Onions: a growing guide

If you want to grow your own bulb onions, the keys to success are choosing the right variety and planting at the right time.

Harvest: lifting a crop of onions

If you want to grow your own bulb onions, the keys to success are choosing the right variety and planting at the right time. In most parts of Australia, that’s autumn and winter, although in cool zones you can also plant in spring. In the tropics, don’t even attempt them; in subtropical areas they can be challenging. Most commercial production is in South Australia and Tasmania and we consume an average of 8kg per person a year.

We think about onions as being brown, white or red, but in terms of growing them, the critical difference is the number of daylight hours each variety needs to develop a fat bulb before harvesting. Onions take about six months to mature and most are harvested in summer and autumn.

Early season – also called “short day” – varieties need 10-11 hours of daylight. They’re often a bit quicker from planting to harvest but don’t store as long as other types. Late season or long day varieties need 15-16 hours of daylight; they take the longest to mature and are the best keepers. Mid-season or intermediate varieties are somewhere in the middle. Eschalots or French shallots that produce a cluster of golden bulbs, rather than one large one, are intermediate-day bulbs. There are a few day-neutral varieties and these are best for more northern areas where you don’t get the distinct seasons and long summer days that you do in the south.

Onions need a sunny spot and fertile, free-draining soil with a pH of at least 6.5. Add lime or dolomite if your soil is acidic. They have a high demand for potassium, but too much nitrogen can stop bulbs forming. Prepare the bed a few weeks before planting, then choose either seeds or seedlings. Keep young plantings weed-free. As the bulbs form with the onset of spring, they pull themselves up to the surface of the soil. They’re ready to harvest when the leaves are dying down. Lift them in dry weather and allow to harden off in the sun for a few days before storing. If you want to collect seeds, leave them until the second year when they’ll produce flowers and set seed.

If bulb onions sound too challenging, stick with their relatives, called green onions, such as leeks, spring onions and shallots/scallions, which form a thickened leaf base rather than a true bulb and are much easier to grow; they’re not sensitive to day length. Leeks grow in most climates and take 18-25 weeks to mature; in warm areas plant in autumn and winter. Spring onions grow all year and are suited to warmer climates and pots.

Good to know

The fresh green tops of bulb onions are edible

The papery outer skins are used for fabric dyes

Stinging, teary eyes when cutting onions are caused by the sulfur compounds. Try chilling the onions first, use a sharp knife and leave the root end intact until last

Onions have been cultivated for more than 5000 years

Q&A

After a long, hot summer my two-year-old peach tree looked dead. Now some suckers have appeared so all may not be lost. Should I prune? Angus McFarlane, Perth

Your peach was almost certainly grafted, which means any suckers from the roots or below the graft will not be the variety you purchased. Rootstocks are selected for vigour, resistance to root-knot nematode and tolerance of poor soils, not for their fruit. You need to completely remove this tree and plant a new one.

Crows have moved in to our suburb, destroying other birdlife. How can we deter them? Diane Barrington, Gold Coast

Crows have long had a tarnished reputation. Populations have steadily increased in urban areas because these highly intelligent and omnivorous birds exploit human-made food resources. But a Brisbane study found the local crow species showed lower levels of nest predation than butcher birds, pied currawongs, noisy miners and grey shrike-thrushes. Measures to reduce access to food waste need to be community-wide. Bird-scaring devices can disperse communal roosts if they’re a significant nuisance or health hazard.

I’d like to plant out a bamboo that was given to me in a pot, with no label. How can I be sure it’s not an invasive type? Valerie Taylor, Mandurah, WA

You need expert identification to be certain, as clumping types are the only ones that should be planted out. Bamboo Landscape Plants at Wattleup (bamboowa.com.au) offers this and is not too far from you.

The gardening prize

Send your questions to: [e-mail] or Helen Young, PO Box 3098, Willoughby North, NSW 2068. Website: helenyoung.com.au. The best question for May wins two boxes of 10 Wallgarden modules giving 2 sqm of planting space, worth $190. wallgarden.com.au