ of Mang’ola have however perfected this crucial part of the onion farming process which allows brokers to store their onions for months giving them priority in not only the Kenyan market but South Sudan’s and Ethiopia’s as well.
According to Joshua Mamwaka, an onion broker at Nairobi’s Wakulima Market, Kenyan brokers who buy 70 per cent of farmer’s onions prize two things over all else: medium-sized, well-cured/dried onions.
“Onions from Mang’ola in Tanzania get priority in Kenyan markets because they are predictably medium-sized and well-cured. This means I can store them and even the mama mbogas I sell to can keep them in their stalls for several weeks without fear of them rotting. Unfortunately, most Kenyan farmers do not invest the time, expertise, and labour in drying and curing their onions but rather want to sell them immediately after they harvest, especially if onion prices are high, deliver uncured and even immature bulbs which rot easily,” he explained.
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Boniface Kilu who has grown onions in both Kenya and Tanzania informs that onion curing starts even before the bulbs mature.
This is done by feeding onions with fertilisers rich in Phosphorus, Potassium, Calcium, and essential micronutrients Zinc, and Sulphur. Calcium makes the onion bulb firm enhancing their shelf life while Phosphorus encourages onion bulbs to reach maturity at the right time 2½ to 3 months for hybrid onions and three to four months for open-pollinated onion varieties (OPVs). Potassium for its part ensures bulbs have the expected weight and size
Sulphur, and Zinc micronutrients are also just as vital as they give the onion bulb its desired flavour and smell and also ensure bulbing isn’t delayed the crop can be stored for a long time and may not store well, the skin will not peel off and the bulb hardens and will not regerminate post-harvest.
To cure onions correctly, their water supply should be reduced gradually at weeks 10 and 11 before it is cut off at least eight days to harvest.
“The next step in curing is to fold or bend the onion leaves at the neck area (where the leaves meet the bulb. This should be done when 50-80 per cent of the onion leaves have fallen over on their own, indicating the onions are mature and ready for harvest,” Boniface explained.
Folding the leaves can be done by hand or running an empty drum over the onions. It forces the plant to stop feeding the tops, focusing on ripening and curing the bulb. The onion leaves also cover the bulbs avoiding them being hit by direct sunlight.
The onions should be left to cure in that position as long as they are not rained on and the field has good airflow to avoid rotting and speed up curing. They should however be harvested before two weeks to avoid soil-borne diseases and them going mouldy.
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Once the leaves are dried pull the onions from the ground cut them off an inch from the bulb and shave off the bulb roots before storing them in a building with plenty of air.
“Once they are cured, most hybrid onions have up to three layers of ‘dead’ outer skin compared to one in OPV onions which helps in their marketability. However, for their part, local onions can be kept for up to six months once they are well cured without rotting, a duration that hybrids often do not reach,” Kilu said.