By Kate Torpie, Garden Guides Contributor

About Onions

Onion, or Allium cepa, is a cool weather vegetable that is easy to cultivate. Its scent belies the fact that it is a member of the lily family (and therefore toxic to many house pets). Brave people eat onions like apples: just biting right into them. The rest of us may enjoy onion in soups, salads, grilled over steaks or minced into a hearty red sauce. Onions are either short-day and long-day onions. Onion plants form a top first, and then begin to sprout a bulb. Long-day onions will begin to form a bulb during seasons when there are about 15 hours of daylight; short day onions will do so when the days have only 10 hours of sunlight.

Site Preparation

If you are transplanting onions, make sure you keep your plants dry and cool until you are ready to plant them. You can keep them for about 2 to 3 weeks before they die. To prepare your soil, make a raised bed (about 4 inches) that is about 20 inches wide. You are lucky if you live in an area with rich, loamy soil. If not, buy a good fertilizer because onions require fertile, basic soil. Use about ¼ cup of fertilizer for every 5-foot row of onion plants. Then cover the fertilizer with another 2 inches of soil. An ideal site allows you to make rows in the direction of the prevailing winds in your area. This will prevent moisture from sitting in the soil too long, which can cause disease. Avoid objects that may block a breeze (such as buildings or trees).


When you should plant onions depends on where you live and how many hours of daylight you receive during the various seasons. You will also consider the types of onions that you are planting. Transplanted onion plants will produce the largest onions, provided that you care them for them successfully. However, you can also buy grow onions from sets. Sets are the simplest method and can even be used if you have a window box or indoor herb garden. These onions are smaller and moister, and they aren't as easy to slice. But they are perfect if you want "green onions," as smaller baby onions are called. If you are going to harvest green onions, place the larger of the sets within touching distance of each other. To produce dry (large, the kind you see at a grocery store) onions, place the transplants about 4 to 6 inches apart. Whichever type you are planting, set them 1 inch deep. As mentioned previously, use starter fertilizer if your ground is not rich in nutrients. Tip: you'll know you planted your onions too late in the season if they sprout a white onion flower, and this will result in a smaller bulb next year.


Weather you plant transplants or seedlings from a set, the best idea for weed control is to apply a pre-emergent herbicide. After planning, the only good way to clean out weeds is by hand. But avoid being too vigorous: you don't want to damage the bulb. Onions fall prey to fungi. Blight and purple blotch are 2 such diseases. With the first, the leaves will turn yellow. With the latter, they develop holes that are lined in purple. Since moisture and rain exacerbates these conditions, choose a site where wind can get to the plants and help dry them. When you plant the onions, you will use fertilizer. Apply more fertilizer every 2 to 3 weeks after that. Immediately water the soil once you've put down the fertilizer. Pay close attention to the stems of the onion; once it feels soft and looks a bit droopy, you can stop using fertilizer. This is also a sign that you will be able to harvest your dry onions in about 4 weeks!

Harvesting and Storage

Pick your onions in the morning. Once the stems fall over, onions are ready to be harvested. Just to be sure, stalks should be 6 inches tall. The taller the stalk, the stronger the flavor. Green onions with tall stalks will most likely be way too strong to eat raw, but they can certainly be used for cooking. If you choose to store your onions, you must make sure they are thoroughly dry before storing. Once you pick the bulb, leave it outdoors until the late afternoon. Make sure you do not leave them in the bright sun, or they will burn. Also be sure that you bring them inside before the gloaming and dewfall. You don't want moist onions or they will rot. It is equally important to keep them from bruising while stored. One of the easiest (and best) ways to store onions is to place them in a nylon stocking. Tie a plastic tie between each onion (or put a sock between each). Hang the stocking in a cool, dry place. This way, dry onions will last about 1 year. Green onions will not last as long. Another tip: the sweeter the flavor of onion, the shorter it stays good. The point brings us to varieties,there are a lot.

Choosing a Variety

If you are going to get a set, your choices are usually limited to color: yellow, white or red. Red are the sweetest, and yellow are the most pungent. If you are going to transplant your onions, you should ask at your local garden center which varieties are the hardiest in your area. For example, White Sweet Spanish onions are best in areas where long-day onions will thrive (such as in the southern states). Bermuda onions are better where the days are often short.

Special Features

Onions are high in energy and antioxidants. They increase circulation and lower blood pressure. They contain vitamins B1 and B6. Onions make you cry because when the cellulose is damaged upon cutting, a chemical compound is released. The compound turns to sulfuric acid when it comes into contact with water. Try putting your onions in the refrigerator before cutting. The cold keeps the chemical contact from rising, and it is less likely to reach your moist little eyeballs.

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