Onion farming

How to grow, transplant, harvest and cure onions

There is no shortcut to success with onion growing. For you to get a good harvest, you must perfect the processes and follow them religiously, understand your market and know the weather patterns. Below find the key factors:

1) Soil test

Do a soil test to know if your land is ideal for growing the crop;

2) Choose your variety carefully

Have the following considerations:

  • Your market: Where and to whom you will sell your onions. Knowing your market will determine the decisions you make like the size of onions required, and so on. This will ensure that you are not stuck with a product you cannot sell.
  • Hybrids seeds vs non-hybrids: Some hybrid varieties produce more and are resistant to some diseases. They, however, require a farmer to be keen and precise in carrying out his or her practices. Different varieties are suited to different regions. Ensure that you plant a suitable variety.
  • Daylight hours: Long-day onions need about 14 to 15 hours of daylight to bulb. Short-day onions need 10 hours of daylight. Day-neutral onions form bulbs regardless of daylight hours and produce well in almost any region.

Pay attention to this because if you live where day length never hits 14 hours (for instance, in certain European countries), long-day onions will never form a bulb.

  • White, yellow, or red onions: They vary in flavour, pungency, and price. If you intend to sell in the open market, red onions are more popular. Some hotels will buy both white and red onions with white ones retailing at higher prices.

3. At the nursery

The practices that you carry out on your farm will be the second most important thing. As with most crops, if you fail to do the right thing at the right time, you are likely to fail.

Seedbed preparation:

  • Onions will take between 45 and 60 days in the seedbed. During this time, they need close monitoring and regular watering or rainfall. Plant your seeds when the rains are expected and store some water just in case the rains fail or delay. According to a Uasin Gishu farmer, Mr Athanas Tuiyot, the best time to sow seeds in the seedbed in Kenya is in August so that you will transplant them in October to coincide with the short rains.
  • Locate your nursery in an area close to water, with good soil conditions, and not previously planted with crops like garlic, onions, tomatoes, etc.
  • Start preparing your seedbed (tilling) a month before sowing to expose the pests hiding in the soil to the sun. Ensure your nursery has a fine tilth and that it is level.
  • Beds should be one-metre wide and five to 10 metres long (you can make this longer if you wish). Depending on soil type and moisture conditions in your area, your nursery bed can be raised (two to four inches high), sunken, or flat. Raised beds are most common as they reduce the risk of over moistening the beds.

Seed treatment:

Where possible, soak your seeds in an optimizer 30 minutes before planting to help them break dormancy, increase the vigour of seedlings, and ensure uniform, high percentage germination. A farmer from Matu in Kitui County, Ms Jane Kadogo, recorded minimum germination from her nursery in her first attempt at planting onions. However, not one to give up easily, she made a second attempt, but this time soaked her seeds in the organic fertiliser, DI Grow, before planting. To her delight, her seedbed recorded over a 90 per cent germination rate.

Agronomist Dennis Rapongo, however explains that the combination of nutrients in the optimiser or the foliar feed is what breaks seed dormancy. It is, therefore, important to consult an expert, as not all foliar feeds will result in successful breaking of dormancy.

Seed rate:

80-100gm/1mx5m bed (for seeds >90% germination), 1.5 to 1.6 kg/acre


Make furrows using a stick or your fingers 0.5 to 2cm centimetre deep. Spacing between rows should be 10 to 15 centimetres. You can mix your seed with sand at a ratio of 2:1 (sand: seed) for more uniform sowing.

Fertiliser application:

During planting, mix your soil with DAP fertilizer at a rate of 20gms-30gms per square foot or apply well-prepared manure.


After planting, cover your bed with about three to five centimetres of dry grass. Do not use green grass or broad-leaved materials to cover the beds. This grass cover should be removed after the seedlings emerge. Do this in the morning or late in the afternoon.

Seedbed management

Avoid the use of herbicides in the nursery. Instead, weed regularly. Water your bed twice a day in the morning and in the afternoon until two weeks after the seedlings emerge.

Thereafter, once daily until they are ready for transplanting. If the weather is too hot, try to water them twice a day until transplanting. Your onions will take six to seven weeks before they are ready for transplanting.

