Growing Onion in Australia: The Complete Guide

Onion is an easy to moderate bulb & allium to grow, needing full sun with regular, taper before harvest watering.

We get asked about onion often enough that it's worth setting out the full picture here, beyond what fits on our printable card.

It's worth being clear about why onion is worth the bed space before getting into how to grow it. At a glance, it's rated easy to moderate, with a sun of full sun; water of regular, taper before harvest; soil ph of 6.0–7.0 — details that matter more once you're actually planning around them than they do on a first read. The rest of this article works through exactly what each of those means day to day, in more depth than a single printable card has room for, and with the reasoning behind each recommendation rather than just the recommendation itself.

Climate and Timing Considerations

Australia's climate zones change growing timing more than most general advice accounts for. Cool temperate zones (Tasmania, the Victorian highlands, southern NSW) have recurring frost risk well into what other zones call spring, which compresses the safe planting window for frost-tender plantings. Warm temperate zones (Sydney, Adelaide, Melbourne, Perth) sit closest to what general advice assumes by default. Subtropical zones (Brisbane, northern NSW) rarely see frost at all, and the growing calendar shifts earlier and later as a result. Our site-wide zone setting adjusts the advisory note shown on the Planting Calendar for exactly this reason — worth setting once if you haven't already. The same zone setting also feeds the Harvest Calendar, so both ends of the growing cycle reflect wherever you actually garden, rather than a generic Australia-wide average.

• Cool Temperate (TAS, VIC highlands, southern NSW, ACT): shorter frost-free window — lean toward the later end of any spring planting window shown on the guide above.
• Warm Temperate (Sydney, Adelaide, Melbourne, Perth, coastal NSW/WA): closest match to the general timing shown above; frost is occasional but rarely severe.
• Subtropical (Brisbane, northern NSW, coastal QLD): minimal frost risk — often plantable a few weeks earlier and later than the general window shown above.

Day-length matters

Onions form bulbs in response to day length — short-day varieties for warmer zones, long-day for cooler ones. Getting this wrong means small or no bulbs.

Planting Onion

Method. Sow seed or plant seedlings shallowly; choose a variety suited to your day length.

Soil. Loose, well-drained, weed-free.

Timing. Sow or plant in autumn to late winter depending on zone and variety.

Taken together, these are the details that separate a smooth result from a frustrating one.

Ongoing Care

Worth paying attention to:

• Keep beds weed-free — onions compete poorly with weeds.
• Water regularly, then stop 2–3 weeks before harvest.
• Feed lightly early on; avoid nitrogen once bulbing starts.
• Bend tops over gently once bulbing is well underway.

Getting these details right matters more than it might seem — keep beds weed-free — onions compete poorly with weeds. Bend tops over gently once bulbing is well underway. Treat this list as a routine to build rather than a one-off checklist, and it becomes second nature within a season or two.

Problems to Watch For

Keep these points in mind:

• Onion thrips — silvery leaf streaking; blast off with water, encourage predators.
• White rot — soil-borne; rotate beds for years if it appears.
• Bolting — cold snap after planting; plant at the right time for your zone.
• Splitting bulbs — inconsistent watering.

Each of these compounds over a season — small misses early tend to show up later — onion thrips — silvery leaf streaking; blast off with water, encourage predators. Splitting bulbs — inconsistent watering. Treat this list as a routine to build rather than a one-off checklist, and it becomes second nature within a season or two.

When and How to Harvest

Signs. Tops yellow and fall over, necks soften.

Method. Lift with a fork once most tops have fallen.

Curing. Cure 2–3 weeks in a warm, airy, shaded spot until necks are papery.

Storage. Cool, dark, ventilated. Keeps 4–8 months.

It's worth reading these as a set rather than in isolation; they reinforce each other.

Preserving. See Root Cellaring for curing and storing alliums beyond the basics above.

Recipes. Try our Caramelised Onion - a way to use a glut.

Companions & rotation

Our printable card above lists specific plants that pair well nearby and others best avoided, along with a rotation note: Carrot, Beetroot, Brassicas, Lettuce, Beans, Peas. Getting this right matters more over multiple seasons than it does in any single one — the benefits and the risks of poor rotation both compound over time rather than showing up immediately.

Related Guides

If onion suits your garden, these related guides in the same category are worth a look too:

• Elephant Garlic
• Garlic
• Leek
• Shallot

For the condensed, printable version of everything above, head to the main onion guide page. Companion planting and bed rotation both make a measurable difference over a season, and our Companion Planting Checker takes the guesswork out of both. As with every guide on this site, this is general information based on our own research and experience, not professional advice — your specific soil, climate, and circumstances will always vary from ours to some degree.

Beyond the printable card, our Planting Calendar and Harvest Calendar tools will show a zone-adjusted note for onion specifically, and the Companion Planting Checker covers the specific pairings mentioned above in more detail.

Frequently Asked Questions

→ View the printable A4 guide for onion