Every vegetable garden should have some onions. I know they are very cheap to purchase in the stores, but believe it or not, the flavor IS different. Same as potatoes, if you have never eaten a fresh, home grown potato, you just don't understand the difference in taste and texture.
Have you ever seen a seed to an onion? Tiny, tiny. If you have the time and a bit of space, it is best to sow a bunch of seeds in a good soil tray, planted only about 1/4" deep. Keep the seeds inside where it is warm, have light and moist in March & April and within a week or two you will have what looks like a small lawn. After the onions get about 3-4" tall, you can start pulling them apart and put into larger containers until ready to plant outside.
I start my first batch of onions around February/March. I purchase them either through my local gardening center-Mac's here in Gridley; or order them through a catalog-Johnny's. I prefer to start my onions by using dormant starts, also called sets. They are shipped, normally in bundles of 50-60 plants and contain normally one variety. I buy a bundle of the red, white and yellow onion sets. They look and are like tiny onions with a green stem.
The seed companies will make them available during certain months of the year. They are easier to handle, seem to have very low rate of loss, and you can space them out properly to make sure you have enough room to mature. The downside of purchasing them in bundles of sets is there is a limited variety and for small gardeners, there may be too many for you to grow. For ourselves and for our customers, we grow what most people will actually use/eat so we do not mind the limited varieties.
As these starts get going, it is important to keep weeds away from the bulb as they don't like sharing space!!! When they get about 1/3-1/2 their mature size, I make sure the soil is hand tilled around them, weed free and then I cover the roots with straw until they are finally ripe.
I like to grow for ourselves and our customers green bunching onions too, used in salads. I will start them as I stated above for the large bulb onions, but can also be purchased in garden centers in trays or 6 packs. They look like a tray of alpha growing, but you pull them apart and plant very close together. I like to stagger planting the bunching green onions so that I will have a continual supply to pull up and bundle in groups of 5-7. They last a long time in the refrigerator and a small section of the greens can be used in salads and cooking as well as the white bulb.
When the large onion bulb is ready, the green part will be dying or dead and the bulb head become raised above the ground and the outer skin will look dry. You could wash and clean it up and use it the day you pick it. But once you put water to onions, they will start to rot where you store them.
It is recommended to let them dry, with the dirt and greens on them. I bundle up a bunch of them together, rubber band them, and hang them in my shed where it is out of the sun. Some people have screens that they lay the onions on and that is great too. Last year, the family got together out in the garden and while the adults were under the umbrellas chatting, the kids were pulling up onions, comparing who had the biggest onions. Free labor!!! Afterwards, we all tied with string or rubber banded groups together and hung them up. I even braided a few.
The other day, I was cleaning out my shed to start the season and behind a shovel was a bunch of last year's onions. They were still good!!! Took them into the house and we ate them.
Don't be afraid to try growing onions. Have some fun with the green salad bunching onions too.