Growing onions

Growing Onions and Scallions

Allium Cepa


Grown for their fleshy, aromatic bulbs and tender green stalks, Onions (Allium Cepa) are valued for their distinct, pungent flavor, their wide availability, and their versatility in the kitchen. Growing onions is simple and they have low water and maintenance requirements

Name´s Origin

The word onion comes from the Latin word Unio meaning “one,” because each onion plant produces only a single bulb.

Being a member of the Allium family, the Onion is both are rich in powerful sulfur-containing compounds that are responsible for their distinctive odor and for many of their health-promoting effects.

In addition, onions are very rich in chromium, a trace mineral that helps cells respond to insulin, plus vitamin C, and numerous flavonoids, most notably, quercitin. In many circles, the onion is considered among the healthiest of vegetables.




There are three main divisions of this vegetable: green onions (also called scallions) and the two types of “dry” onions, which are mature versions of the former. Mature Onions are either categorized as Summer (or Sweet) varieties or as Winter (or Keeper-Type) varieties. Each of the three groups comes in a wide range of shapes and colors. Pearl onions are the smallest versions with a diameter of around one-half inch, but large keeper varieties can reach a diameter of 5 inches or more. Onions come in three colors; yellow (the most common), white, or red onions.

p08B01m-2Deciding which onions to grow according to taste is a good way to select onions. Your two main options: the milder (and usually bigger) Summer types and the strong-flavored Winter varieties. A good rule of thumb: the tougher the skin and stronger the flavor of the onion, the longer it will keeps.


Green onions, scallions, are simply immature bulbs, usually picked for their tender stalks. You can pick green onions in the Spring, use first white onions for pickling and boiling, then the large, mild ones, sliced, in Summer and finally the yellow ones for cooking through Fall and Winter.


Unique Traits

Onions go through a process called “bulbing” to produce the onion bulb, which is affected by the amount of daylight, not by plant maturity. Daylight necessary to initiate bulbing depends on the variety of onion and can range from 12 hours for early maturing types to 16 hours for late maturing types.

Daylight Sensitivity:

This is why some varieties are labeled as short-day or long-day types. Long-day onions bulb only when they receive 15 to 16 hours of daylight. In general, the long-day varieties are recommended for northern areas, while the short-day varieties are intended for use in the South.


Nutrient Sensitivity:

Mature onion bulb size is highly correlated to the size of the onion plant at the time bulb formation begins. The larger and more vigorous the plants are at “bulbing” time the larger the growing onion bulbs. Factors include early planting; space per plant, soil moisture; weed competition early in the growing season, availability of nutrients, and damage from cultivation, insects and pests.


Popular varieties

Short-Day Types: Growing Onions in the South

Burgundy – A good dark red-skinned table onion with mild, sweet white flesh.

Crystal Wax – This mild-tasting small, white pickling onion has good disease resistance and has been a steady performer over the years in southern states. However, it doesn’t store well.

Granex – One of the Deep South’s most popular onions, the large, yellow bulbs may be thick-flat or almost globed. It’s an early variety, and keeps well if cured and stored properly. Granex, also known as the Vidalia onion, comes in red and white varieties.

Texas Grano 1015Y – A new strain of Yellow Grano with a sweet, mild flavor and better storing ability and disease resistance than other Texas Grano’s.

Yellow Bermuda – A flat-globed, medium-sized onion with pale straw-colored skin and white flesh. It also comes in white and red types.


Long-Day Types: Growing Onions in the North

Buffalo – An early-maturing, yellow-skinned variety that will store until late December.

Early Yellow Globe – A medium-sized bulb that matures in about 100 days and is a good keeper.

Ebenezer – Generally sold as sets, these white or yellow onions have a strong flavor and store well.

Red Wethersfield – This red onion produces flat bulbs with juicy white flesh. It’s an excellent keeper and is often sold as sets.

Sweet Sandwich – Brown skinned with light yellow flesh, this onion is an excellent keeper that gets milder with storage.

White Portugal – Excellent direct-seeded in garden for green tops and pickling-size bulbs, but not a good storage onion.

Sweet Spanish Spanish types – These onions need a long growing season, but will produce large, globe-shaped, mild-flavored bulbs. One famous type is the Walla Walla Sweet.


