An onion is a vegetable plant that is widely cultivated that has many layers in each other. The scientific name of onion is Allium Cepa, which belongs to the family of amaryllis. Onions have green leaves that grow from the bulbs found underground.
Onions are commonly used for cooking for its flavor and aroma. It can also be eaten raw . Onions vary in size, color and shape. There many varieties of onions. These varieties are different in flavor, texture and use.
Types Of Onions
1. Red onion. They are mostly eaten raw in sandwiches, and salads due to their sweetness and color that is reddish-purple
2. Yellow onions. They are mostly used for cooking due to their flavor that is not too sweet nor sharp.
3. White onion. These onions have sharp flavor as compared to yellow onions
4. Shallots. This variety have mild flavor. They grow like garlic cloves. They are mostly used for dressing, sauces
5. Green onion. This type of onion is mostly used for garnishes in many dishes. The are pre-mature onions that has not produced bulbs.
6. Sweet onion. They are either used for cooking or eaten raw. They have low sulfur which makes them sweeter than other varieties.
7. Leeks. It has subtle flavor that is more earthier than other onion types. It's mostly used for stocks .
8. Cipollini onion. They can be yellow or red. It's flat in shape and have thin skins.
9. Torpedo onion. They are long in shape and are reddish in color. They are suitable for roasting and grilling because of the mild sweetness.
10. Pearl onion. They are small in size and are sweet.
How To Grow Onions From Seed 
To grow Onions we start by choosing the right onion varieties. Choose the variety according to the climate you have and what you want to do with the onions.
Onions do well in temperate climates without extreme heat or cold. It should be noted that they are two main types of onions that is, long-day onions and short-day onions . Long-day onions do well in the northern states while short-day onions do well in southern states.
When you most have chosen the varieties you want to grow, prepare the pots that you will germinate your onions in.
It's necessary to start onions seeds indoors especially in colder areas.Sow the seeds in to the pots, space them 2cm apart and lightly cover the seeds with compost soil. Place the pots in warm water to be moisten. When the seeds are moisten, place the pots in a warm location until it germinates.
Keep the seeds indoors for 10- 14 weeks. When the seedlings had sprouts, keep the lights on for about 18 hours a day and off for 6 hours to keep the seedlings healthy so as to grow well. Water regularly and fertilize them in order to keep the soil moist.
When the seedlings has grown a bit taller, transplant them into the garden. The onion seedlings need 4-6 weeks of warm temperatures to establish in the ground. When planting, add nitrogen fertilizer and organic fertilizer in to the bottom of each row before planting.
Plant the seedlings in the same depth that they were found in their pots. Space them 5-6 inches apart.
How To Care For Onions
1. Watering. Use a watering can to water the plants regularly to keep the soil moist. This will help settle soil around the roots. Stop watering when the leaves are yellow. When the leaves are yellow it means the bulbs are swell.
2. Fertilizing. Onions are heavily feeders. Chemical fertilizers aren't really needed in growing onions. Tilling the soil and putting compost are always enough for the onions. If the soil is really poor in fertility, add organic because they are not harmful to the plant nor the soil.
3. Weeding. Weed the garden to remove unnecessary weed because onions do not grow well when its compete with weed over the nutrients and water found in the ground. Mulching can help suppress weeds.
4. Remove flowers. Remove flowers that come from onions plants as early as possible because if the flowers are not removed early, the plant will concentrate in producing flowers instead of producing big bulbs.
Pests And Diseases Affecting Onions
Diseases
1. Black mold. It's caused by fungus. The symptoms of black mold are seen on the bulbs. The whole body of the bulbs becomes black and shriveling.
To control black mold, treat seeds with fungicide before planting to reduce rot in mature onions. When harvesting, be careful to avoid bruising the onions bulbs and keep the bulbs under temperature at 15c
2. Downy mildew. Downy mildew are caused by fungus. It manifest itself on the leaves as the leaves become pale, yellow, gray-purple fuzzy grow on leaves. This disease occurs when the temperature is cold . To combat this disease, crop rotation should be done.
This will help minimize disease problems. Plant onions in well drained areas and avoid planting infested onions.
3. Leaf streak and bulbs rot. This disease is caused by bacterium. It cause dark green oval lesions on leaves, dark spots on bulbs, the inner part of bulbs become reddish-brown. To overcome this disease, spray the plant with bacteriacideal and avoid fertilizing during winter.
Pests
There are several pests that attack onions such as; onion maggots, leaf miners,thrips and bulbs mites. These pests are either caused by arachnids (bulbs mites) or by insects (leaf miners, onions maggots and thrips).
-bulb mites makes bulbs rotten in the ground or when they are store. To control this, there should be crop rotation .
-leafs miners cause leaves to fall off and it reduces crop yields
-onion maggot deformed the bulbs , make seedlings to be stunted
-thrips makes the leaves to change its color from green to silver. To control these pests attacking onions, one and the same crops should not be planted on the same garden over and over,use insecticide to spray the plants, the plants should be thoroughly inspect before planting and immediately after harvest, the plants should be removed.
Harvesting 
Onions takes 3-4 months to be mature from seeds. The foliage or leaves of onions are great indicator for its maturity.
When the leaves become yellow or brown and start falling off, it's a sign that they are ready for harvest. Onions can be harvested by gently pulling them by their foliage or by using garden fork . The forks are inserted in the ground under the bulbs and then lift them up.
Try to keep the full stem intact to avoid any possibility of rot. If the climate is dry, the bulbs can be kept on the farm for 2 or 3 days before curing. But if the climate is wet then move the bulbs immediately to a dry location.
Saving Onion Seeds
Though this isn’t a post on how to save onion seeds, it’s important to note that onions are biennial crops, meaning they go to seed in their second year.
If you happen to have onions that blossom in the first year, you don’t want to save those seeds (you can chop the blossom off and use it as you would green onions though!), and you don’t want to plant those seeds because you’re perpetuating a crop that’s bolting too soon.
Furthermore, those onions that flower in their first year won’t be good storage onions, even if they’re a good storage variety, so go ahead and pull them out of the garden and use them right away.
If you want to save onion seeds, you actually have to leave the onion in the ground until the next season and harvest the seeds from the flowers that blossom in that second year. One onion will give you quite a few seeds, so it’s not necessary to leave too many onions in the ground.
How To Store Onions .jpg "how to grow onions from seed")
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An ideal condition to store onions are warm areas, dark, dry breezy, and out of the sun. Make sure your onions have enough space for circulation of air to avoid rotting and maintain flavor. Turn the onions after few days for it to dry thoroughly. Store the onions in a mesh bag, orchard rack,bushel basket.
Conclusion
To achieve a successful harvest in onions, you must be able to choose the right varieties of onions that suit the climate you have, prepare the seeds and soil well for planting and takes good care of the plants by watering regularly, weeding , removing flowers and fertilizing them when needed for the onions plants to yield big bulbs.