Keep your onions free from weeds.
Onion is a cool-season vegetable that can be grown successfully throughout most of temperate North America. Onions may be grown from sets, transplants, or seeds.
Onions start bulb formation when the day length is of the proper duration and different varieties of onions require different day lengths to initiate bulbing.
In general, most common varieties fall into one of two classes, long-day (for northern latitudes) and short-day (for southern latitudes). For this reason, onion varieties that are grown in the South are not adaptable to the North and vice versa. Late plantings of the suggested varieties also result in small bulbs or lack of bulbing altogether in any location.
High temperatures and low humidity are advantageous during bulbing and curing. Onions have shallow roots and compete poorly with weeds and grasses. Timely shallow hoeing and cultivation are important, especially when the onions are small.
Onions may be eaten raw, broiled, boiled, baked, creamed, steamed, fried, French fried, and pickled. They are commonly used in soups, stews, stir-fries, and in combination with most vegetables and meats.
Growing Onions From Sets
Growing green onions from sets is probably the simplest method for the home gardener. The plants are quickly established and become vigorous and strong. Onion sets may be used to produce both green onions and dry onion bulbs, though production of really premium dry onions requires methods described in the following section.
Several varieties are used for onion sets. All of these varieties are widely adaptable. The home gardener has little choice of varieties at the store, however, because sets are seldom sold under varietal names, merely by color: yellow, white, or red.
- Purchase firm, dormant sets early - before they begin growth in heated salesrooms.
- Store sets in a cool, dry, dark environment if planting must be delayed after purchase.
- Divide the sets into two sizes before planting. Large sets (larger than a dime in diameter) are best used for green onions.
- If allowed to grow, these sets may "bolt" and form flower stalks.
- The small sets (smaller than a dime in diameter) produce the best bulbs for large, dry onions; and they usually do not "bolt."
- Extremely cold weather during early season growth also may condition onions from sets to flower.
Round onion sets produce flat onions; elongated or torpedo-shaped sets mature into round onions. Most gardeners prefer white sets for green onions, although red or yellow sets are also acceptable.
Onions from Transplants
Transplanting young onion seedlings is the method of growing that most regularly produces large, dry, attractive onions for slicing (as shown in catalog pictures). Transplants are purchased in bundles (usually 60 to 80 plants) from garden stores and through seed and nursery catalogs (though mail-order onion plants often cost as much as buying the 60 to 80 full-size mature bulbs they may produce).
Gardeners should try to match varieties to their location.
- Long-day onions are bred for best performance in the North and short-day varieties perform best in southern locations.
- Short-day varieties may perform acceptably in the North if the plants can be set out very early in the season.
- Long-day types may not get the bulbing signal in the Deep South and so should be avoided there.
The typical garden center may offer:
- Yellow and White Sweet Spanish (long-day varieties)
- Yellow and White Bermuda (short-day varieties)
- Red variety that may or may not be named (Southport Red Globe, perhaps; a long-day variety).
Catalog shoppers may choose from a slightly wider variety selection. Prices normally are two to three times as high through catalog sales and maybe as much as ten times as high. Only individual consumers can judge if this cost is justified for trying a new variety.
When to Plant
Onions can be planted as soon as the garden can be tilled in the spring, usually late March or early April in prime regions for producing onions. Good fertility, adequate soil moisture, and cool temperatures aid development.
Spacing & Depth
To produce green onions, plant the larger sets 1½ inches deep and close enough to touch one another (green onions are harvested before crowding becomes a problem). To produce dry onions, plant the smaller sets 1 inch deep, with 2 to 4 inches between sets. Allow 12 to 18 inches between rows. If sets are 2 inches apart, harvest every other plant as green onions so that bulb development of the remaining sets is not impeded by neighboring plants.
Onions from Transplants
Plant in fertile soil in early spring. Space the plants 4 to 5 inches apart in the row to produce large-sized bulbs (closer spacing significantly decreases bulb size) or space 2 to 2½ inches apart and harvest every other plant as a green onion. Allow 12 to 18 inches between rows or space onions 6 to 8 inches apart in all directions in beds. Set the transplants 1 to 1½ inches deep and apply 1 cup per plant of a starter-fertilizer solution.
Onions from Transplants
Weeds and grass compete with the onion plants for nutrients and moisture during the growing season. Remove all weeds and grass by diligent and repeated shallow cultivation and hoeing. Side-dressing with fertilizer may be necessary.
Keep onions free from weeds by shallow cultivation and hoeing. To develop long, white stems for green onions, slightly hill the row by pulling the loose soil toward the onions with a hoe when the tops are 4 inches tall. Do not hill onions that are to be used as dry onions. Hilling may cause the necks of the stored bulb to rot.
Above 40 degrees north latitude, root maggots may attack the roots of onion plants.
Pull green onions any time after the tops are 6 inches tall. Green onions become stronger in flavor with age and increasing size. They may be used for cooking when they are too strong to eat raw. Though leaves are traditionally discarded, all parts above the roots are edible.
