You can grow onions from seeds, smaller bulbs or transplant.
If you are planning to start with the seeds, it is better to first grow the seedlings indoors. Use special seedling trays (or can alternatively opt for used Egg cartons) and good quality potting soil.
If you are planning to buy transplants from the market, talk to your nearest garden or nursery shop. Though in transplant, the choice of variety is limited, the survival chances are pretty high.
You can also grow onions from immature bulbs. The best part of choosing bulb is that it is easy to plant, less disease prone and earliest to harvest. Choose bulbs which are smaller in size (diameter less than ½ inches). The big sized bulbs are much more prone to bolting.
Raised garden beds are a very good option for growing onions. It provides warm soil and ideal air circulation to the plant. The ideal pH range is from 6 to 7. If your soil is not in this range you can make it to that region by adding Limestone (if your soil pH is lesser than that), or Peat moss (if your soil pH is greater than that).
Adding sufficient amount of compost also help in reducing the pH of the soil as well as provide the nutrient to the plant.Whatever you do make sure the soil have a very good drainage. Good soil drainage is compulsory for growing onions.
Plant them 4” apart. It will make the onions to mature fully. In case you are planning to harvest green onions (scallions), you can leave a smaller space (2”).
Pull or dig the onions out. After that, leave them in the open sun for two days to dry. This will help prevent rotting.
After drying, the skin of the onion will have a uniform texture. Now it is time trim the roots and detach the stem from the bulb. Remove any soil that is present in the skin.