4.Practices at the farm:

Begin tilling your farm in preparation for transplanting when your seeds have been in the nursery for four weeks. This provides adequate time to expose any soil pests in your main farm to the sun. Depending on the soil test results, add manure and lime as onions are very sensitive to soil pH. Ten days after ploughing, till again using a harrower to get a fine tilth. The second tilling should fall about two to three days before transplanting.

Immediately after the second tilling, start making furrows at a spacing of 30 centimetres between rows and 5cm to 10cm between seedlings. Plant in full sun, and water them adequately. Wet your seedbed to ensure minimum damage to the seedling as you uproot them for transplanting.

Add DAP fertiliser at a rate of 100kg/bag or one small teaspoon per hole. Mix it with the soil. Apply a thin layer of mulch around the plants. For small farms, seeds can be sown directly. However, they are likely to require thinning at about three to four weeks.

Managing your farm:

Water and weed regularly. You can weed by hand or using selective herbicides, which are best applied between seven and 14 days after transplanting.


Onions need a lot of nutrients, especially, during bulb formation but over-fertilisation should be avoided. At two to three weeks top-dress with CAN, or NPK 26:0:0 or Urea at 75-100kg/acre.

Carry out a second top dressing after three weeks. This time use NPK (Nitrogen, Phosphorus and Potassium) commonly called triple 17 or NPK 23:23:23. However, adjust the amount as 23:23:23 has a higher percentage of the nutrients than 17:17:17. The general amount for 23:23:23 is about 50kg/acre and 75kg/acre for 17:17:17.

Onion development:

Onions will develop their leaves first, then depending on the variety and the day length, they will begin forming bulbs. As soon as the day length hours of onions are achieved, they stop forming the top and start forming bulbs.

To harvest good-sized onions proper feeding is important. The number and size of the green leaves or tops at the time of bulb maturity will give you an idea of the size of the bulb you will harvest. For each leaf there will be a ring of onion; the larger the leaf, the larger the ring will be.

Commonly grown varieties:

Some of the most commonly grown varieties in Kenya are Neptune F1, Russet F1, Sivan F1, Red Creole F1, Red Bombay, Red Pinoy, and Texas Grano. The have the following good characteristics:

  • Early maturing;
  • Have uniform bulbs;
  • Extended shelf life;
  • Better pungency;
  • Drought-resistant;
  • Disease-resistant.

Common pests and diseases:


  • Leaf miners
  • Maggots
  • Nematodes
  • Thrips

Thrips are notorious and severely attack the onions in both the nursery and the farm, causing a lot of damage. They can be controlled by integrated pest management (cultural, biological), or chemical methods. Chemical methods should be used as a last resort. In addition, overhead irrigation and the use of blue insect traps also help control them.

ALSO READ: why-tanzanian-onions-are-preferred by Kenyans. 


  • Downy mildew
  • Bacterial soft rot
  • Pink/White bulb root
  • Botrytis
  • Rust

These diseases, if not controlled cause significant losses.

Good crop nutrition:

Farm hygiene (keep your crop free from weeds) As a last resort, use pesticides and fungicides or bio-pesticides (for organic farmers), as recommended by the agronomist.


  • Harvest onions when they are mature as they have less moisture and are less prone to rotting. Mature onions will begin dropping their leaves, but farmers must be careful because onions will also drop their leaves if they are heat stressed;
  • The last three weeks before harvest should be absolutely rain-free;
  • Bend the leaves of your mature onions about 10 to 14 days before harvesting to speed up the drying;
  • Curing: When the leaves are completely dry, uproot the onions and leave them on the ground to continue the curing process for five to 10 days, as long as there is no rain. Cover them slightly with dry mulch to protect them from the sun;
  • If drying indoors, spread in a well-ventilated room for two to three weeks. Ensure that they are one foot away from the walls to provide for good movement of air.
  • Well-dried onions: necks become tight, and the outer skin becomes papery and emits a rustling sound when you rub it with your fingers. The skin colour will also be uniform.
  • Storage: When your onions are dry, store them in a cool dry well-aerated place (1.1 to 10 degrees celsius with 50 to 60 per cent relative humidity) and away from produce that releases moisture like potatoes.
  • Inspect your onions regularly for bulbs that are soft or rotting. Grade them according to the different qualities so that it will be easy for you to sell them in the market.

Mr Joshua Mouti, BSC Horticulture, Egerton University,
Post graduate Diploma in crop protection of vegetables and fruits
Email: moutijoshua@gmail.com Cell: 0719 212 112


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