How to Plant, Grow & Harvest Onions in 5 Easy Steps

How to Grow Onion

The basis of so many delicious dishes, onions (Allium cepa) are an essential ingredient in every cook’s store cupboard. With so many tasty types of onions available, why not grow your own and try some of them out? Follow our simple guide to growing onions.

Planting and harvesting onions in Australia

Plant onions in early to mid spring in most climates. In warm climates, plant onions in autumn.

Harvest onions between summer and autumn in most climates. In warm climates, harvest onions in late spring.

The best onion types to plant

With so many types of onions available, it can be difficult to choose which one to grow! Here are a few of our favourites:

Onion ’Gladalan Brown’: a large early cropping, brown-skinned heirloom variety; very reliable.
Onion ’Gladaland White’: an heirloom medium to large white onion.
Onion ’Ailsa Craig’: mild tasting, straw-yellow coloured, large Spanish type.
Onion ’Long Tropea Red’: purple or red heritage variety with mild, sweet flavour
Onion ’Odourless’: pale brown skin and mild flavour; has no smell.
Creole
Transylvanian

Essential equipment for growing onions

To grow onions at home, you will need:

Onion ‘sets’ (young onion bulbs) or seedlings
Spade
Fork
Supply of Scotts Osmocote® Compost Premium Soil Improver
Scotts Osmocote® Controlled Release Fertiliser: Tomato, Vegetable & Herb
Scotts Osmocote® Plus Organics Tomato, Vegetable & Herb Potting Mix
Netting

When to plant onions in Australia

Some onion varieties can be planted in autumn for an early summer harvest, but there is a chance the bulbs may rot in heavy soils that remain wet over the colder months. The best time to plant onion sets is in early to mid-spring.

Onions need rich, fertile pH neutral or mildly alkaline (6.5 to 7.5) soil in full sun. To prepare the soil for spring planting, dig in lots of Scotts Osmocote® Plus Organics Tomato, Vegetable & Herb Potting Mix, Scotts Osmocote® Compost Premium Soil Improver or well weathered animal manure in autumn and leave it to settle over winter.

growing onions

How to plant onions

Although you can grow onions from seed, it’s simpler to grow them from ‘sets’. Sets are young onion bulbs, grown especially for planting.

Before planting onions in spring, dig over the plot to break up the soil and clearing it of all weeds. Tread down the soil to lightly compact it and rake over to produce a level surface with a light, crumbly texture.
A couple of weeks before planting your onions, rake in a Scotts Osmocote® Controlled Release Fertiliser: Tomato, Vegetable & Herb at the rate recommended on the bag or container.
Plant onion sets 20cm apart, with the tips of the young bulbs just showing above the soil. Follow label instructions for planting seedlings. Allow 30cm between rows.
Water in after planting – this helps to settle the soil around the new plants.
Cover the area with netting to stop birds pulling up the young plants.

How to take care of onion plants

Follow these tips for a good onion harvest:

Keep the plot weed-free. Hoeing between rows risks damaging foliage and bulb tips, so weed by hand where possible.
Water regularly in dry periods.
Remove any flower spikes as soon as they appear.
Stop watering once the leaves start yellowing – this means that the bulbs are starting to swell.

How to harvest onions

Spring-planted onions should be ready to harvest in late summer and early autumn. In warmer areas, autumn-planted onions will be ready to harvest from early to mid-summer. Once the foliage starts to yellow and bend over, the bulbs are ready to harvest. Use a fork to carefully lift them, taking care not to penetrate or bruise the bulbs.

Storing onions

Place the bulbs in a single layer on a drying rack or on a slatted shelf that allows air to circulate around them.
Leave them outside in the sun or under a patio or veranda roof for a couple of weeks to dry.
Once the skins are dry and papery, store the bulbs in net bags or plait the foliage to form bundles.
4. Store in a light, cool and well-ventilated spot. Bulbs stored in the dark are more likely to sprout.

Common onion pests and diseases

Onions bolting	Bolting occurs when onions stop developing their bulbs and instead produce flowers. It can be triggered by stress, such as sudden dry period or cold snaps. Onions that have bolted can’t be stored but are still edible. Choose varieties that have been heat-treated to reduce the risk of bolting, or look for bolt-resistant varieties. Cover plants with fleece to protect them against sudden cold snaps in spring. Water plants regularly in hot, dry periods.
Onion white rot	Onion white rot is a soil-born fungus that causes leaves to yellow and wilt, and bulbs to rot. No chemical controls are available. Avoid planting onions in soil where this has previously been a problem.
Leek rust	Leek rust is a fungal disease which can affect all alliums. It appears as orange spots on leaves. and is more likely in wet conditions. Heavy infections can affect yield. Space plants well to ensure good air circulation. Remove and destroy any affected leaves. Don't plant onions in soil where this has previously been a problem.

Onions bolting

Bolting occurs when onions stop developing their bulbs and instead produce flowers. It can be triggered by stress, such as sudden dry period or cold snaps. Onions that have bolted can’t be stored but are still edible.

Choose varieties that have been heat-treated to reduce the risk of bolting, or look for bolt-resistant varieties.
Cover plants with fleece to protect them against sudden cold snaps in spring.
Water plants regularly in hot, dry periods.

Onion white rot

Onion white rot is a soil-born fungus that causes leaves to yellow and wilt, and bulbs to rot.

No chemical controls are available.
Avoid planting onions in soil where this has previously been a problem.

Leek rust

Leek rust is a fungal disease which can affect all alliums. It appears as orange spots on leaves. and is more likely in wet conditions. Heavy infections can affect yield.