Planting, care and harvesting of onions

Onions can be planted on a commercial or small scale. Under good management, 20-25 tonnes can be realised from one acre. All you need is suitable soil. Well-drained sandy or loam soil with a pH range of 6.0-7.0 is ideal.

Plant onion seeds in raised beds before transplanting. You need 2-2.5 kgs of seeds to produce enough seedlings to plant in one hectare. The seedbed should be covered with mulch to conserve moisture.

Select a location with full sun where other plants won’t shade your onions. The more energy they can get from the sunlight, the larger their bulbs can grow. Prepare the planting site early enough and add animal manure to improve soil fertility. Transplant the seedlings after six months or once they are 15 cm tall. Ensure the nursery bed has enough moisture before transplanting to minimise root injury. Plant the transplants 30 cm between rows and 12 cm from one seedling to another.

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Should you want to harvest some of the onions during the growing season as green onions, you may plant them as close as two inches apart. Before they begin to bulb, pull every other one, leaving some for more giant onions. Practice crop rotation with onions. In other words, don’t plant them in the same location year after year, as this can encourage the spread of diseases that affect the crop. 

Fertilisation of onion plants is vital to success. Research findings indicate that onion growth and yield can be greatly enhanced by banding phosphorus 2-3 inches below seed at planting time. This phosphorus acts as a starter solution that invigorates young seedlings’ growth. Once established, onion plants should receive additional amounts of fertilizer (21-0-0 - Ammonium sulfate or Ammonium nitrate) as a side-dress application every month.

Onions have shallow roots and, therefore, are not efficient at taking up moisture, so they need a steady water supply to grow. Although they recover well from drought and start growing again when watered, it is best to keep the soil constantly moist until the bulbs increase.

Apply a layer of mulch such as maize stover, grass clippings, and any other materials that are herbicide–free. As onions form the bulbs, they naturally push towards the surface, and it’s best if the tops of the bulbs are allowed to bask in the dry sun. Therefore, remove mulch that might keep the expanding bulbs excessively moist.

Thrips are common pests in onions, which suck sap from onion leaves. These are hard to see because they hide down in the folds and neck of the leaves. Also, be on the lookout for aphids. Finally, weak plants that slowly wilt indicate onion root maggots, the larvae of a common fly, are present. Should you notice these signs, seek advice for the extension workers.

You can harvest young onions just a few weeks after planting if you use them as “spring onions” or scallions. There is no perfect size; pull when big enough to serve your purpose.

For full-sized bulbs, let onions grow and mature. Onions are ready to harvest when the bulbs are big, and the tops turn yellow and fall over. Pull them up, shake off the soil, and lay them out to cure with the tops still attached. Any warm, airy location is an excellent place to do this; you can even sling them over a fence as long as the rains can’t reach them. Bulbs should be kept dry and have good air circulation.