How Many Varieties Of Onions Are There?

By Paul Smart •  Updated: 09/19/20 •  7 min read

How Many Varieties Of Onions Are There? Within the Allium family, which Onions belong to, there are approximately 600 to 900 species that exist. However, these species include plants that are closely related to Onions, such as Leeks and Chives. The Onion varieties can be classified as bulb forming and non bulb forming varieties.  Within the bulb forming Onions, they can be further classified into groups, based upon their physiological characteristics. 

What Are The Different Types Of Bulb Onions?

When classifying bulb Onions by physiological characteristics, there are three main groups; short, intermediate and long day Onions.  The physiologic difference is that the leaf blade cells, which produce the green tops of the Onion in this type, are inhibited as the day length increases.  This allows the production of bulb scales to increase, which results in the formation of the bulb. 

The extent to which this occurs, varies between different varieties, resulting in the bulb formation being dependent on day length. These physiological characteristics affect the latitude at which the Onions can be grown, and the timing of the harvest, in regions where multiple varieties can be grown.  The further the region is away from the equator, the greater the range of Onions that can be grown.  

Short Day Onions

Short Day Onions Require Around 10-12 Hours Of Daylight to create a bulb.  These varieties are the only type that can be grown in regions with 35 Degrees Latitude, North or South of the equator. These Onions generally have a sweeter taste, and are higher in sugar and water content.  It makes them suitable for immediate use, but they generally don’t store as well.  In colder regions, these short varieties may be used to produce an earlier harvest of Onions.


These Varieties Require A Day Length Of Around 13 to 14 hours per day, to create a bulb. They are most suited to regions that are between 35 to 45 degrees, from the equator.

Long Day Onions

Long Day refers to Onions that can only be grown at Latitudes of 45 Degrees or more.  These varieties require 15 hours or more of daylight, to create a bulb.

How To Grow Onions

Onions thrive in a variety of temperature ranges, but they produce the best at 12 to 23°C (55 to 75°F), and most varieties are hardy to -6°C (20°F), at least.  Onions are generally planted, in moderate to cool climates, in late Winter to early Spring, depending on what your climate will allow.  One of the lowest cost of sources of seeds in the US is Seed Now, if you live in the UK I would recommend Thompson & Morgan. Both companies have very broad product offering and include a range of early and late varieties of Onions available as well as onion sets.

Onions can be sown directly into the ground, however it is recommended that you start Onions in modular trays, because it allows them to be sown in clumps (or multi-sown).  When multi-sowing Onion seeds, ideally aim for 4 to 5 seeds per module, this will allow the Onions to reach a reasonable size.  Any more than 4 to 5 Onions in a clump, will result in small bulbs being produced.

There are several advantages associated with multi-sowing.  It allows a larger number of seeds to be sown in a tray, when transplanting the seedlings in clumps, it is much faster than transplanting individual seedlings and it makes controlling weeds easier.  This is because the clumps may be spaced a reasonable distance apart, allowing a Dutch Hoe to be used to remove weeds, which is generally much faster than hand weeding.       

It should be noted, that it is possible to plant up to 10 seeds per tray, and pick an initial harvest of Spring Onions to thin the clumps.  Onions can be harvested at virtually any point, depending on the size of the Onion desired. 

If planting in trays, Onion seedlings can be planted out after 4-6 weeks, however, it is possible to leave them in the trays for a much longer period of time, if space is not yet available in the garden.  When transplanting clumps into the garden, a spacing of 30 cm (12 inches) is recommended. 

Onions will grow in a wide variety of soils, from heavy clay to sandy soil. However, the addition of organic compost or manure, is often beneficial as it helps to retain moisture and feed the plant. Onions prefer a slightly acidic soil, like most vegetables, with a pH range of 5.5-6.5, being absolutely ideal. To find out more about how to test the pH of soil and adjust it, go to

During the growing season, they require very little maintenance apart from thinning the clumps if multi-sowing, and keeping the weeds clear. Onions can be harvested and eaten at any stage, throughout the season, however when Onions reach their full maturity, their stems will turn brown and collapse.  This signals that the Onion bulbs will not swell any further and have reached their maximum size.

Harvesting And Storing Onions

Once the Onions are ready to harvest, they can be picked, with the dried stems still attached, ready for curing.  The curing process, ensures that the outer most layers of the Onion become dry, which reduces the chances of rotting, thus maximising the storage life. To achieve this, the Onions should be spread out in a dry spot inside to a greenhouse, patio, garage or shed.  

A space saving way to do this, is to use bread crates, as they are stackable and will allow many layers to be put on top of one another. These crates are also a suitable option for long term storage as well, after the curing process is complete.  Once they have dried out, brush off any remaining dirt but do not wash them, and remove any loose layers of skin.  

Whole Onions should be stored in crates or containers, that allow a reasonable amount of ventilation in a cool, dry and dark location. An option to maximise ventilation, is to braid the Onions onto a string. 

The traditional method of “braiding” Onions, starts with a single Onion with its stem securely tied onto the end of a string.  The other end of the string should be tied to the point you wish to hang the Onions, throughout the store period. 

For the next layer, select two Onions of similar size, and wind the stems together so that they are securely attached to each other, by the stems with about 5cm (2 inches) between the bulbs.  Wind the section of stem between the two Onions, around the string once or twice before and pushing it downwards until the Onion comes into contact with the first Onion.  Repeat this process until the braid has reached the desired height.

As these instructions may be a little cryptic, it may be worth watching Harry Dodson, the Head Gardener of Chilton Estates, in the UK for almost 50 years, demonstrating the technique. Harry Dodson shot to fame in the late Eighties when he starred in the BBC series Victorian Kitchen Garden.  The series followed Harry for a full year, as he revived many of the long lost garden techniques of the Victorian Era.  This series is one of my absolute favourites, as Harry uses an amazing array of growing and storing techniques.  I would highly recommend this to anyone interested in broadening their garden knowledge.

The video below is a full episode of Wartime Kitchen and Garden, go to 8 minutes and 16 seconds, to find the section on Onions with Harry.


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Is An Onion A Root Or Stem? What Part Of The Plant Are We Eating?

Is An Onion A Vegetable?

Paul Smart