Onions can be grown in a wide range of climatic conditions; they are quite hardy and can tolerate temperatures as low as -6 0 c. However, good bulb formation requires temperatures from 15.5 0 c, with an optimum temperature of 21 0 c- 27 0 c.
Seedlings are usually ready five to six weeks after planting, when the majority of the seedlings' necks are pencil-sized (65-80mm) in diameter, 10- 15cm tall. This means that if you intend to plant onions at the end of July, you should plant the seedlings now.
Transplanting should be done either very early in the morning or late in the evening.
Transplanting when the sun is up affects the seedlings because it drains water from it. Plant spacing: 15-20cm between rows and 8cm within rows. An acre can take as many as 250,000 seedlings.
There are several ways of irrigating your onions. These include using the sprinkler system. It may be the small, low sprinklers; the water gun or drip irrigation system.
Of these systems, the sprinklers and the water gun are cheaper, since one unit can be moved from one part of the farm to the other, compared to the drip system, which is fixed on the farm.
Farmers can also use drip irrigation, however, this may turn out to be more expensive. A farmer can get a water gun, complete with a pump and pipes at sh3.5m, while laying a drip irrigation system on an acre may cost sh10m.
Irrigate 3-5mm daily after transplanting so as to keep the soil cool and moist. Direct-seeded onions planted from seeds without putting them through a nursery bed, growing under hot dry conditions, may require two irrigation cycles per day, in the morning and evening.
Water shortage at any stage during growth may result in decreasing yields. Adequate watering promotes good growth and helps keep the soil firm around the onions. You are advised to water three times a week. Do not over irrigate (this can be seen when stagnant water collects) as onion bulbs that are overwatered tend to be soft and have a short shelf life.
Onions develop slower than other vegetable crops and are more susceptible to weed competition, especially during the early growth stages. This can result in yield losses. Weeds can be controlled successfully through either pre- or post-emergence herbicides use.
Pest and disease control
Thrips are the major pest in onions, if not controlled they can cause reduction in quality and quantity of produce.
A number of diseases attack onions, but the major ones include downey mildew and purple blotch. Most diseases can be controlled through management practices such as growing resistant varieties and chemical sprays.
Harvest when about 50% of the plants have dropped and shrinked. The bulbs are also visible from the soil.
The onions are lifted mechanically or by hand and put down on the farm to dry. You then have to store them in a cool, dry well-ventilated store. They can last for up to six months. However, if it is processed into powder, it can last for between 12-20 months.
Compiled by Joshua Kato (Harvest Money Editor) and Abbey Kazibwe (from Nsanja Agro-chemicals)