The flavors of onions are very dependent upon onion type, and chefs usually use several types of onion in their cuisine. Most modern hybrid plants are designed to look nice and keep well, but not necessarily for flavor. Some of the better flavored onions are the heirloom varieties, or old fashioned varieties. There are also many varieties worldwide, and these international varieties often have high flavor. Flavor will be improved when the onions are allowed to mature in the media.
Onions hold their flavor through storage if they are poperly dried.
Nutrients also affect flavor, and at this point you can experiment to find the best flavor recipes for onions. Nutrient can be reduced a few days before the final onions are harvested. Trace mineral supplements should be added to the water of the onions as they ripen. The flavor could be flat because of a high pH in the water. We add vinegar to the onion water to keep the pH at about 6.0 to 6.2.