Growing Onions

Onions (Allium cepa) is a member of the Allium family and contains a number of sulfides that are similar to those found in garlic. Sulfides have antibacterial and anti-inflammatory actions that help to lower blood pressure and cholesterol, as well as helping to relieve colds, flu, sinus conditions and chest infections. It is these sulfides that also make you cry when chopping up onions.

Growing onions

Growing onions is straightforward, although they are one of the ‘longest’ crops, taking anything from 4-7 months from sowing to harvesting. This represents quite an investment in time, space and resources, but it means that you can grow varieties that are not always available in the supermarket. By July onions are halfway or more through their growing season, and it is from that point onwards that the crop really requires attention.

They need full sun and will grow in most types of soil. Seed can be sown in trays or in-situ, although trays may be easier to manage. The young seedlings transplant well.

Onions are generally disease and pest resistant, and although the growing period is long they just need regular watering, especially during the first few months of growth, and fertilising.


Success, however, depends on one thing: planting the right onion for the right area. Onions need a certain number of daylight hours and particular temperatures before they will begin to form bulbs.

There are ‘short day’ cultivars, others that are classified as ‘intermediate’, and still others as ‘long day’.

‘Short day’ cultivars such as ‘Texas Grano’, ‘Hanna’, ‘San’, ‘Shahar’ and ‘Red Creole’ are best planted in the area from Musina in the north down as far as Bloemfontein. The best sowing time is from February to the end of March.

‘Intermediate’ cultivars, such as ‘Australian Brown Skin’, are best sown from Kimberly downwards, including the Western Cape. The best sowing time is from April to the end of May.

‘Red Creole’ (short day) and ‘Hanna’ (hybrid) can also be grown in the areas suitable for intermediate cultivars – from Kimberly downwards, and again from April to the end of May.

If you don’t have a crop of onions in the ground at present then put it on your wish list – haul out your gardening diary and make a note of the best planting time in your region.

Fresh seed required

Onion seed tends to deteriorate as soon as a seed packet is opened, so it is necessary to buy fresh onion seed each year. If you have any seed left over from last year rather use it for spring onions so that a lower germination rate is not so disappointing. Spring onions are simply the seedling stage of bulb onions.


Set onions out in rows, with 15cm between the rows and 10cm between each plant in the row. Because onions have a shallow root system, they need space so that there isn’t competition for nutrients and water.

READ MORE: Need help with your veggies? Check out this list of frequently asked veggie questions and answers.

Soil requirements

Onions like soil that drains well. Heavy or clay soils should be avoided or made more friable with the addition of compost. Because onions are such a long crop, include an organic fertiliser (3:1:5) in the soil preparation. Once the bed has been tilled, rake it to remove any stones or clods of soil so that the texture is very fine. Don’t plant onions in a bed where other alliums have been grown in the past three years.

Watering onions

Water your onions regularly and well during the growing season and don’t let the soil dry out. Because the roots are shallow, they don’t need deep watering. Check to see how deep the roots go and water to that depth. Keep beds weed free so that the onions don’t have to compete for sunlight and nutrition.


Onions have high nutrient requirements and should be fertilised at regular intervals.

From August, as the weather starts to warm up, feed with a potassium-rich fertiliser like 3:1:5, or a liquid fertiliser. If the leaves start turning yellow at the tips it is an indication of a potassium shortage and not the onset of maturity. Do not use nitrogen-rich fertilisers as this can produce thicker necks, which don’t dry out properly and create an entry point for pathogens that can result in rotting later.

Harvesting onions

Generally, onions will indicate when they are ready for harvest. When the leaves start to turn yellow and fall over to one side it is an indication that the final phase of maturation has started, so taper off the watering. Once the majority of your onions have ‘fallen’ then dig them up and allow the leaves to dry out before storing the bulbs. If dug up before then the bulbs may not have formed sufficiently and they may not store successfully.

Great care needs to be taken when harvesting onions so that they have a long storage life. Onions are not as tough as they look and can be easily bruised or damaged when dug up.

Harvest schedule

Harvest times vary from region to region:

  • July to August in very warm, frost-free areas such as Musina, Lowveld, parts of KwaZulu-Natal, and Dendron.
  • September to October in warmer areas of Gauteng, North West, Limpopo and KwaZulu- Natal Midlands.
  • October to November in cooler areas of Gauteng, Free State and Northern Cape.
  • November to December in Western Cape.


Allow the bulbs to dry out before storing. Leave the onions on top of the beds for about two days to dry out in the sun. In very hot areas place straw or leaves over them to afford some protection from sunburn. If it is raining put the onions under cover to dry out. Once they have dried, store them in a cool, dry place where there is plenty of air movement.

READ MORE: Try making these spicy lamb burgers with raita and onion bhajis

The Gardener