July 2010
Know your onions

Onions (ALLIUM cepa) share their membership of the Allium family with garlic, leeks, chives, scallions and shallots. Besides containing vitamins A, B and C, as well as significant amounts of calcium, potassium and phosphorus, onions also contain 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 one cry when chopping up the onions.)

Growing onions
Growing onions is straightforward, although they are one of the ‘longest’ crops, taking anything from four to seven months from sowing to harvesting. This represents quite an investment in time, space and resources, but it means that you can have varieties that are not always available in the supermarket.
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 ‘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 Kimberley 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 Kimberley downwards, and are best sown 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 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.)

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. Do not plant onions in a bed where other alliums have been grown in the past three years.

Sowing
Sowing can be done in situ or in seed trays. It is easier to watch over the germination process and seedling development when using seed trays. The seed is very fine so it can be sown fairly thinly and covered with a 2 cm layer of soil or seedling mix and firmed down. Because the viability of onion seed is short lived, sow four or five seeds per cavity to ensure one or two plants. Onions store very well, so it is not necessary to do succession planting. Make sure the soil is kept consistently moist during the first five to six weeks of growth when the roots are very shallow.

Transplanting
When seedlings are big enough to handle, about seven weeks after sowing, they can be transplanted from the seed trays, or thinned out if planted in situ. For a medium-sized onion, space plants about 5 to 10 cm apart and rows 15 cm apart. For bigger onions the spacing can be wider. Thinning out can be done in two phases. The first seedlings removed can be transplanted elsewhere or snipped into a salad and the second lot can be used as you would spring onions. Give transplanted seedlings an application of liquid fertiliser, compost tea or worm tea, to help them overcome the transplant shock.
Water regularly and feed monthly during the warm autumn months and keep beds weed free so that the onions don’t have to compete for sunlight and nutrition.

Winter into spring treatment
In July growth is slow and although onions can cope with very low temperatures those that have grown too big might bolt as a result of cold weather. Start watering more regularly when temperatures begin to rise. The soil should not be allowed to dry out, but neither should the onions be overwatered.

From August, as the weather starts to warm up, feed with a potassium-rich fertiliser like 3:1:5, or a liquid fertiliser. One can add wood ash (from the braai) as a supplement. Their shallow root systems mean they are not very efficient feeders, so you do need to make sure that plenty of nutrients are available. If the leaves start turning yellow at the tips it is an indication of a potassium shortage and not the onset of maturity. For a more pungent tasting onion add extra sulphur by applying a sulphur-based fertiliser. Micro elements are not always available to plants growing in beds enriched with a lot of compost so it is a good idea to use a seaweed extract liquid feed.
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. Watch out for aphids and wash them off with a soapy liquid. Spraying with a copper-based fungicide will support the general health of the foliage, and ward off fungal diseases.

Harvest schedule
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 this stage the bulbs may not have formed sufficiently and they may not store successfully.
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.
Harvesting and storage
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. 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. Many onion growers store their bulbs by hanging them up in a garage or storeroom. The tops can be plaited before the foliage has completely dried out. Brown onions store better and for longer than red onions.

• Information supplied Andrew Dominy of MayFord Seeds (011 548 2800) and by Di-Di Hoffman of Bouquet Garni Nursery, potted herb grower and marketer. Visit Di-Di at www.gofoodgardening.com or phone him on 082 416 7145.