There are many different varieties of onion however in general they all want the same things in order to grow well. All they need is the right climate, soil and just enough water to grow to their full potential.
They are a great staple food to have on hand. Onions are used in a multitude of recipes, from soups and bakes to salads and breads. Plus, if you by chance have excess, they are one of those remarkable foods that you can pickle or dry to store long term.
Temperatures
Onions grow best during colder months, especially during the earlier phases of growth. Once they start to mature some slightly warmer days would be ideal, so planting later in the winter is a good idea.
Optimal temperatures for growth are 10°C to 20°C, although on average they are happy in temperatures between 7°C and 29°C.
Another bonus that makes onions an easier crop to grow is that they are frost tolerant.
Sun
Your onions want as much sun as possible. These cooler-weather vegetables would be happiest with 10 to 14 hours of sunlight per day, so plant them somewhere with full sun. Even avoid planting them where they may be in the shade of another plant.
Water
Onions need a lot of water for optimal growth. So ideally your soil should be kept moist almost all of the time, however, it should never get soggy or soaked. If the ground is too wet all the time the risk of fungus growth is increased. Plus, overwatered onions could lose much of their flavour.
When watering try not to wash soil away from the plant and expose any part of the roots.
Soil
Similar to most winter crops that want a fair amount of water, onions need well-drained and loose soil. Also, fertile, nitrogen-rich soil is ideal but not absolutely necessary, and with regards to the pH, your onions would prefer soil that is between 6.2 and 6.8.
Space
The space requirements will vary depending on the type of onion as well as when you plan to harvest them. For example, should you wish to harvest a little early to access smaller green onions, you will only need to grow your plants about seven to 10 centimetres apart.
Assuming you are growing the average large white onion to full maturity, you will need to plant each one between 10 and 15 centimetres apart. When sewing seeds, plant each one about two centimetres deep.