Onions are a common resident of most Aussie pantries. But it may not be worth your while growing them. Onions are very cheap to buy, whilst other crops which have the same garden benefits like garlic are more expensive. In saying that I generally always have a few red onions in the garden so I always have one to hand.
Make sure you choose a variety which is suited to a cool climate as not all are. Creamgold is the best for cool zones and is very similar to the typical store bought brown onion (if not the same). Spanish or red onions also do well in a cool climate.
I generally advise to plant all root crops from seeds straight in the ground. This is because they can be disturbed when transplanted from a seedling tray to the garden. This isn't quite the same for onions, but I would still recommend starting from seed.
If you do buy seedlings, you plant them by lying them down. So dig a trench, and place the onion roots in the trench lying them perpendicular to the trench. Cover their roots and water. They will stand up themselves.
You can also grow an onion from a store bought onion. Cut the dry roots off the base of the onion. You don't need much of the actual onion so just cut the roots off as you usually would when cooking. Float the roots in water until new little white roots have sprouted. Make sure you refresh the water daily. This will take a few days depending on how warm it is. Once roots have sprouted plant in the ground and keep moist. The top will shoot a little green leaf. If this doesn't happen then it was unfortunately a failed attempt. I have about a 50% success rate but keeping them watered after planting out is key. Each replanted onion will regrow 2 - 5 new onions. I grow all my onions this way, by replanting all onions I have harvested.
If you have any onions in your pantry which sprout green shoots, you can remove these and plant them straight in the ground. Free onions!
Onions are planted in February and harvested as you need in spring. I let one or two go to seed but I've never had any success with them growing from self seeded seed. It may be the seeds are blown too far away. You can dry and store onions. Making an onion rope is a common way to store them.
I always plant my onions as a border crop. They are great at deterring pests from entering your plots.
Onions can be grown in containers but their bulbs are often smaller so space them thoughtfully. If you only have a container as an option then go ahead, but otherwise the ground is best.
Space them about 10cm apart. This will result in a dense row but it is the best use of space. The seeds are quite small but it is possible to space them out as seeds, or you can simply thin out the seedlings once they have sprouted. I do the later.
Onions are a 7 - 9 month crop depending on variety, weather and what size you choose to harvest. It's for this reason that I suggest you consider the value of planting veruses garlic or leeks which are a more expensive crop to buy. They will sit on top of the soil, and no under it.
Pull them out of the ground and dry, leaves and all, before storing.
Onions are a great pest deterrent and are best used as a border crop. This also makes it easier to keep away from plants they don't get along with.
Plant with lettuce and tomatoes. Chamomile apparently improved an onions flavour. Legumes, sage and asparagus do not like being planted near onions.
In the crop rotation cycle onions are a root vegetable. In some crop rotation plans onions and the rest of the allium family are planted separately after leaves and before roots. But I plant mine as a border plant with other root crops.
Onions are not suitable for succession planting because they take so long to grow and are planted at a specific time of year. But they store well so having 100 onions ready at once isn't really a problem.
Include onions in your regular seaweed, magnesium and calcium watering routines.