The onion is a member of Allium, with the globe-type garden onion as Allium cepa, and the bunching-type (“green onion”) as Allium fistulosum. The onion plant of the globe-type has hollow, bluish-green leaves that grow alternately in a fan-shaped swath, and that are fleshy, hollow and cylindrical, with one flattened side. The bulb at the base of the plant begins to swell to its globe shape as it matures. In autumn, the foliage dies down and the outer layers of the bulb become dry and brittle. The crop is harvested and dried, and the onions are ready for use or storage. Take note that onions can be attacked by several pests and diseases – particularly the onion fly, the onion eelworm and various fungi that cause rotting – but there are remedies if used early on before the plants are damaged too much.
Bunching-type onions are very similar in all aspects to the globe-type except they don’t actually form a true bulb, and they are harvested in the cooler months for their long green tops that are attached to the tiny, pungent, white “nub”.
Growing onions from seed can be much more rewarding than planting onion sets. Sets will produce a faster harvest; but, there are significantly less varieties available for sets, and the harvest of sets tends to be smaller, more susceptible to disease, and the crop from sets does not store as well as onions grown from seed.
Onion seeds perform best when started indoors to be transplanted in the garden when the seedlings are between 4 to 6 inches tall. Place the young seedlings in light to medium soil – preferably with a pH of 6.0 to 7.5 – that has very good drainage. Globe-type onions begin to form their bulb when the temperature and the number of daylight hours are optimum, and those two factors occur much differently in northen climates as opposed to southern areas. As a result, “Long-day” varieties are recommended in the Northern U.S. while “Short-day” onions should be grown in the South.
1. "Long-day" onions produce bulbs only when days reach 15 or more hours of daylight. In the Northern U.S., winter days are very short; conversely, summer days are longer than in the South. (Daylight length varies greatly as you get farther and farther away from the equator.) Long-day onions have a chance to produce enough top growth in the spring before the day length triggers bulbing – and the more top growth, then the larger the resulting onion. If short-day onions were grown in the North, the onions would “bulb-up” too early and would be small by comparison.
2. "Short-day” onions are grown in the South where the bulbs begin forming after daylight reaches about 10 to 11 hours. They are typically planted in the fall in order to grow through the cooler months, and bulb formation will then begin when the following summer days get longer. If long-day onions were planted in the South, they may not experience enough day length to ever trigger the bulbing process.
3. "Intermediate-day" types require 12 to 13 hours of daylight to stimulate bulb formation. They grow best in the transitional climates.
Most onion cultivars are about 89% water, 4% sugar, 1% protein, 2% fiber and 4% other. They are high in vitamin C, vitamin B6, and folic acid, plus they are very low in fats and in sodium. Onions (as mature bulbs) are normally available in three colors – Yellow, Red, and White; while Green Onions are used differently.
1. Yellow onions, also called brown onions, are full-flavored and are the onions of choice for everyday use. Yellow onions turn a rich, dark brown when caramelized and give French onion soup its sweet flavor.
2. Red onions are a good choice for fresh use to liven a dish or sandwich with color. They are also great for grilling and char-broiling.
3. White onions are the traditional choice to use in classic Mexican cuisine. They have a golden color when cooked and a particularly sweet flavor when sautéed.
4. Green onions is a term used for any globe onion harvested for its long green tops attached to the immature bulb during the cooler, early part of the gardening season so as to be eaten fresh. Bunching onions – without a true bulb – are also called Green onions since they are grown solely for their fresh use as green tops attached to white nubs.