Onion. Allium cepa, Amaryllids Family ( Amaryllidaceae ), Commonly Known As: Onion. We wish to thank Wikipedia, the free encyclopedia for some of the information, and images on our page. We share information, images, and donate to Wikipedia. The onion (Allium cepa L.) (Latin cepa = onion), also known as the bulb onion or common onion, is a vegetable and is the most widely cultivated species of the genus Allium. The onion plant has a fan of hollow, bluish-green leaves and the bulb at the base of the plant begins to swell when a certain day-length is reached. In the 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. The crop is prone to attack by a number of pests and diseases, particularly the onion fly, the onion eelworm, and various fungi cause rotting. Some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs. An onion plant is composed of leaves which arise alternately from a small �attened stem, or base plate, so that older leaves are on the outside and younger leaves on the inside of the stem. Each leaf is composed of a photosynthetic leaf blade and a non-photosynthetic, storage leaf base (scale). During the growth of the plant the leaf scales thicken and form the characteristic bulb. Onions have a determinate growth habit. At the onset of bulbing, leaf sheaths swell, bladeless bulb scales are initiated and these swell to form the central storage tissue of the bulb. Leaf blades initiated prior to bulbing develop to full expansion and the green top lodges at `top down'. Mature onion bulbs can range in size from 5 mm to over 100 mm bulb diameter. Onions are cultivated and used around the world. As a food item, they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which irritate the eyes. The onion plant is unknown in the wild, but has been grown and selectively bred in cultivation for at least 7,000 years. It is a biennial plant, but is usually grown as an annual. Modern varieties typically grow to a height of 15 to 45 cm (6 to 18 in). The leaves are yellowish-green and grow alternately in a flattened, fan-shaped swathe. They are fleshy, hollow, and cylindrical, with one flattened side. They are at their broadest about a quarter of the way up beyond which they taper towards a blunt tip. The base of each leaf is a flattened, usually white sheath that grows out of a basal disc. From the underside of the disc, a bundle of fibrous roots extends for a short way into the soil. As the onion matures, food reserves begin to accumulate in the leaf bases and the bulb of the onion swells. In the autumn, the leaves die back and the outer scales of the bulb become dry and brittle, and this is when the crop is normally harvested. If left in the soil over winter, the growing point in the middle of the bulb begins to develop in the spring. New leaves appear and a long, stout, hollow stem expands, topped by a bract protecting a developing inflorescence. The inflorescence takes the form of a globular umbel of white flowers with parts in sixes. The seeds are glossy black and triangular in cross section Onions are best cultivated in fertile soils that are well-drained. Sandy loams are good as they are low in sulphur, while clayey soils usually have a high sulphur content and produce pungent bulbs. Onions require a high level of nutrients in the soil. Phosphorus is often present in sufficient quantities, but may be applied before planting because of its low level of availability in cold soils. Nitrogen and potash can be applied at intervals during the growing season, the last application of nitrogen being at least four weeks before harvesting. Bulbing onions are day-length sensitive; their bulbs begin growing only after the number of daylight hours has surpassed some minimal quantity. Most traditional European onions are referred to as "long-day" onions, producing bulbs only after 14 hours or more of daylight occurs. Southern European and North African varieties are often known as "intermediate-day" types, requiring only 12�13 hours of daylight to stimulate bulb formation. Finally, "short-day" onions, which have been developed in more recent times, are planted in mild-winter areas in the fall and form bulbs in the early spring, and require only 11�12 hours of daylight to stimulate bulb formation. Onions are a cool-weather crop and can be grown in USDA zones 3 to 9. Hot temperatures or other stressful conditions cause them to "bolt", meaning that a flower stem begins to grow. Onion varieties also have different requirements as to the number of hours of daylight required to make a bulb. If the seed catalog lists the onion as long day, it sets bulbs when it receives 15-16 hours of daylight and is used to produce onions in Northern summers. Short day varieties set bulbs with about 12 hours of daylight and are used in the deep South for winter production. Onions may be grown from seed or from sets. Onion seeds are short-lived and fresh seeds germinate better. The seeds are sown thinly in shallow drills, thinning the plants in stages. In suitable climates, certain cultivars can be sown in late summer and autumn to overwinter in the ground and produce early crops the following year Onion sets are produced by sowing seed thickly in early summer in poor soil and the small bulbs produced are harvested in the autumn. These bulbs are planted the following spring and grow into mature bulbs later in the year. Certain cultivars are used for this purpose and these may not have such good storage characteristics as those grown directly from seed. Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow-rooted and do not need a great deal of water when established. Bulbing usually takes place after 12 to 18 weeks. The bulbs can be gathered when needed to eat fresh, but if they will be kept in storage, they should be harvested after the leaves have died back naturally. In dry weather, they can be left on the surface of the soil for a few days to dry out properly, then they can be placed in nets, roped into strings, or laid in layers in shallow boxes. They should be stored in a well-ventilated, cool place such as a shed. Here Are Some Of The More Popular Types Of Onion Plants: The Walla Walla Sweet Onion: Introduced by Walla Walla, Washington in the late 1800�s. An early producer of large and sweet, squat yellow bulbs. A favorite for county fairs and farmers' markets. Walla Walla onions have half the sulfur of an ordinary yellow onion. Matures in 90 days. Open-pollinated. Long-day onion. The Texas Super Sweet Onion: Considered to be one of the most flavorful onions on the planet. Can keep more than two months after harvest. Vigorous plant with high yields and good disease resistance. Developed by Texas A&M.; Matures in 115 days. Open-pollinated. Short-day onion. The Ringmaster Onion: The best white onion in the long-day category. Large, crisp rings make it a favorite of onion ring lovers. Sweet and mild flavor. Matures in 105 days. Resistant to pink root disease. Open-pollinated. Long-day onion. The Red Zeppelin Onion: Large, uniformly round bulbs are dark red color, high in onion flavor. Matures in 110 days. Hybrid. Long-day onion. The Lancelot Leeks: Taste is unique, although often compared to a mild onion. Attractive, blue-green tops complete tender white sheaths. Reaches 12-14 inches in length. The Dutch Yellow Moon Shallots: The gourmet onion. Golden-skinned, white-fleshed relative of the onion. Taste is like onion with a hint of garlic; bold with hints of sweet. Prolific yields. Use fresh in salads, in saut�es, or whenever green onions are called for. Each bulb yields 3-4 shallots. Pull bolting plants and use as scallions. Harvest in summer after leaves wither. Stores well.. The Dutch Red Picasso Shallots: Gourmet flavor and easy to grow! Red-skinned, pink-fleshed member of the allium family. Taste is similar to garlic and onion but more mild and rich. Use fresh in salads, in saut�es, and roasted. Each bulb yields 3-4 shallots. Not prone to bolting. Harvest in summer after leaves wither. Stores well. The Copra Onion: A favorite for storing. Keeps well for about 10 months, providing onions for cooking until planting time rolls around again. Exceptionally sweet with a bold onion flavor. Round, medium-sized onions have a dark yellow skin and thin necks. Matures in 110 days. Hybrid. Long-day onion.. The Candy Hybrid Onion. Sweet and mild flavor. Transplants well almost everywhere across the country, developing strong root systems. Matures early, producing a colossal bulb size. This small-necked beauty has a globe shape and attractive golden-brown color. Matures in 90 days. Disease-resistant. Hybrid. Intermediate-day onion.. Planting Onions In Arizona: Decide on the site for your onion plants some months in advance of planting. 1. Determine the last expected spring frost date for your area. Plan to plant your onion plants after that date. Several days below 50�F or one or two days below 30�F will cause sets to bolt, so do not plant too early. Onion varieties also have different requirements as to the number of hours of daylight required to make a bulb. If the seed catalog lists the onion as long day, it sets bulbs when it receives 15-16 hours of daylight and is used to produce onions in Northern summers. Short day varieties set bulbs with about 12 hours of daylight and are used in the deep South for winter production. 2. Cultivate your planting area to break up any hard soil, keeping your rows about 2 feet apart. Onion varieties prefer well-draining, sandy, loose soils with plenty of organic matter. Try to avoid clay soils, they produce pungent onion bulbs. 3.Onions are heavy feeders. If a soil test has not been taken, make a preplant application of 4 to 5 pounds 10-10-10 per 100 square feet before planting. Use starter solution for transplants. Sidedress 1 to 2 weeks after bulb enlargement begins using 3 tablespoons 33-0-0 per 10' row. AGAIN NOTE; Clay soils usually have a high sulphur content and produce pungent bulbs. ALSO, Avoid using fertilizers high in sulfur. 4. Purchase certified onion plants from your local garden center or nursery. 5. Onions should be spaced 1 to 6 inches by 12 to 24 inches for standard spacing; 4 inches by 4 inches for wide rows. Rows should be 2 feet apart. 6. Water your onions once or twice a week when the soil feels dry to the touch. Do Not Spray Water On Your Plants. Onions have shallow root systems so they only need a light watering to maintain constant soil moisture. Water sufficiently to moisten the soil to a depth of at least 6 inches. Mulching can help to provide uniform moisture, conserve water and reduce weeds. 7. Monitor your onion plants for disease and pest problems. Onions grown in by spraying water in Arizona, often suffer from late blight, which can be treated with a fungicide. Control common pests such as snails, potato tubermoth and aphids by sprinkling nontoxic diatomaceous earth around the affected onion plants. 