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Growing Onions in Australia: Step-by-Step Guide

The first thing you want to do is to choose a nice sunny spot in your garden to grow your onions. Improve the structure of the soil by incorporating some compost a few weeks before planting. 

Growing your own onions is fairly easy as they require minimal care once they’ve been planted. There are also different varieties that you can grow, depending on your climatic zone. 

When to plant onions in Australia

Onions are generally a cool climate crop and should be planted in autumn and winter. But which variety you choose, will depend on where in the country you garden.

Here are the different types of onions that you can grow depending on the amount of daylight hours that they need:

  • Early-season onions only need around 10 to 11 hours of daylight to produce bulbs
  • Mid-season varieties need around 11 to 14 hours of daylight
  • Late-season varieties will need around 15 to 16 hours of daylight

There are also some varieties that are daylight-neutral which means that the number of daylight hours they receive does not impact bulb formation.

As a general rule, gardeners in the southern states can grow all types of onions in their gardens. This includes white, brown, gold and red onions.

Growing red Onions in Australia | Fruit & Vegetables

However, gardeners in the northern states should concentrate on growing early-season onions as the amount of daylight hours doesn’t change all that much.

Here’s a general guide for when to plant onions depending on your climate:

  • Cool climate – Autumn, winter and spring
  • Mediterranean climate – Autumn and winter
  • Temperate warm climate – Autumn and winter
  • Sub-tropical climate – Autumn
  • Tropical climate – onions don’t grow well in the tropics

Not sure what climate you’re in? Check out our Australia Climate Zone Map (opens in a new tab).

If you’re growing from seed, you’ll find that seed packets will list whether the onions are early, mid or late-season varieties. They’ll also state the best time to sow the seeds.

onion seed packet | Fruit & Vegetables

How to plant onions

The first thing you want to do is to choose a nice sunny spot in your garden to grow your onions. Improve the structure of the soil by incorporating some nice compost a few weeks before planting. 

If the soil is nice and friable, it will make it easier for the onion bulbs to form and you’ll end up with larger bulbs.

Growing onions from seeds

The best way to plant onions is by sowing seeds directly into the garden. Here’s what to do.

Create a narrow and quite shallow trench. Onions seeds shouldn’t be planted too deep, otherwise, they won’t germinate. Around 6mm deep is sufficient.

Scatter the seeds as evenly as you can into the trench. Backfill only lightly with the excavated soil or cover the seeds lightly with seed-raising mix. The latter is preferable because it will make it easier for the new sprouts to break through the surface.

Firm the soil cover down gently and water to moisten.

planting onion seeds | Fruit & Vegetables

The seeds should start to germinate within 4 to 14 days. During this time, keep the soil moist but not wet.

Once the young seedlings are growing, it’s time to thin them out a little. This is crucial to avoid overcrowding and gives the bulbs plenty of room to grow.

onion seedlings | Fruit & Vegetables

When the young seedlings are around 10 to 12 cm tall, thin out the weakest seedlings so that you have around 10 cm of space between the remaining plants. 

Onion greens are also edible so you can use the young plants that you’ve pulled out like you would use spring onions in the kitchen. This means that the seedlings you’ve pulled out won’t be wasted.

Growing onions from purchased seedlings

You can also purchase punnets of seedlings from your local garden centre or nursery. These need to be separated gently and planted in a prepared garden bed.

To make this easier, I like to dig a trench and then lay the small seedlings in the trench at the recommended spacing (10 cm).

planting onion seedlings | Fruit & Vegetables

Then, it’s just a matter of backfilling the trench and gently firming the soil around each plant so that it sits upright.

Cover the soil lightly with some pea straw or sugar cane mulch. Water with a diluted mixture of seaweed concentrate. This will help to avoid transplant shock.

How to care for onions

If you’ve added lots of compost to the soil before planting, all you need to do is keep your growing plants well-watered.

watering onions | Fruit & Vegetables

You can give them a boost during their growing season by applying a liquid seaweed solution every two to four weeks.

It’s best not to feed your onions with a fertiliser high in nitrogen because this will promote plenty of green growth at the expense of large bulbs.

How long do onions take to grow?

Generally, it will take around 6 to 8 months for the onion bulbs to form and mature.

However, you can dig up some of the immature bulbs early in order to use the green growth in your cooking.

When to harvest onions

You’ll know that your onions are ready to harvest when the green growth has wilted and died down. This makes it really easy to know when your onions are ready to harvest.

harvesting onions 1 | Fruit & Vegetables

How to harvest onions

Onions are easy to harvest. All you have to do is gently dig up the bulbs once the foliage has died down. 

harvesting onions | Fruit & Vegetables

Place your freshly dug onions in a warm spot to allow them to dry out. They’ll be cured when the outer skin layer becomes papery. 

Store your onions in a cool, dry spot like in a basket at the bottom of your pantry. You’ll find that brown onions will have the longest storage life while white and red onions need to be used more quickly.

Onion pests and diseases

Although onions are fairly easy to grow, you might experience a few problems along the way which can generally be avoided or treated.

Poor bulb development

This is often caused by planting at the incorrect time or applying a nitrogen-rich fertiliser.

Make sure that you check the seed packet for the correct planting time in your zone and don’t apply a nitrogen-rich fertiliser during the growing period.

Rotting of onion bulbs

This is likely to be caused by a fungal disease and can’t be treated once it happens.

As fungal spores live in the soil, it’s a good idea to practice crop rotation and avoid planting your onions in the same spot year after year.

Onion fly

Onion flies often lay their eggs in any fresh organic matter that you add to the soil. When the eggs hatch, the maggots will attack and kill the young seedlings. 

Onion damaged by Onion fly | Fruit & Vegetables

To avoid this problem, make sure that you only use well-rotted compost and apply this to the soil a number of weeks before planting. Alternatively, you can add some compost after planting and once the plants are well-established.

Onion companion plants

Onions make great companions for many of the other vegetables that you like to grow in your garden. Some of the best companion plants for onions include:

  • Beans
  • Beetroot
  • Tomatoes
  • Leeks

Can you grow onions in pots?

If you have limited outdoor growing space, you can certainly grow onions in pots.

It’s best to choose a large pot that is at least 50 cm in diameter and around 30 cm deep. This should accommodate around 10 to 15 onion plants.

Onions growing in pot | Fruit & Vegetables

Make sure you use a premium potting mix and keep it nice and moist but not overly wet. This means that the pot you choose should have plenty of drainage holes.

Place the pot in a nice sunny spot on your balcony or in any outdoor space that you have that gets plenty of sun.

FAQ:

Can you grow onions in winter in Australia?

Yes, onions are a cool-season crop and will grow well throughout winter. 

How do I get my onions to grow bigger?

To encourage larger and well-formed onion bulbs, make sure that you plant them at the right time for your climatic zone and avoid feeding them with nitrogen-rich fertiliser. Also, ensure that the soil is nice and friable.

Photo of author

Annette Hird

Annette Hird is a gardening expert with many years of experience in a range of gardening related positions. She has an Associate Diploma of Applied Science in Horticulture and has worked in a variety of production nurseries, primarily as a propagator. She has also been responsible for a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.

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