Onions vary in keeping qualities, too. For an onion that you can keep long after the growing season, the strong-flavored, yellow ones are your best bet. Stuttgarter, Copra, and Yellow Globe are examples of onions you can bag and hang in your root cellar in fall that will last through the winter and following spring.
different onions types


The milder Summer onions won’t keep that long. They don’t develop the really firm outer skin needed for long storage. In fact, some white sweet onions will keep for just a few weeks. They’re definitely worth growing, though, for their sweet, mild taste.



Fertile soils with adequate sunlight and drainage are ideal for growing onions. The ideal soil for growing onions is well-worked, light, and porous, with a pH of 6.6. Best are raised beds at least 4-inches high and 20-inches wide. Because they are shallow-rooted, growing onions will be directly affected by the availability of soil moisture and nutrients, especially nitrogen, phosphorus, and calcium.


The health of your crop can be directly enhanced at planting time by the addition of phosphorus-rich fertilizer, such as bone meal. Create a 6-inch deep trench below where you will be planting your onions. Sprinkle bone meal into the trench at a rate of 1 cup per 10 lineal feet and cover with a minimum of 2-inches of soil.





Onions are a cool season plant which grows well in a wide range of temperatures. Young onion plants are highly resistant to frost. High quality onions require cool temperatures during early development and warmer temperatures during maturity.


Planting seeds and transplanting sets are the two options for planting your onions. Seeding is cheapest but takes longer before onions are ready. Transplanting sets should result in earlier maturity and earlier harvest.


Planting Depth: Depth of planting onion seeds or transplanting onion sets has a dramatic impact on the shape of the mature bulb. The onion bulb forms immediately above the point where the seed germinates. Onion bulbs may form above or below the soil surface depending on the placement of the seed or set and by subsequent movement of the soil due to cultivation. It’s OK for the bulbs to stick-up above the soil, at least a little bit. But, deeper planting will result in long narrow bulbs, while shallow planting tends to produce wide flat bulbs.


Planting Onion Sets:


Seed SpacingRow SpacingPlant Spacing*Planting DepthSoil TemperatureSprout TimeLight NeedsDays to Harvest**
NA18 in.4 in.3/4 in.55°-75° F12 DaysFull-Sun100 Days


*= Plant Spacing: Spacing after Thinning OR Distance between plants (Intensive Planting)
**= Days to Harvest will vary with your climate (longer in cool climates or cool summers).

Planting Onion Seeds:

Onion seeds are tiny! For most onion varieties, about 8,000 seeds weigh an ounce, so they require careful handling. Try not to plant on a windy day. Sow seeds with the same row spacing as sets and thin to the recommended plant spacing.

Onions seeds are often planted in late fall in cooler climates to over-winter and thus get a jump start on the following year’s growing season. This method is particularly effective for varieties requiring a long growing season. Onions seeded in October-to-December or sets planted in January-or-February should produce bulbs in May-to-July.


How to fertilize onions

About three weeks after planting onions sets, or when spring-seeded onion plants are 6-inches high, begin to fertilize your growing onions with a nitrogen-rich fertilizer, such as cottonseed meal.

Sprinkle the dry material thinly on top of the soil around the plant, or scratch into the soil beside the plants.

Take care not to damage the tender, shallow roots. Continue this regimen every three weeks, until a month before harvest. When the neck (the area of stem just above the bulb) begins to soften, it is time to stop.


Watering Onions

Onions are shallow-rooted crops. Without over-watering, it is good to maintain a steady supply of damp (not wet) soil around the roots of growing onions. As your growing onions begin to form bulbs, frequent irrigation will promote good growth and helps keep the soil firm around the onion bulb. Cracks from overly dry soil create inconsistent soil pressure around the onion bulb, resulting in misshaped onions.


As growing onions begin to mature, irrigation should be stopped to allow the soil to dry before to harvest. Irrigation should be discontinued when 10 percent of the tops have begun to break over on their own, as this is an indication of bulb maturity. If moisture is not reduced as onions near maturity, softer onion bulbs may result. Softer onion bulbs may break down faster and result in greater storage problems.



Weed control

Of all vegetable crops, growing onions are the least able to compete with weeds, which can be especially damaging to young onion plants because they are slow to develop, have shallow roots and do not have enough foliage to adequately shade the ground. Hand weeding is the best control; repeated weeding will be necessary.