- Remove any plants that have formed flower stalks and use them immediately. They do not produce good bulbs for dry storage.
- Harvest in late July or early August, when most of the tops have fallen over.
- Allow the plants to mature and the tops to fall over naturally.
- Breaking over the tops early interrupts growth, causing smaller bulbs that do not keep as well in storage.
Pull the mature onions in the morning and allow the bulbs to air dry in the garden until late afternoon.
- On especially hot, bright, sunny days, the bulb may sunburn.
- On days when this is likely, remove onions to a shaded location and allow them to dry thoroughly.
- Then, before evening dew falls, place them under dry shelter on elevated slats or screens or hang them in small bunches.
- Tops may be braided or tied with string before hanging.
- Full air circulation for 2 to 3 weeks is necessary for complete drying and curing.
- Keep the dry wrapper scales as intact as possible on the bulbs, as they enhance the keeping ability.
After the bulbs dry:
- Cut the tops 1½ to 2 inches long (at or above the narrow spot where the stem bent over), and place the bulb in dry storage with good air circulation.
- Do not try to store bulbs that are bruised, cut, or diseased or those with green tops or thick necks.
- Store under cool, dry conditions.
- Dry onions may keep until late winter, but check them regularly and use or discard those that begin to soften or rot.
Selection & Storage
Onions are the single most important ingredient a cook can have on hand. What versatility– choose from sweet, sharp, mild, or pungent. Because the onion family is so diverse (chives, scallions, leeks, shallots, garlic, red onions, yellow onions, and white onions), this discussion will be limited to scallions, green garden onions, and mature garden onions.
Scallions and Green Onions
Scallions can be harvested any time they look tall enough to use. Gently pull or dig well below the slender white portion when the leaves are 8 to 10 inches high. True scallions have no bulb. Select healthy bright green tops that look crisp.
Green onions or spring onions are a step above scallions although the terms are often used interchangeably. They have a 1-2 inch bulb with green tops. The smaller bulbs are sweet while the larger ones are more pungent. Left in the ground longer, the bulb will develop and become larger.
Scallions and green onions are best harvested as you use them. For longer storage, rinse soil from bulbs and dry, peeling away the first layer if necessary, trim roots, and store in the refrigerator for up to a week in perforated plastic bags.
Mature garden onions are ready for harvesting when the green top withers, falls over, and starts to turn brown. This usually happens in mid-to-late summer. Be sure to harvest before the fall rains, mature onions will rot quickly in cool, wet soil.
- Lay mature onions in a single layer on newspaper in a warm, well-ventilated place to cure for a few days.
- Leave undisturbed until the outer skin becomes papery and crispy dry.
- Select unbruised onions, rub off the stringy roots, and braid the tops.
- Hang in bunches or place in mesh bags and hang away from moisture.
- If stored in a dry cool place (50 to 60 degrees), they will keep for months
Questions & Answers
Q. I harvested my onions in late summer and they began to rot by fall. Why?
A. Onions may rot at either the base or neck. Rotting at the base may be caused by soilborne fungi or carelessness in harvesting and handling, but it is usually caused by damage from root maggots. If onion bulbs rot at the neck, either they have been cured insufficiently before storage or the leaves have been severely infected by fungi during the growing season. Onions that were "hilled" or covered with soil before harvest often start to rot soon after harvest. Many of the "sweet" varieties are very poor keepers and should be enjoyed fresh soon after harvest, as no method of storage keeps them from rotting for very long.
Q. What happens when onions are broken over?
A. They stop bulb development at that point and could be immature. As a result, they do not cure or dry properly. In some cases, the rings also separate, yielding bulbs of poor quality.
Q. My parents came from Europe, where they braided the tops of onions. Why are onions braided?
A. Onions are braided for curing and storage. After the tops are air-dried, they are braided and the onions are hung in a dry, sheltered location with good air circulation. Incorporating twine with the braiding adds strength. Individual onions may be cut from the braided "rope" as needed, leaving the rest of the braid intact.
Q. My grandparents grew winter onions. Can I grow these?
A. Yes. Hardy through most of the country, winter onions (Egyptian or walking onions) are planted from sets formed at the tops of the plant in place of flowers. Plant the sets 1 inch deep during August. Space sets 4 to 5 inches apart. The clump also may be divided in early spring (March or April) and transplanted in the same manner as other onion plants. In either case, be sure to place the winter onion bed at the side or end of your garden because these onions are perennials. Sets are available from a limited number of seed houses and can usually be obtained from other gardeners in the area.
Q. How do I grow multiplier onions?
A. Multiplier onions (sometimes referred to as "potato onions") are planted and handled in exactly the same manner as shallots. True multiplier onions, like winter onions, are difficult to obtain, though some specialty seed houses have begun to stock these old-style crops again, and can be ordered from specialty seed companies online. They are not normally grown from seeds.