Onions are very popular in the home backyard garden. They are fairly easy to grow and so versatile in the kitchen. However, for success it is important to select the proper variety of onion for your area.
Types of Onions
* Common Slicing Varieties: White, Purple and Yellow, or Spanish onion
* Scallions or Green Onions: Grown for it's long stem, and little or no bulb.
* Pearl Onions or Pickling Onions
* Shallots: A mild tasting, small bulb onion popular for cooking
* Leeks: Similar to scallions, mild, yet distinctive tasting.
* Vidalia Onions - maybe the sweetest of onions - defined more by where they are grown than the variety
Long Day vs. Short Day
Most onion varieties begin to form a bulb when the temperature and hours of daylight reach certain levels. "Long Day Bulbs" begin to form a bulb, when there is 14-16 hours of daylight. They include Sweet Spanish Onions and Walla Walla onions among others.
"Short Day Bulbs" will begin to bulb when there is 12 - 14 hours of daylight hours. Short day bulbs include Yellow Granex, Texas Grano, Red Burgundy and Vidalia.
As a general guide, if you draw a horizontal line across the middle of the United States from the East coast to the West coast (see image below), every location above the line would be suitable to grow "long day onions" and the locations below the line would be suitable for "short day onions".
To illustrate the long day vs. short day trait: I once attempted to grow Vidalia onions in Sacramento, California. I was aware that commercial Vidalias are grown exclusively in the state of Georgia. However, I believed they would grow just as well in Sacramento since the summer temperature is similar. What I was not aware of was the fact that Vidalias are a "short day bulb" and Sacramento is on the border line between "long day" and "short day" locations.
The onions did grow. However, they were small and were not as sweet as Georgia Vidalias.
There are 3 choices for starting onions. Seeds, seedlings, and sets (or bulbs).
Seeds take the longest time, and should be started indoors. Onion sets are the easiest and fastest for the home gardener. They can be bought at a garden center or through mail order.
Plant onions 3 to 4 inches apart, in double rows six to ten inches apart. Leave enough room to get between the rows to weed. Onions grow best in rich soft soil or loam. But they tolerate most soils, especially if you add sufficient fertilizer. Keep the soil moist, and allow good drainage.
Green onion may be harvested anytime there is a visible plant 3 or more inches above ground. However, 7 to 10 inch tall plants are ideal. Over 12 inch tall plants, while edible, they tend to be tougher than smaller onions.
To harvest slicing (bulb) onions, pull onions after the tops turn brown and have fallen over. Rinse off dirt, and allow the onions to dry in the open air for a few days. Then, cut the tops off the onion and cut off the roots. Allow the onions to air dry for two or three more days. This will help to seal the onion and avoid pre-mature spoilage.
Most members of the onion family are resistant to insect problems. Root maggots can attack the bulbs. Tiny thrips are an occasional problem. Insecticidal soap sprays are very effective. Wet, humid weather can increase the likelihood of disease.
Onions are very hardy. Frosts, freezing temperatures, and even snow will not normally kill them. It will only slow their growth until warmer weather returns. However, extended cold below 20-25 degrees can kill onions if they are actively growing when exposed.