Tips & Techniques for Growing Onions
Varieties of Onions
Onions are grown to eat as scallions or onion heads.  There are bunching varieties for eating as scallions that don't form heads.  The ones that grow heads can be sweet or hot.  Onion heads can be oval or round and white, yellow or purple in color.   A popular sweet variety is the Walla Walla which is similar to the Vidalia onions grown in southeast Georgia.  They say that the Vidalia onions are so sweet that they can be eaten like an apple.  A combination of several factors including the climate and sandy soil are believed to be responsible for their unusual qualities.  Some varieties of onions keep better in storage than others.  Shallots and leeks (also called flags) are in the onion family but are different.  Shallots are smaller than onions and form clusters of small mild tasting heads while leeks can grow taller and have flat leaves which are best eaten in soup.  
Preparing the Soil
Rich sandy soil is best for onions.  Select a sandy location for the onion rows which will not be next to your peas or beans.  If no part of your garden is sandy, you may want to till in some compost to keep the soil loose enough for heads to form.  Preparing the soil to plant onions is simple.   You just need to till the garden and mark off rows.  Since pollination is not a concern, one can have just one row or several.  A string with a stick tied to each end can be used for marking off straight rows.  Using the sticks, measure and mark the location of each row.  Space them to allow best use of your tiller.  Using a hoe, make a straight trench about 4 inches deep beneath the string.  Once a trench has been made, you will be able to plant the onion sets or plants directly in the trench without any additional preparation.
Planting Onions
Onions can be planted using sets or plants.  Sets are readily available in the spring at a lot of locations including some grocery stores.  You may want to plant your onions too thick and thin them by pulling onions to eat as scallions.  If so, you can place onions sets about every inch apart within the trench and completely cover them with soil.  It is best to place them with the root end down.  Plant them so thick will make weeding more difficult but you have the added benefit of fresh onions. 
Weeding & Plant Maintenance
By planting onions in rows, yon can remove most weeds by tilling close to the plants.  If you planted your onions close together, you will have to pull most of the weeds that are in the rows.  You should till and hoe about three times during the growing season.  After the onions are thinned, you can hoe out the few weeds that come up late.  It is important to keep weeding them until the heads have formed. The plants should grow fast once the weather turns warm.
Controlling Diseases and Insects
Onions can usually be grown without too many problems with diseases or pests. The pests and diseases that are a problem mostly attack the bulbs.  The most common pests are cutworms and root maggots.  The worst disease seems to be root rot.  This can be controlled to some extent by crop rotation and removing the onions as soon as they are mature.  If you find that a fungicide or insecticide is needed, make sure you pick one for the specific problem and that can be used on garden vegetables.  Always read and follow the directions on the containers when applying chemicals on garden plants. For specific details on controlling diseases and pests, click on the "Gardening Resources" tab and go to the Sources of Information on Vegetable Garden Diseases and Pests.
Once the tops start to die, the onions are ready to be pulled. You will need to break off the tops and lay them out in the sun to dry for a few days before storing them.  It is possible to keep onions for months, if stored in a cool dark place.  Light and warmth can cause stored onions to sprout and rot. Onions are mostly eaten fresh or cooked.  Their flavor changes and aren't very tasty canned or frozen.