Onions can make you cry but they give so much back in return. Found in almost every kitchen around Australia, they can be served hot or cold.

Choose from red, brown or white varieties as well as spring onions and shallots. Onions along with garlic, leeks and shallots are members of the Allium family.

Low in calories and full of water, they have antioxidant and anti-inflammatory properties.

Not one of the quick-growing vegies, they will take 6-8 months to harvest. They are great as a companion plant in the vegie patch, as they help to deter pests.

Follow our seven easy steps to successful onion harvest including tips along the way.

How to grow vegetables - onions
How to grow vegetables - onions

When to plant and location.

When to plant.

Onions can be grown in most parts of Australia however, they will bolt (go to seed) if planted at the wrong time of the year.

  1. In warm subtropic and tropical regions, plant seeds and seedlings from March to May.
  2. In cool and temperate regions, plant seeds and seedlings from April to September.


  • Onions like a sunny position in the garden and are frost tolerant.
  • They can also be grown in pots, just ensure they are given enough space between each seedling for proper bulb formation.


Get the soil right to harvest a bumper crop of delicious onions.

Follow our steps for easy soil preparation.

  • Onions prefer a rich, well-drained soil.
  • Pick an area in the vegie patch where a leafy crop such as lettuce, has just been harvested. This will ensure there is little nitrogen left in the soil.
  • A soil high in nitrogen will cause too much leafy growth and very little root (bulb).
  • The pH of the soil should ideally be between 6.0 and 6.5. To increase the pH add a handful of lime per square metre to the soil.
Health soil, health plants
How to grow vegetables - onions

Step 1 – Sowing Seeds.

  • Seeds can be sown directly into the ground or seed trays.
  • In the ground, scatter onion seeds or put tiny bulbs set to a deep of 0.5cm, in rows 30cm apart. Lightly cover with soil.
  • In seed trays, sow 2-3 seeds in each seed cell or scatter them to a depth of 0.5cm and lightly cover with seed raising mixture such as Seasol Seed Raising & Cutting Potting Mix.
  • Water in well with Seasol to help increase seed germination rates.

Step 2 – First growth.

  • Seeds will take 10-25 days to germinate depending on the temperature. Watch as the tiny leaves come through the soil.
  • Thin the tiny seedlings to 5cm apart when they are about 5cm high to reduce overcrowding and poor root development.
  • Use scissors or tweezers when thinning seedlings.
  • Water your tiny plants regularly and apply Seasol weekly, to help stimulate strong root development and healthy growth.

Step 3 – Baby onion seedlings.

  • Thin the onion seedlings out again 2-3 weeks later to around 10-15cms, so they are not competing for nutrients and space.
  • Keep your young seedlings moist but not wet.
  • Apply Seasol weekly to stimulate healthy growth and strong root/bulb development.
  • Apply a liquid fertiliser monthly that is low in nitrogen (less leafy growth) and higher in phosphorus and potassium (root/bulb development) such as PowerFeed PRO SERIES for Roses & Flowers.

Step 4 – Onion seedlings ready for transplant.

  • Transplant your seedling when they are around 8-10cm tall and transplant store-brought seedlings as soon as possible after purchase.
  • To plant, make a trench about 5cm deep in the soil  Lay the seedlings down with the roots in the trench spacing them 10-15cm apart, in rows 20-30cm apart.
  • Backfill with soil. The seedlings will right themselves within a couple of days.
  • Water your newly transplanted seedling in with Seasol to get them over the transplant shock.

Step 5 – Onion plant growth.

  • Watching your onions grow over the following weeks, you will see green leaf growth and the tiny bulb as they start to develop.
  • Scrape the soil away from the bulb, as it starts to form. This will help to develop a uniform bulb, that will not rot.
  • Remove weeds when they appear, as they compete for space and nutrients. Be careful not to damage onion plants.
  • Apply Seasol weekly (30mL of concentrate per 9 litres of water- standard watering can) to promote strong root/bulb development.

Step 6 – Onion bulb growth.

  • As the bulb matures and pushes through the soil, you will see flower heads appear.
  • Remove any flowers to stop the plant bolting and going to seed.
  • Do not apply mulch, as the onion bulb needs to sit above the soil not below.
  • Check soil moisture. Don’t overwater or let the soil dry out. If the soil is too wet, the bulb will rot. If the bulb is too dry, it will split and crack.
  • Apply liquid PowerFeed PRO SERIES for Roses & Flowers to help with bulb development.

Step 7 – Onion harvest.

  • When the bulbs have almost developed, the leaves will begin to fall over.
  • The plant will now divert energy away from leaf growth and into the bulb formation.
  • When the leaves have dried out and the plants are easy to pull out of the soil, the onions are ready to harvest.
  • On a sunny day, remove the soil from the onion bulbs and place them out to dry for a couple of days.
  • Cut the dried stem to about 2cm above the bulb. Store the onion in a wire or mesh bag, in a dry cool space.

Things to watch for…

  • Powdery mildew This fungal disease, can be a problem for onions. Water in the early morning to ensure the leaves dry out before the cool of the night. Remove any damaged leaves as they appear.
  • Onion thrips This is an insect that sucks the goodness out of the leaves. Treat by spraying with a hose or use an insecticidal soap.
  • Onion rot This is one of the most damaging diseases. It’s caused through soil-borne fungus Stromatinia cepivora and is virtually undetectable until it’s too late. Yellow leaves close to harvest is the first sign of the disease. There’s no cure, although prevention can be achieved through good crop rotation.
How to grow vegetables - onions
How to grow vegetables - onions

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