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Understanding Storage Onions (Allium cepa)

GROWING SUMMARY​

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  • Onions are frost hardy and germinate best between

  • Timing:  

  • Direct Seeding

  • Growing Seedlings
    Germination temperature

  • Bed Preparation
    Raised beds
    On the flat

  • Plant Spacing
    Germination temperature

  • Irrigation
    Germination temperature

  • Pests and Diseases
    Germination temperature

  • Harvesting
    November – January depending on variety & location

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GROWING SUMMARY​

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  • Onions are frost hardy and germinate in around 7-14 days if the temperature is between 20-25°C.

  • Most keeping onions are sown in late autumn/winter the timing is dependent on both latitude and variety.  

  • Direct Seeding works well in places where the soil temperature is still fairly warm going into winter.

  • Growing Seedlings to transplant mid winter is a great option especially if the weed pressure is high. Make sure you are on top of rodents. They know exactly when the radical has emerged from the seeds and will systematically eat all of your emerging seeding over night.

  • Prepare the ground using plenty of compost. Onions like full sun, fertile soil and well drained soils. Grow them in raised beds if your soils are heavy. 

  • Traditionally they are planted in rows 50-100mm apart, 200-250mm between rows. However they grow just as well in clumps of 3-4 plants spaced on a 250mm grid which will make hoeing much easier.

  • Overhead irrigation is needed to get them started but drip works once established.

  • Adequate compost will minimise most soil borne diseases but onions can be susceptible to various fungi including an orange rust in warmer, more humid areas. Motitor the leaves carefully as the weather warms up and spray with a fungicide (wettable sulphur) if needed.

  • Harvest November–January once the leaves narrow above the bulb (neck) and fall over. Cure in a drafty, shady place until outer skins are very dry then remove the stems and store in a cool dry place.p Alternatively use the stems to to attach them to strings and hang from the roof.

VARIETIES​

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Onions are extremely location specific so talk to vegetable growing friends and neighbours and find out what varieties do well for them. Here are a few that are known to grow well in temperate Australia.

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  • Gladalan Brown & White  

  • Pukekohe/Cream Gold

  • Tropea Rossa Lunga

  • Red Shine

  • Hunter River Brown

Choosing Which Variety To Grow

Temperature and fertility do influence onion growth but the formation of the bulb is controlled by how much daylight they recieve. They are broadly divided into 3 categories:

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Short Day Onions Latitudes 25-35°

  • Start bulbing when daylength reaches 10-12 hours

  • Mature in 110 days when planted during winter in southern areas

  • Mature in 75 days when planted in northern areas in late winter but will end up being small

  • The earlier you plant them, the larger they get

 

Intermediate Day Onions Latitude 32-42°

     Moruya 36°S

  • Start bulbing when daylength reaches 12-14 hours

  • Will produce nice-sized bulbs in NSW

  • Mature in 110 days when planted at the proper time

  • Exceptionally sweet

 

Long Day Onions Latitude 37-45°

  • Start bulbing process when daylength reaches 14-16 hours

  • Do extremely well in Victoria and Tasmania

  • Excellent for long storage

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Weeds

Onions are monocotyledons (commonly referred to as monocots), grass-like flowering plants with seeds that contain only one embryonic leaf, or cotyledon. New, thin, hollow leaves emerge from the centre of the plant and unlike their cousins the leafy dicots they are never able to shade out the ground inhibiting new weed germination.  So the story is you will be weeding your onions from the time they are planted right through to harvest. The consequence of letting them become weed infested is  huge. At worst no crop at all, at best your onions will be much reduced in size.

 

Planting them in clumps of 3 or four plants on a wider spacing is an innovative, time saving way to grow them.  Quicker to plant and much easier to weed.

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Onions can be tricky but are well worth persisting with as they are so important in cooking. Find a variety that does well in your garden, stick with it but try out other varieties that may extend your harvest so that you have onions for your kitchen year round.

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