Garden Tips

Planting and growing Onions

 Onion plant

                    Onion Plant

Although onions out of all vegetables are the most pest resistant, they take between four and seven months to grow and mature. This means that much of your garden space, resources and time are invested in growing one crop. Do you want to go so far as to grow your own onions?

So you have made the decision that you want to grow onions.

Where to start:

The start of owning a successful onion garden is to seek out the right place for your onion bed. This means that the patch must have enough sunlight and must have a temperature that will allow the onion bulbs to form. The second thing is to find the correct cultivar of onion for your part of the world and one that will thrive in your climatic conditions.

Onion cultivars and where they will grow:

Brown Skin onion

There are three types of cultivars to choose from.

Short day cultivars which include Hanna, San, Shahar, Red Creole and Texas Grano take between 220 and 230 days to mature. In South Africa these cultivars grow best in the area stretching from Bloemfontein northwards to Musina. Onions should be planted between February and March in this region.

The main intermediate cultivar is the Australian Brown Skin onion which takes between 250 and 280 days to mature and which can be sown in the area stretching from Kimberley southwards into the Western Cape. Other cultivars such as the Red Creole which is a short day cultivar and the Hanna hybrid can also be planted in this region with the best time to sow these cultivars being from April to the end of May.

Long Day cultivars are not grown in South Africa.

Soil requirements

Soils that have a heavy clay content should be avoided as onions like a soil that drains well. If you have a clay soil then you should make the ground more friable by adding compost to the soil and mixing it in. Because onions take a long time to mature it will also be necessary to mix in an organic fertiliser such as 3:1:5 before planting your onion plants.

Any stones or lumps of soil should be broken up or removed because onions grow best in fine soil. Onions belong to the family called Alliums which include the following : onions, garlic, leeks, shallots, chives. When planting a new onion garden the bed should not be planted where any of the alliums listed above have grown in the past three years. Onions grow to a depth of about 600 mm so it is not necessary to prepare the soil to a depth deeper than about 800mm.

Seed Requirements

If you are going to be planting seed you need to buy fresh seed as once a seed packet is opened the seeds start deteriorating. Older seed from previous seasons can be utilised to grow spring onions as the chances are good that not all the older seed would germinate and would spoil your chances of a good onion crop.

Sowing of your seeds

When sowing seeds two methods can be used. The first is to sow the seed directly into the bed you have prepared for your onions and the second alternative is sow your seed into seed trays. As onion seed is very fine it should be sown thinly over the bed and then covered by a 2cm layer of seedling mix which should be firmed down over the seeds.

For planting in seed trays sow four or five seeds per cavity which will ensure at least one or two plants germinating in each cavity.

In both cases above ensure that the ground is kept moist during the first six weeks of growth as the onions root systems are very shallow and soil drying out might cause them to die.


At about seven weeks or when you feel the seedlings are big enough to handle it is time to either thin out the plants that have been planted directly into the onion beds or transplant the onions growing in the seed trays.


Thin out the onion plants leaving the strongest plant in the soil with a gap of about 10cm between it and the next plant and a gap of 15cm between each row of plants. If you are not sure that a plant is strong enough to survive leave one or two plants in the gap you are creating and go back a few days later and remove the smaller plants which you can either transplant to another bed or use as spring onions in a salad.

Seed Trays

Lift each set of plants in the gaps in the seed tray and single them up using the strongest plant to transplant into the ground. Plant them in rows using the same gaps as listed in the bed planting method above. Don't throw away the weaker plants as they can be planted out as well, just keep them seperate from the stronger plants while transplanting as the chances are that some of them could die and leave gaps in the beds you are planting. Utilise any plants left over as spring onions in a salad or plant them in another bed.

Once you have planted out your seedlings feed them with some liquid fertiliser, compost tea or worm tea. This will ensure that the shock of being transplanted is overcome.


Onions are to be watered regularly and are to be fed monthly in the warm autumn months. A second chore is to weed your onion beds regularly to take away any competition your onions might have for food or sunlight.

In July onions grow slowly because of the low temperatures and some of the bigger plants might bolt as a result of the cold weather. As the weather warms up your onions should be watered more regularly. Remember not to overwater your onions or to allow your soil to dry out.

In August it is time to start feeding your plants again. Potassium rich fertilisers such as 3:1:5 should be applied or you could use a liquid fertiliser as well. To supplement the above you can use wood ash from your braai.

Onion plants do not have an efficient rooting system so it is necessary that you ensure that there are plenty of nutrients in the ground for them. If your onion's leaves start turning brown at the tips it means that there is a deficiency of potassium in your soil and not that the onions are reaching maturity.

To ensure that you get nice strong smelling onions you need to add a sulphur-based fertiliser. To enrich the soil and give your onions their much needed micro elements that are not always available in the compost you get today add a liquid seaweed extract to your fertilising regime.

Nitrogen rich fertilisers are harmful to your onion plants so avoid them. They can cause the onions to develop thicker necks which don't dry out with the result that an entry point is created for pathogens to enter the plant which can cause the onion to rot from the inside later on.

To keep your onions healthy spray the foliage with a copper based fungicide which will help ward off fungal diseases.


Over the past seven months you have sweated blood and tears to get your onions to this point. You want to harvest your onions at their best but you have no idea when the best time is.

Here's what you should do:

Your onion plant will tell you when its bulb is starting to reach maturity as its leaves will start turning yellow and start falling over. It is now time to start watering less. Once the majority of your onions have fallen over dig them up and allow the leaves to dry out before storing them. If you dig the onions up before they have reached this stage you might find that the bulbs have not formed properly and you will have a poor and small onion crop. What are the best times to harvest in South Africa

Between July and August onions growing in areas such as Musina, the Lowveld and parts of KwaZulu-Natal and Dendron should be lifted.

In September and October the warmer areas of Gauteng, North West, Limpopo and KwaZulu-Natal Midlands should be harvested.

During October and November the cooler areas of Gauteng, the Free State and Northern Cape should be harvested.

Onions growing in the Western Cape should be harvested in November and December.


To ensure that your onions last you should take some precautions to preserve them. Onions appear to be tough but in fact they are not as they bruise easily especially when they are fresh out of the ground. Once you have dug them up they should be left in the sun for two days to dry out. In very hot areas it may be necessary to protect them by covering them with straw.

In wet weather you need to bring them indoors for the drying out phase. Once they have been dried out you can plait the leaves of the onions together and hang them in a cool dry place such as your garage or storeroom where there is a lot of air movement.

The best onion for storage purposes is the brown onion as it will store longer than red onions.

I wish you luck with your onions.

Happy gardening.

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