Any cultivation must be very shallow or it may damage the growing onion roots and cause subsequent damage to the developing plant . Tools which restrict their effect to the top 1 inch of soil are ideal.


As soon as the soil has warmed up enough to promote healthy plant growth, the application of mulch is encouraged. In addition to keeping the weeds down, mulch cools the soil which helps retain soil moisture, provides soil nutrients, and minimizes the need for cultivation.


Probable Pests

Onions do not have many insect problems. Onion Root Maggots are the most serious insect problem, especially after a series of cool, wet springs. The brownish-gray adult flies emerge in early spring and lay eggs on the onion seedling base. Upon hatching, the larvae burrow into the onion roots. Onion Maggots are most effectively controlled by applying a fertilizer in the furrow when planting.


Thrips are very small (one-sixteenth inch) cream- to brown-colored insects which migrate into fields in the summer are found between the center leaves. Multiplying rapidly during hot, dry weather, thrips cause a rasping type of feeding injury to onion leaves, but can be controlled with a strong jet of water. A small amount of leave damage is acceptable, as if will not significantly affect the bulb development.


Potential Disease

Growing Onions are generally resistant to major diseases. The best protection is prevention; by maintaining healthy plants and by choosing varieties appropriate for your locale. Of the diseases that do affect growing onions, nearly all are fungal diseases, often brought about by excess humidity or by wet and poorly draining soils.


Smut is a common infection of growing onion seedlings that is most effectively controlled through crop rotation and using a fungicidal seed treatment. Fungicide mixed with onion seed may be used to prevent smut infections. Pink Root is also caused by common soil fungi and can be best prevented through crop rotation.


Downy Mildew and Purple Blotch are diseases that may be a problem during periods of very high humidity.


Leaf Blight and Neck Rot caused by fungus, Botrytis Squamosa. Botrytis-resistant varieties are the best defense from this disease. Basal Root Rot may cause serious crop losses but can be controlled by planting Fusarium-resistant varieties.



Onions may be picked as green onions from the time they are pencil size until they begin to form bulbs. If you are growing onions for their bulbs, let the plants grow larger.

Onions are ready when the main stem begins to get weak and fall. Check the neck to see if it feels soft. Flowers will also appear when onions reach this stage in their development


When the plant has fallen over, pull the plants out of the soil. If its not going to rain, let them lay in the garden for a day or two to dry. Then remove the tops and roots and let them keep drying in baskets or boxes.


How to storage your onions

Onions prefer to be stored in a Class C (Cool Dry) storage area, with a temperature range of 32 to 55 degrees F, and relatively humidity of 50% to 60%. For short-term storage, they will keep well for up to three weeks in your kitchen.

It is best to store them in a lower cabinet, open to the air, out of the light, and away from moisture. Once cut, store an onion in the refrigerator for up to a week.

Because their pungent odors can carry into other foods, place cut onions inside a sealable plastic bag and place that bag within another sealable plastic bag.




Onions are one of the most essential ingredients in cuisine across the World. They can be used in their immature form, as scallions, or in their ripe state, as the well-known onion bulb.

Praised for their distinctive and strong flavor, onions can be baked, boiled, braised, fried, grilled, used raw, roasted, sauteed, or steamed.


Their flavor matches well with: apples, bacon, butter, cheese, cinnamon, cloves, cream, mushrooms, nutmeg, paprika, Parmesan cheese, parsley, pepper, raisins, sherry, thyme, tomatoes, vinegar, Worcestershire sauce, beef, rice, and more. Visit our Kitchen for some of our favorite Recipes. Share some of you own!


Crop Rotation

Growing onions in a four-year crop rotation plan: group Onions and other Alliums (Garlic, Shallots, Leeks), with the Legumes family of plants, such as Peas and Beans.

While listed as incompatible with Peas and Beans in traditional lists of Companion Plants, in our test gardens, growing Onions adjacent to Legumes do not seem affect either group.

And, because of their need for nitrogen throughout their growing season, growing onions appear to benefit from the nitrogen-fixing processes of the legumes. We recommend that you separate any Allium plant from any Legume plant by one foot.


 Companion plants

  • Shallots
  • Beets
  • Garlic and Elephant Garlic
  • Cabbage
  • Leeks
  • Carrots
  • Lettuce