How to grow onions

Onions can be grown in a wide range of climatic conditions; they are quite hardy and can tolerate temperatures as low as -6⁰c.

However, good bulb formation requires temperatures from 15.5⁰c with an optimum temperature of 21- 27⁰c.

Soil Requirements

•      Onions do best in well drained soils that are at least 650mm deep, shallow soil may be utilised, but with adoptions in management practices.

•      Ensuring a PH range of 6.02 – 6.8. Lower PH levels can result in problems in regard to micronutrient uptake.

Seedbed Preparation

•      On well-drained soil, prepare a fine and even seedbed.

•      It is advisable to use seedling trays to ensure that little or no seed is lost during this process.

•      Commercial plant raisers can help farmers raise healthy seedlings for use.

Fertilizer applications should be determined by soil analysis.

Most onion roots are in a 15cm radius from the stem and are therefore shallow feeders.

If the soil pH is less than 6 or the available calcium is less than 2300kg per hectare, apply and incorporate agricultural lime at the rate of 2500kg per hectare about 8-12 weeks prior to planting.

Lime requires time to react with acid soil to raise the Ph.

In soils low in phosphorous apply and incorporate approximately 94kg of phosphate per hectare.

Generally, it is suggested that the phosphate be banded 6- 8.5cm below and on both sides of the rows where onions will be planted.

Nitrogen applications are critical in terms of quantity and timing of application.

The amount of nitrogen supplied depends on the soil analysis.

Poor soils may require up to 180kgs / hectare for direct sown crops.

Average soils would need lower levels – 120 – 140kg/ hectare.

Soils lows in Potassium require an application of 100kg/ hectare before planting.

The remaining potassium can be applied with the first nitrogen application at a rate of 85kg/ hectare, (three weeks after transplanting or when seedling has reached 3- leaf stage)

In applying pre- plant fertilizers it is best to band 6to 8 cm below the seed or transplant, rather than broadcasting and incorporating.                                                                                   

Transplanting

Seedlings are usually ready 5 to 6 weeks after seedling, when a majority of the seedlings necks are pencil – size (65 -80 mm) in diameter, 10-15 cm tall.

Plant spacing: 15-20 cm between rows x 8 cm within rows.

Irrigation

Irrigate 3-5mm daily after transplanting so as to keep the soil cool and moist.

Direct seeded onions growing under hot dry conditions may require two irrigation cycles per day.

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.

Do not over-irrigate as onion bulbs that are over-watered tend to be soft with a poor shelf life.

 Weed Management

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 only registered products.

 Pest and disease Control

Trips are the major pest in onions, if not controlled they can cause reduction in quality and quantity of produce.

A number of diseases do attack onions but the major ones include; Downey mildew and purple blotch.

Most diseases that occur in onions can be controlled through management practices, by growing resistant cultivars and chemical sprays.

Harvest when about 50 percent of the plants have dropped.

The onions are lifted mechanically or by hand and in windows for drying on the land.

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