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Why are Vidalia onions sweet?
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Every year about this time I have someone ask me why they can’t grow sweet onions that have the same mild, sweet flavor as the Vidalia onion. 


This is not to say we cannot grow a good onion in North Georgia.  We can, but in my case, I always look forward to buying Vidalia onions.


To understand why Vidalia onions are mild and what you can do to grow a better onion is the purpose of this article. 


Flavor in onions is determined by two factors: sweetness and pungency or what we sometimes call hotness. The best sweet onion will be one that is sweet and mild (has a low pungency).


Sweetness is governed by sugar levels in the bulb.


Onions with higher sugar levels should be sweeter. Sugar levels in Vidalia onions are fairly high, but there are other onions with sugar levels as high or higher than Vidalia onions.


So why are Vidalia onions so good? It is basically because of their low levels of pungency.


In  most onions, the sweetness  of  the onion is masked by high pungency, but not in Vidalia onions.


The flavor of the Vidalia onion is a combination of low pungency levels and sufficient sugars in the onion to make it sweet.


So why are the Vidalia onions so mild?  Part of the reason is the variety of onions grown. Some onion varieties form fewer of these flavor precursors and are therefore less pungent. However, this is not the only factor affecting pungency. 


These flavor compounds are sulfur-containing compounds. The soils in the Vidalia growing area are light and sandy.


These soils do not retain sulfur and onions grown on them tend to have fewer of these pungent flavor compounds. 


The onions can be made less pungent still by careful sulfur fertilization.


Farmers cannot remove sulfur totally from their fertilization since sulfur is an essential nutrient in onion growth, but they can carefully apply sulfur so as to meet the needs of the crop for growth, while not applying so much as to make onions hot. 


Other things farmers can do to make onions less pungent is to properly apply water (especially during bulbing) and to wait until onions are mature before harvesting.


The mild climate of the Vidalia onion growing area also plays a large role in the excellent flavor of the Vidalia onion.


What does this all mean for the home gardener who has a few onions in the garden? Can they grow onions as sweet as Vidalia onions?


There are so many factors to control that it may be difficult to do this in the home garden.


However, there are a few things the home grower can do to make their onions less pungent.


1.  Do not apply complete fertilizers (10-10-10, 5-10-15, etc.) to the onions late in

the growing season.


These contain sulfur, which can make onions hotter. The complete fertilizers should be used earlier in the year and fertilizers containing nitrogen but no sulfur (calcium nitrate; sodium nitrate or Bulldog Soda; 15-0-14 and ammonium nitrate) should be used later in the year. If onions are planted in late fall and early winter, fertilize with complete fertilizers until Feb. 1 and then with the previously mentioned side-dress nitrogen compounds after that.


2. Water onions regularly after they begin to bulb.


Well-watered onions are sweeter and less pungent.


After onions begin to bulb, they can use up to one and three-quarter inches of water a week. This should be split into several applications since onion roots are shallow.


Apply one-half to three-quarter inch at each application.


3. Do not harvest onions until about 25 percent of the tops have fallen over.


Early harvested onions are more pungent and will not store well. Pull onions and clip tops off (do not pull them off).


Let onions dry in a shady, dry spot until necks are fully dry and then store in a cool, dry spot. In a dry, air conditioned room; onions can store up to three or four months or more.


Try to store in a spot where onions will have plenty of air movement around them.


Be careful during harvest and drying not to damage onions. Cuts and bruises provide places where rots may begin.


Clark Beusse is the Dawson County extension agent.