Onion is a bulbous perennial or
biennial herb believed to be native to western Asia. Numerous varieties are
cultivated worldwide. Onion bulb has been used as a food for thousands of
years. It has also been used medicinally. Its actions were considered to
be comparable to those of garlic, though milder.
Onion is used for loss of appetite and
prevention of atherosclerosis and age related change in blood
vessels. May reduce the risk of gastric cancer. The Commission
E reported antibacterial, lipid, and blood pressure-lowering properties and
inhibition of thrombocyte aggregation. Recent investigations suggest that
therapies aimed toward the prevention of atherosclerosis should include a diet
rich with onions. Contemporary studies have shown that onions, like garlic, may
inhibit platelet aggregation and interfere with fibrinolyis. Clinical
studies have reported that onions lowered lipid levels and inhibited the
formation of blood clots. Onions are also cooked in milk and eaten in
order to clear congestion in the lungs.
Onion bulb contains numerous organic
sulfur compounds, including trans-S-(1-propenyl) cysteine sulfoxide,
S-methyl-cysteine sulfoxide, S-propylcysteine sulfoxide, and cycloalliin;
flavonoids; phenolic acids; sterols including cholesterol, stigmasterol,
b-sitosterol; saponins; sugars; and a trace of volatile oil composed mainly of
sulfur compounds, including dipropyl disulfide. A fresh onion bulb
contains fructans with a low degree of polymerization, flavonoids, and
sulfur-containing compounds. When an onion bulb is bruised, the sulfoxides are
degraded by alliinase and release pyruvic acid and alkylthiosulfinates, which
rapidly form into disulfides.
Unless otherwise prescribed: 50 g per
day of fresh bulb or 20 g per day of cut dried bulb, pressed juice from fresh
onions and other oral galenical preparations. Dried bulb: 20 g.
Fresh bulb: 50 g. Infusion: Steep 12 teaspoons in 120 ml
water. Tincture: 5 ml (1 teaspoon), three to four times
daily. If onion preparations are used over several months, the
daily maximum amount for diphenylamine is 0.035 g. HYG-1616-92 Marianne Riofrio E. C. Wittmeyer
is one of the most important vegetables grown and is very popular in home
gardens. Onions commonly grown are the mild types, such as White and Yellow
Sweet Spanish or the more pungent globe types. The pungent onions are better
suited to long-term storage.
The common onion (Allium cepa), the most
popular and widely grown in home gardens, is grown from either seed, plants or
sets for use as both green onions and dry bulbs. The home gardener will usually
have more success with sets. Any standard onion variety or hybrid can be used
for green bunching onions if harvested at the proper stage of maturity.
Onions can be used as green onions within 30 days if grown from plants
or sets; or 40 to 50 days if grown from seed. There are, however, bunching
varieties that produce a true bunching onion or scallion with either small or
no bulbs. For dry onions from sets or plants, 100 or more days are required
from planting, depending on the variety grown.
The potato or multiplier
onion, and the Egyptian onion are grown from vegetative parts rather than seed.
In the case of the multiplier or potato onion, the underground portion is a
compound bulb formed from the segregation of a large mother bulb. Each bulb in
the compound bulb produces 6 to 12 plants. Their principal use is the
production of early green bunching onions.
The Egyptian onion produces
clusters of small bulbs called bulbils at the top of the seed stalk in late
summer. The bulbils are used to produce very early green onions. Both
multiplier and Egyptian onions are planted in the fall, overwintered with some
mulch protection, and brought into production in the early spring. Due to this
method of culture, the onions are referred to as "winter onions".
The onion is adapted to a
wide range of temperatures and is frost-tolerant. Best production is obtained
when cool temperatures (55 F to 75 degrees F) prevail over an extended period
of time, permitting considerable foliage and root development before bulbing
starts. After bulbing begins, high temperature and low relative humidity
extending into the harvest and curing period are desirable.
supply of adequate moisture is necessary for best results. For onions started
from plants, a light mulch will help conserve moisture for uniform growth. An
important aspect of onion development is the length of day or photoperiod.
Photoperiod, along with temperature, controls when the onions form bulbs. Some
onion varieties are short-day in response, and form bulbs when the days are 12
hours or less in length.
Other varieties are long-day plants, forming
bulbs when there are 15 or more hours of daylight. This effect of day length
makes some onion varieties unsuitable for northern climates because they begin
to bulb when the plants are too small. The influence of day length also
requires that Sweet Spanish and Bermuda onions be grown from plants rather than
Unfavorable growing conditions may result in onions bolting or
sending up flower stalks. If flower stalks should develop, carefully cut them
from the plant immediately or bulbing will be reduced. Soil Requirements Onions
grow best in a loose, well-drained soil of high fertility and plenty of organic
Avoid heavier soils such as clay and silt loams unless modified
with organic matter to improve aeration and drainage. Onions are sensitive to
highly acid soils and grow best when the pH is between 6.2 and 6.8. Fertilizers
As for most vegetables, lime and fertilizers are best applied using the results
of a soil test as a guide.
Fertilizers of a 1-2-2 ratio (5-10-10, for
example) are good for onion production. As the onion plant's root system is
very limited, high soil fertility is essential for good production.
Establishing the Planting
Onions should be
planted early in the spring as soon as the soil can be worked. Onion seed is
sown 1/2 inch deep, while sets are planted one to two inches deep. A three-inch
plant spacing is desirable. Rows should be 12 to 18 inches or more apart
depending on the method of cultivation. For wide row planting, plants or sets
are placed on 3-inch centers. Onions are ideal for wide row planting, but keep
in mind that weeding must then be done by hand.
Green (bunching) - White Portugal, Tokyo Long White,
Beltsville Bunching, White Spear, Ebenezer, Yellow Globe strains. Dry (storage)
- Ebenezer, Yellow Globe strains, Elite, Stuttgarter (from sets). Sweet (from
plants) - White or Yellow Sweet Spanish, Bermuda.
After the plants are well-established, a mulch will
conserve soil moisture, prevent soil compaction and help suppress weed growth.
In windy areas, small plants must be protected with a windbreak of some type to
prevent serious damage or loss of plants.
Weeds, insects, and diseases
must be controlled. Thrips, onion maggots, downy mildew, neck rot, pink root,
and smut are problems that can occur in onion planting.
Harvesting, Curing and Storing
Harvest onions when the
tops have fallen over and dried. On sunny, breezy days, onions may be pulled
and left in the garden for a day or two to dry before they are taken to a
curing area. Curing must take place for the onions to be stored for any length
Cure onions by placing them in a warm, well-ventilated area
until the necks are thoroughly dry. With warm temperatures, good air
circulation and low humidity, curing should be completed within two weeks after
harvest. Onions are best stored in a cool moderately dry area in ventilated
The authors gratefully acknowledge J.D.
Utzinger and W.M. Brooks for authoring the 1984 fact sheet on which this is
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