How to Grow Onions
When it comes to growing Onions in the vegetable garden, a decision is usually made depending on available space. Spring Onions, like garlic are grouped with root vegetable as they do not require large amounts of fertiliser. The fertiliser levels in the soil are not as critical however as when planting bulb onions as the entire plant is used. Spring onions can be planted from either seed or seedling. I prefer seedlings as they are just easy to handle and relatively cheap to buy. Because they are harvested relatively early, they don't require a lot of space in the vegetable bed.
Typically when you buy seedlings, you will often find the roots of the plants heavily intertwined and care must be taken to not cause too much damage when separating them. Create a drill in the garden bed, with the cleared soil mounded along the drill on one side. Remove the plastic punnet carefully and soak the seedlings in a container of water to help remove the soil and gently separate the plants from each other. Lay the seedlings one at a time in the drill, with the roots in the bottom, leaning the plant on the side opposite the soil mound. Space seedlings about 5-10 cm apart, then when done, gently push the mounded soil from the drill back in to cover the roots. There is no need to worry about the seedlings laying over. Within a few days, they will stand themselves upright. Gently water in with a watering can or wand on your hose. I recommend using a seaweed concentrate.
Bulb onions are the loosely grouped onions that most people are familiar with. These are usually either white, red or brown skinned. Generally, they take up more vegetable garden bed space, for a longer period as they need more room to srpead as the bulb develops and time for this to occur. If you have limited space, they may not be a practical home vegetable garden crop.
Typically brown onions are best suited to keeping when harvested and last longer than the others when properly stored. Personally I have had a real hit and miss experience with onions. Why? Well onions are daylight sensitive in their growing habits and different varieties are suited to different planting times. Basically, onions are affected by the number of total hours of daylight in their growing time. If planted at the wrong time, they can receive too much daylight and bolt to seed. My success story has been "potato onions".
Potato Onions are a clumping variety that grow from one a saved bulb. Each bulb as it grows divides into multiple bulbs. They are not generally grown from seed. Each year I save somewhere between 12 and 20 bulbs and replant them. The onions basically range from small (about the typical size of a pickled onion) to a small bulb onion. Being small you have to use more of them, but they are quite strong flavoured and are very prolific growers, producing many kilos from only a small initial planting.
Red, White and Brown onions, like all root vegetables are best grown from seed as they are less likely to bolt to seed than if grown from seedlings that have had their roots disturbed when planted out. Red Onions, often referred to as salad onions have the same requirements as white and brown. If you are purchasing seedlings, I personally have found the seedling punnet labels to be somewhat generic and not specific enough. Have a look at the planting instructions on the equivalent seed packet to get the right information suitable to your area. Follow the same process for planting bulb onions in your vegetable garden as described above under "Spring Onions".
White onions are often less pungent than brown onions and do not store as well or for as long as brown onions and are therefore better suited to harvesting through the summer period, where the brown onions are still growing and increasing their bulb size before dying down. If planting seedlings refer to the instructions for Spring Onions or follow the instructions on the packet if planting seeds. Brown onions, the best keepers for use in the winter period have the same growing needs as those above.I'm lucky enough to have have plenty of space, so I dedicate one entire vegetable garden bed to growing both my bulb onions and spring onions together.
Position: Full Sun to partial shade
Plant: Sow direct as seed and thin to distances of around 10-15cm as plants emerge and grow or, plant out seedlings following the drill method described under spring onions.
Frost Tolerant: Yes Heat tolerant: Yes
Feeding: Like well composted soils, but low in nitrogen other excess leaf growth will occur at the expense of bulb development.
Planting group: Allium, so grow with other root crops
Pests: Birds, slugs and snails as seedlings, otherwise few problems.
Harvesting: Depends on variety, but harvest when at a reasonable size. If Onions are to be stored, leave them until the tops yellow and die.