8. Onions should be ready for harvest in about 100 to 120 days for mature bulbs. days after transplanting. When starting from seed, expect 100 to 120 days to maturity. Harvest onions when they reach full size. Onions should be harvested when about two-thirds of the tops have fallen over. Careful handling to avoid bruising helps control storage rots. Onions may be pulled and left in the field for several days to dry then cured in a well ventilated attic or porch for one to two weeks out of direct sun. Tops may be left on or cut off; but leave at least one inch of the top when storing. Thorough curing will increase storage life. Reduce disease problems by: �Rotating planting locations. �Removing all plant debris from the garden each year. �Purchasing disease-free onions. Inspect plants and be sure they have no spots or lesions on them at the time of purchase. Pests Of Onion In Arizona: Diseases: Neck or stem rot, bulb rot. Insects: Thrips, onion root maggots. Cultural: Bulb rot from bruising, insufficient drying; split or double bulb from dry soil during bulb formation; very small bulb from too late planting or too dry soil. To control thrips�tiny insects about as fat as a sewing needle�take a dark piece of paper into the garden and knock the onion tops against it; if thrips are present, you will spot their tan-colored bodies on the paper. A couple of treatments with insecticidal soap kills them. Follow the package directions. Spray the plants twice, three days apart, and the thrips should disappear. Onion Maggots: Cover your emerging onion crop with a fine mesh netting. Seal it by mounding soil around the edges. The onion maggot likes to lay its eggs at the base of plants, so the netting should prevent that. You should also keep mulch away because the insects like decaying organic matter, and make sure you completely harvest your onions as the season progresses. Onion maggots are usually a problem in very rainy periods, so these precautions may be unnecessary if you have a dry season. Here is a link to our page of fruit tree pests in Arizona; where you read descriptions and see pictures of the common fruit tree pests of Arizona. You also can learn about how to kill or control the Pests. Common Fruit Tree Pests Of Arizona. Beneficial Insects Of Onions In Arizona: Not all insects found in our gardens, & orchards are pests. Many organisms benefit the grower by eating or parasitizing pests in the orchard. These organisms are known as beneficials, natural enemies, or biological control agents. They may be native or introduced from other areas. Beneficial natural enemies (insects and mites) that may occur in our gardens, & orchards could be classified as predators or parasitoids. Predators are those that attack, kill, and feed directly on a pest (prey). Examples of common garden, or orchard predators are ladybeetles, flies, lacewings, wasps, bugs, ants, spiders, and predator mites. Parasitoids are insects that lay eggs on or in a pest (host). The developing larva lives and feeds on the host, parasitizing and eventually killing it. Examples include parasitic wasps such as the egg parasite, Trichogramma sp. Bees are a different class of beneficial insects in the garden or orchard in that they benefit the grower by aiding pollination. It is important that growers are able to recognize, identify, and conserve beneficials in their gardens, & orchards. Conservation of beneficial organisms is a basic tenet of an ecologically sound pest management strategy. Conservation or enhancement of beneficials can be achieved through judicious use of pesticides such as spraying only when and where needed, accurate timing of sprays, and selecting pesticides that are least toxic to beneficials. For Example: Many growers now place colonies of the Blue Orchard Mason bees in their orchards to pollinate their crops for maximum production. Quick Notes: Type: The part that is eaten is usually the bulb, but sometimes the leaves are eaten. Bulbs are defined as underground-modified leaf shoots with modified scales or buds. Height: About 1 - 2 feet. Spread: About 1 - 2 feet wide. Flowers: A Cyme, which is a flat-topped inflorescence in which the central flowers open first, followed by the peripheral flowers. The Iinflorescence is White, Yellow, Pink, or occasionally Purple. Flower petal length 3�4.5 mm Petal fusionthe perianth parts are separate. The position of the ovary is above the point of the petal and/or sepal attachment. Seeds: Glossy black, & triangular in cross section. Small Seeds (2.10 to 2.36 mm) or Large Seeds (2.37 to 2.76mm). Fruit: The fruit is a capsule (splits along two or more seams, apical teeth or pores when dry, to release two or more seeds). Fruit Length Up to 5 mm. Blooming Time: Spring. Flower initiation starts only after a juvenile phase, when the plant has a minimum number of 4 - 14 leaves, including leaf initials. Leaves: The green leaves are growing only at the base of the plant (basal). The leaf blade is linear (very narrow with more or less parallel sides); they have a hollow center. Leaf blade length is 100�500 mm. Elevation: 0 - 9,600 feet. Hardiness: USDA Zone 3a: to -39.9 �C (-40 �F) USDA Zone 3b: to -37.2 �C (-35 �F) USDA Zone 4a: to -34.4 �C (-30 �F) USDA Zone 4b: to -31.6 �C (-25 �F) USDA Zone 5a: to -28.8 �C (-20 �F) USDA Zone 5b: to -26.1 �C (-15 �F) USDA Zone 6a: to -23.3 �C (-10 �F) USDA Zone 6b: to -20.5 �C (-5 �F) USDA Zone 7a: to -17.7 �C (0 �F) USDA Zone 7b: to -14.9 �C (5 �F) USDA Zone 8a: to -12.2 �C (10 �F) USDA Zone 8b: to -9.4 �C (15 �F) USDA Zone 9a: to -6.6 �C (20 �F) USDA Zone 9b: to -3.8 �C (25 �F) Soil pH requirements: 5.6 to 6.0 (acidic) 6.1 to 6.5 (mildly acidic) 6.6 to 7.5 (neutral) 7.6 to 7.8 (mildly alkaline) Light: Full Sun. Habitat: Mulched areas. Well-drained soil with a 5.8 and 6.5 pH. According to Clemson University. Native: Native to Western Asia. Miscellaneous: In Yarnell, Arizona. Hardy Temp: 32�F. Water regularly; do not overwater.

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